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Introduction The principal voltage-gated Na+ channel, NaV1.5 governs heart excitability and conduction. NaV1.5 dysregulation is responsible for ventricular arrhythmias and subsequent sudden cardiac death (SCD) in post-infarct hearts. The transcription factor Meis1 performs a significant role in determining differentiation fate and regenerative capability of cardiomyocytes. However, the functions of Meis1 in ischemic arrhythmias following myocardial infarction (MI) are still largely undefined. Objectives Here we set out to study whether Meis1 could act as a key regulator to mediate cardiac Na+ channels and its underlying mechanisms. Methods Heart-specific Meis1 overexpression was established by AAV9 virus injection in C57BL/6 mice. The QRS duration, the incidence of ventricular arrhythmias and cardiac conduction velocity were evaluated by ECG, programmed electrical stimulation and optical mapping techniques respectively. The conventional patch clamp technique was performed to explore the INa characteristics of isolated mouse ventricular myocytes. In vitro, Meis1 was also overexpressed in hypoxic-treated neonatal cardiomyocytes. The analysis of immunoblotting and immunofluorescence were used to detect the changes in the expression of NaV1.5 in each group. Results We found that forced expression of Meis1 rescued the prolongation of QRS complex, produced anti-arrhythmic activity and improved epicardial conduction velocity in infarcted mouse hearts. In terms of mechanisms, the cardiac electrophysiological function of mice can be ameliorated by the recovery of Meis1, which is characterized by the restoration of INa current density and NaV1.5 expression level of cardiomyocytes in the marginal zone of myocardial infarction. Furthermore, the vitro studies showed that Meis1 was also able to rescue hypoxia-induced decreased expression and dysfunction of NaV1.5 in ventricular myocytes. We further revealed that E3 ubiquitin ligase CDC20 led to the ubiquitination and degradation of Meis1, which blocked the transcriptional regulation of SCN5A by Meis1 and ultimately led to the electrophysiological remodeling in ischemic-hypoxic cardiomyocytes. Conclusion CDC20 mediated ubiquitination of Meis1 to govern the transcription of SCN5A and cardiac electrical conductance in mouse cardiomyocytes. This finding uncovers a new mechanism of NaV1.5 dysregulation in infarcted heart, and provides new therapeutic strategies for malignant arrhythmias and sudden cardiac death following MI.

Background and aim Hydrocotyle bonariensis Comm ex Lamm (Araliaceae) is one of these plants sufficiently exploited in traditional African medicine for its hypotensive effect. However, the pharmacological effects of those plants on cardiac functions are not well known. The potassium currents IKs and IKr, responsible for the repolarization of cardiac cell action potential, strongly influence the human cardiac rhythm. Therefore, modulators of these currents have a beneficial or undesirable medical importance in relation to cardiac arrhythmias. In order to optimize the therapeutic use of this medicinal plant, we studied the effects of hydro-ethanolic leaf extract of Hydrocotyle bonariensis on both potassium currents. Experimental procedure The patch clamp experiments for IK currents recording were performed on the HEK 293 (Human Embryonic Kidney 293) cell line, stably transfected with either KCNQ1 and KCNE1 genes encoding the channel responsible for the "IKs" current (HEK293 IKs), or with hERG (human ether-a-go-go related gene) gene encoding "IKr" current (HEK293 IKr). Results and conclusion This study revealed that the hydro-ethanolic leaf extract of H. bonariensis significantly inhibits the slow potassium component (IKs) without altering the fast potassium component (IKr). The extract at 0.5 mg/ml decreases IKs conductance by 24 ± 4.1% (n = 6) without modifying its activation threshold suggesting a direct blockade of the slow potassium channel. This selective action of the extract on the IKs current reflects a class III anti-arrhythmic effect.

IntroductionLow voltage-activated T-type calcium channels (T-type ICa), CaV3.1, CaV3.2, and CaV3.3 are opened by small depolarizations from the resting membrane potential in many cells and have been associated with neurological disorders including absence epilepsy and pain. Δ9-tetrahydrocannabinol (THC) is the principal psychoactive compound in Cannabis and also directly modulates T-type ICa, however, there is no information about functional activity of most phytocannabinoids on T-type calcium channels, including Δ9-tetrahydrocannabinol acid (THCA), the natural non-psychoactive precursor of THC. The aim of this work was to characterize THCA effects on T-type calcium channels.Materials and MethodsWe used HEK293 Flp-In-TREx cells stably expressing CaV3.1, 3.2 or 3.3. Whole-cell patch clamp recordings were made to investigate cannabinoid modulation of ICa.ResultsTHCA and THC inhibited the peak current amplitude CaV3.1 with a pEC50s of 6.0 ± 0.7 and 5.6 ± 0.4, respectively. 1μM THCA or THC produced a significant negative shift in half activation and inactivation of CaV3.1 and both drugs prolonged CaV3.1 deactivation kinetics. THCA (10 μM) inhibited CaV3.2 by 53% ± 4 and both THCA and THC produced a substantial negative shift in the voltage for half inactivation and modest negative shift in half activation of CaV3.2. THC prolonged the deactivation time of CaV3.2 while THCA did not. THCA inhibited the peak current of CaV3.3 by 43% ± 2 (10μM) but did not notably affect CaV3.3 channel activation or inactivation, however, THC caused significant hyperpolarizing shift in CaV3.3 steady state inactivation.DiscussionTHCA modulated T-type ICa currents in vitro, with significant modulation of kinetics and voltage dependence at low μM concentrations. This study suggests that THCA may have potential for therapeutic use in pain and epilepsy via T-type channel modulation without the unwanted psychoactive effects associated with THC.

Layer 3 (L3) pyramidal neurons in aged rhesus monkey lateral prefrontal cortex (LPFC) exhibit significantly elevated excitability in vitro and reduced spine density compared to neurons in young subjects. The time-course of these alterations, and whether they can be ameliorated in middle age by the powerful anti-oxidant curcumin is unknown. We compared the properties of L3 pyramidal neurons from the LPFC of behaviorally characterized rhesus monkeys over the adult lifespan using whole-cell patch clamp recordings and neuronal reconstructions. Working memory (WM) impairment, neuronal hyperexcitability, and spine loss began in middle age. There was no significant relationship between neuronal properties and WM performance. Middle-aged subjects given curcumin exhibited better WM performance and less neuronal excitability compared to control subjects. These findings suggest that the appropriate time frame for intervention for age-related cognitive changes is early middle age, and points to the efficacy of curcumin in delaying WM decline. Because there was no relationship between excitability and behavior, the effects of curcumin on these measures appear to be independent.

Inflammation or trauma occurring on one side of the body can cause pathological pain on the contralateral noninjured side in a phenomenon called mirror-image pain (MIP). Although some potential mechanisms involved in MIP have been reported, including those involving the immune system and glial cells as well as neural mechanisms, the molecular mechanisms are not well understood. In this study, we aimed to understand the molecular mechanisms in MIP using quantitative proteomics and whole-cell patch clamp recordings. Behavioral test results showed that complete Freund's adjuvant could induce MIP in the mice. The results of isobaric tags for relative and absolute quantification (iTRAQ) quantitative proteomics showed that 108 proteins were dysregulated, and these proteins may represent potential targets. Furthermore, bioinformatics analysis was applied to explore the potential molecular mechanisms during MIP after complete Freund's adjuvant (CFA) treatment. Parallel reaction monitoring (PRM) results showed that PKCδ and seven other dysregulated proteins were related to MIP after CFA treatment. Patch clamp recording results showed that CFA treatment could increase intrinsic excitability and spontaneous firing in spinal cord neurons during MIP. In summary, we found that CFA could induce MIP. The results of proteomic research on the spinal cord after CFA treatment could provide new insight into the molecular mechanisms of MIP. Moreover, the neuronal activity of spinal cord neurons was upregulated during MIP after CFA treatment. In summary, the results of the spinal cord proteomic profile provide a potential molecular mechanism for understanding MIP.

Human corneal epithelial cells (HCEC), which are found on the outermost layer of the human cornea, play a vital role in maintaining vision. Research over the years has shown that various transient receptor potential channels (TRPs) are expressed on the surface of many ocular cells including the HCEC. With their intracellular and extracellular domains, TRPs are capable of converting external stimuli into signal transduction pathways within the cell. These channels play a significant role in Ca2+ regulation and mediate numerous intracellular processes by controlling the flow of Ca2+ ions across the cell membrane. Interestingly, studies have shown that growth factors can influence Ca2+ regulation via interaction with certain TRPs. As epidermal growth factor (EGF) in particular has been shown to promote healing of damaged corneal epithelial tissue, a closer study of the effect of EGF on HCEC would be useful. This study aims to investigate the influence EGF on Ca2+ regulation in cultured HCEC and the involvement of TRPs in this process. Fluorescence Ca2+ imaging of SV-40 transfected HCEC yielded the following results: Application of 50 ng/ml EGF caused a significant increase in intracellular Ca2+ concentration. This increase was significantly suppressed in the presence of the TRP canonical (TRPC) channel antagonist SKF 96365 (10–20 μM). When a Ca2+-free measuring solution was used, no increase in intracellular Ca2+ concentration was observed upon application of 50 ng/ml EGF. Patchclamp measurement of whole-cell currents revealed an increase in inward and outward currents through the cell membrane upon application of 50 ng/ml EGF. This EGFinduced increase in currents was suppressed in the presence of 20 μM SKF 96365. Taken together, this study demonstrates the involvement of TRPC channels in EGFinduced Ca2+ increase in HCEC. The results also suggest that this effect is due to EGFR-associated activation of TRPC channels on the cell membrane rather than the depletion of intracellular Ca2+ stores., Humane Hornhautepithelzellen (HCEC), die sich auf der äußersten Schicht der menschlichen Hornhaut befinden, spielen eine wichtige Rolle bei der Aufrechterhaltung des normalen Sehvermögens. Die Forschung im Laufe der Jahre zeigte, dass unterschiedliche Transient-Receptor-Potential-Kanäle (TRPs) in Zellen der Augenoberfläche einschließlich der HCEC exprimiert sind. Mit ihrer intra- und extrazellulären Domäne können TRPs externe Stimuli in Signaltransduktionswege innerhalb der Zelle umwandeln. Diese Kanäle spielen eine wichtige Rolle bei Ca2+- Regulation und vermitteln zahlreiche intrazelluläre Prozesse, indem sie den Fluss von Ca2+-Ionen durch die Zellmembran steuern. Interessanterweise zeigten Studien, dass Wachstumsfaktoren die Ca2+-Regulation durch Wechselwirkung mit bestimmten TRPs beeinflussen können. Da insbesondere der epidermale Wachstumsfaktor (EGF) gezeigt hat, dass er die Heilung von geschädigtem Hornhautepithelgewebe fördert, wäre eine nähere Untersuchung der Wirkung von EGF auf HCEC nützlich. Ziel dieser Studie ist es, den Einfluss von EGF auf die Ca2+-Regulation in kultivierten HCEC und die Beteiligung von TRPs an diesem Prozess zu untersuchen. Die Fluoreszenz-Ca2+- Image-Messungen von SV-40-transfizierten HCEC ergaben folgende Ergebnisse: Die extrazelluläre Applikation von 50 ng/ml EGF führte zu einem signifikanten Anstieg der intrazellulären Ca2+-Konzentration. Dieser Anstieg wurde in Gegenwart des kanonischen TRP (TRPC)-Kanalantagonisten SKF 96365 (10–20 μM) deutlich unterdrückt. Bei Verwendung einer Ca2+-freien Messlösung löste 50 ng/ml EGF keinen Anstieg der intrazellulären Ca2+-Konzentration aus. Patch-Clamp Messungen von Ganzzellströmen ergaben einen Anstieg der Ein- und Ausströme durch die Zellmembran nach Zugabe von 50 ng/ml EGF. Dieser EGF-induzierte Anstieg der Ströme wurde in Gegenwart von 20 μM SKF 96365 unterdrückt. Insgesamt deutet diese Studie eine Beteiligung von TRPC Kanäle am EGF-induzierten Ca2+-Anstieg in HCEC an. Die Ergebnisse weisen auch darauf hin, dass dieser Effekt eher auf ein EGFRassoziierte Aktivierung von TRPC Kanäle auf der Zellmembran zurückzuführen ist, als auf die Entleerung von intrazellulären Ca2+-Speichern.

La Trobe University Faculty of Science, Technology and Engineering Murray Darling Freshwater Research CentreMDFRC item.The ability to measure directly individual protoplast ion fluxes is a valuable addition to patch clamp and other techniques when using protoplasts to study membrane transporters. Before interpreting observations on protoplasts in terms of behaviour of intact cells and tissues, some methodological questions should be addressed. These include effects of space and time variations of transporter activities over the membrane, the osmotic dependence of specific ion transporters and the effect of the regenerating cell wall. In this study net H+ and Ca2+ fluxes were measured from individual corn (Zea mays L.) coleoptile protoplasts using a noninvasive microelectrode technique for ion flux measurements. For Ca2+, the flux distribution was almost symmetrical, ranging +/- 30 nmol.m(-2).s(-1) around zero. For H+ it was skewed towards efflux ranging from -100 to + 10 nmol.m(-2).s(-1). The distribution of H+ fluxes through the protoplast surface was a complex mosaic which changed with time, sometimes showing oscillations. These flux variations with time and position around the surface, apparently driven by endogenous mechanisms, may be relevant to protoplast pH homeostasis. When the new cell wall was partially regenerated on the next day, the correlation between H+ and Ca2+ fluxes increased. which is consistent with the weak-acid Donnan-Manning model of cell wall ion exchange.

Diverse physiological phenotypes in a neuronal population can broaden the range of computational capabilities within a brain region. The avian cochlear nucleus angularis (NA) contains a heterogeneous population of neurons whose variation in intrinsic properties results in electrophysiological phenotypes with a range of sensitivities to temporally modulated input. The low-threshold potassium conductance (GKLT) is a key feature of neurons involved in fine temporal structure coding for sound localization but a role for these channels in intensity or spectrotemporal coding has not been established. To determine whether GKLT affects the phenotypical variation and temporal properties of NA neurons, we applied dendrotoxin (DTX), a potent antagonist of Kv1-type potassium channels, to chick brain stem slices in vitro during whole-cell patch clamp recordings. We found a cell-type specific subset of NA neurons were sensitive to DTX: single-spiking NA neurons were most profoundly affected, as well as a subset of tonic firing neurons. Both tonic I (phasic onset bursting) and tonic II (delayed firing) neurons showed DTX sensitivity in their firing rate and phenotypical firing pattern. Tonic III neurons were unaffected. Spike time reliability and fluctuation sensitivity measured in DTX-sensitive NA neurons was also reduced with DTX. Finally, DTX reduced spike threshold adaptation in these neurons, suggesting that GKLT contributes to the temporal properties that allow coding of rapid changes in the inputs to NA neurons. These results suggest that variation in Kv1 channel expression may be a key factor in functional diversity in the avian cochlear nucleus.New and noteworthyThe dendrotoxin-sensitive voltage-gated potassium conductance typically associated with neuronal coincidence detection the timing pathway for sound localization is demonstrated to affect spiking patterns and temporal input sensitivity in the intensity pathway in the avian auditory brain stem. The Kv1-family channels appear to be present in a subset of cochlear nucleus angularis neurons, regulate spike threshold dynamics underlying high-pass membrane filtering, and contribute to intrinsic firing diversity.

Background and purpose Corpus cavernosum smooth muscle (CCSM) exhibits phasic contractions that are coordinated by ion channels. Mouse models are commonly used to study erectile dysfunction, but there are few published electrophysiological studies of mouse CCSM. We describe, for the first time, voltage-dependent sodium (NaV ) currents in mouse CCSM and investigate their function. Experimental approach Electrophysiological, pharmacological, and immunocytochemical studies on isolated CCSM cells. Tension measurements in whole tissue. Key results A fast, voltage-dependent sodium current was induced by depolarising steps. Steady-state activation and inactivation curves revealed a window current between -60 and -30 mV. Two populations of NaV currents, ('TTX-sensitive') and ('TTX-insensitive'), were distinguished. TTX-sensitive current showed 48% block with the NaV -subtype-specific blockers ICA-121431 (NaV 1.1-1.3), PF-05089771 (NaV 1.7), and 4,9-anhydro-TTX (NaV 1.6). TTX-insensitive current was insensitive to A803467, a NaV 1.8 blocker. Immunocytochemistry confirmed the expression of NaV 1.5 and NaV 1.4 in freshly dispersed CCSM cells. Veratridine, a NaV activator, reduced time-dependent inactivation of the current and increased the duration of evoked action potentials. Veratridine induced phasic contractions in CCSM strips. This effect was reversible with TTX and nifedipine but not by KB-R7943. Conclusion and implications We report, for the first time, a fast voltage-dependent sodium current in mouse CCSM. Stimulation of this current increases the contractility of corpus cavernosum in vitro, suggesting that it may contribute to the mechanisms of detumescence, and potentially serve as a clinically relevant target for pharmaceutical intervention in erectile dysfunction. Further work will be necessary to define its role.

Background and Purpose Voltage-gated sodium (Na-V) channels are expressed de novo in carcinomas where their activity promotes invasiveness. Breast and colon cancer cells express the neonatal splice variant of Na(V)1.5 (nNa(V)1.5), which has several amino acid substitutions in the domain I voltage-sensor compared with its adult counterpart (aNa(V)1.5). This study aimed to determine whether nNa(V)1.5 channels could be distinguished pharmacologically from aNa(V)1.5 channels. Experimental Approach Cells expressing either nNa(V)1.5 or aNa(V)1.5 channels were exposed to low MW inhibitors, an antibody or natural toxins, and changes in electrophysiological parameters were measured. Stable expression in EBNA cells and transient expression in Xenopus laevis oocytes were used. Currents were recorded by whole-cell patch clamp and two-electrode voltage-clamp, respectively. Key Results Several clinically used blockers of Na-V channels (lidocaine, procaine, phenytoin, mexiletine, ranolazine, and riluzole) could not distinguish between nNa(V)1.5 or aNa(V)1.5 channels. However, two tarantula toxins (HaTx and ProTx-II) and a polyclonal antibody (NESOpAb) preferentially inhibited currents elicited by either nNa(V)1.5 or aNa(V)1.5 channels by binding to the spliced region of the channel. Furthermore, the amino acid residue at position 211 (aspartate in aNa(V)1.5/lysine in nNa(V)1.5), that is, the charge reversal in the spliced region of the channel, played a key role in the selectivity, especially in antibody binding. Conclusion and Implications We conclude that the cancer-related nNa(V)1.5 channel can be distinguished pharmacologically from its nearest neighbour, aNa(V)1.5 channels. Thus, it may be possible to design low MW compounds as antimetastatic drugs for non-toxic therapy of nNa(V)1.5-expressing carcinomas.

Gap junction beta 1 (GJB1) is the pathogenic gene of X-linked Charcot-Marie-Tooth type 1 (CMTX1), a rare hereditary sensorimotor neuropathy. However, different mutations of GJB1 result in heterogeneous clinical manifestations with only some mutations leading to central nervous system involvement. We previously reported two GJB1 missense mutations: one novel mutation (c.212T > G) found in a CMTX1 family that only manifested as peripheral neuropathy, and another previously reported mutation GJB1(c.311A > C) leading to involvement of the peripheral nerves and cerebral white matter. However, the mechanism by which GJB1 mutations lead to CMTX1 has not been fully characterized. Here, we generated Schwann cells and primary cultured oligodendrocytes with these two mutations, resulting in the Cx32I71S (GJB1 c.212T > G) and Cx32K104T (GJB1 c.311A > C) mutants, to analyze the pathogenic mechanism using cytology, molecular biology, and electrophysiological methods. Both mutants showed abnormal endoplasmic reticulum aggregation, especially the Cx32K104T mutant, leading to an increase in endoplasmic reticulum stress, resulting in apoptosis. Furthermore, whole-cell patch clamp experiments in oligodendrocytes revealed that the Cx32K104T mutant reduced the cell membrane potential and inwardly rectifying potassium currents, which may be a vital element for central involvement. Therefore, our results may provide a new perspective for understanding the pathogenesis of CMTX1.

αO-Conotoxin GeXIVA is a 28 amino acid peptide derived from the venom of the marine snail Conus generalis. The presence of four cysteine residues in the structure of GeXIVA allows it to have three different disulfide isomers, that is, the globular, ribbon or bead isomer. All three isomers are active at α9α10 nicotinic acetylcholine receptors, with the bead isomer, GeXIVA[1,2], being the most potent and exhibiting analgesic activity in animal models of neuropathic pain. The original report of GeXIVA activity failed to observe any effect of the isomers on high voltage-activated (HVA) calcium channel currents in rat dorsal root ganglion (DRG) neurons. In this study, we report, for the first time, the activity of globular GeXIVA[1,3] at G protein-coupled GABA receptors (GABAR) inhibiting HVA N-type calcium (Cav2.2) channels and reducing membrane excitability in mouse DRG neurons. The inhibition of HVA Ba currents and neuroexcitability by GeXIVA[1,3] was partially reversed by the selective GABAR antagonist CGP 55845. In transfected HEK293T cells co-expressing human GABAR1 and R2 subunits and Cav2.2 channels, both GeXIVA[1,3] and GeXIVA[1,4] inhibited depolarization-activated Ba currents mediated by Cav2.2 channels, whereas GeXIVA[1,2] had no effect. The effects of three cyclized GeXIVA[1,4] ribbon isomers were also tested, with cGeXIVA GAG being the most potent at human GABAR-coupled Cav2.2 channels. Interestingly, globular GeXIVA[1,3] also reversibly potentiated inwardly-rectifying K currents mediated by human GIRK1/2 channels co-expressed with GABAR in HEK293T cells. This study highlights GABAR as a potentially important receptor target for the activity of αO-conotoxin GeXIVA to mediate analgesia. (Figure presented.).

Naturally found chrysosplenol-C (49,5,6-trihydroxy-3,39,7-trimethoxyflavone) increases the contractility of cardiac myocytes independent of b-adrenergic signaling. We investigated the cellular mechanism for chrysosplenol-C-induced positive inotropy. Global and local Ca2+ signals, L-type Ca2+ current (ICa), and contraction were measured from adult rat ventricular myocytes using two-dimensional confocal Ca2+ imaging, the whole-cell patch clamp technique, and video-edge detection, respectively. Application of chrysosplenol-C reversibly increased Ca2+ transient magnitude with a maximal increase of ~55% within 2-3-min-exposures (EC50 =~21 mM). This chemical did not alter ICa and slightly increased diastolic Ca2+ level. The frequency and size of resting Ca2+ sparks were increased by chrysosplenol-C. Chrysosplenol-C significantly increased sarcoplasmic reticulum (SR) Ca2+ content but not fractional release. Pretreatment of protein kinase C (PKC) inhibitor, but not Ca2+/calmodulin-dependent protein kinase II (CaMKII) inhibitor, abolished the stimulatory effects of chrysosplenol-C on Ca2+ transients and Ca2+ sparks. Chrysosplenol-C-induced positive inotropy was removed by the inhibition of PKC, but not CaMKII or phospholipase C. Western blotting assessment revealed that PKC-δ protein level in the membrane fractions significantly increase within 2 min after chrysosplenol-C exposure with a delayed (5 min) increase in PKC-α levels in insoluble membrane. These results suggest that chrysosplenol-C enhances contractility via PKC (most likely PKC-δ)-dependent enhancement of SR Ca2+ releases in ventricular myocytes. Significance Statement We show that chrysosplenol-C, a natural flavone showing a positive inotropic effect, increases sarcoplasmic reticulum (SR) Ca2+ releases on depolarizations and Ca2+ sparks with an increase of SR Ca2+ loading, but not L-type Ca2+ current, in ventricular myocytes. Chrysosplenol-C-induced enhancement in contraction is eliminated by protein kinase C (PKC) inhibition, and it is associated with redistributions of PKC to the membrane. These indicate that chrysosplenol-C enhances contraction via PKC-dependent augmentations of SR Ca2+ release and Ca2+ loading during action potentials.

BACKGROUND AND PURPOSE: In the activated state of small-conductance Ca(2+)-activated potassium (K(Ca) 2) channels, calmodulin interacts with the HA/HB helices and the S4-S5 linker. CyPPA potentiates K(Ca) 2.2a and K(Ca) 2.3 channel activity but not the K(Ca) 2.1 and K(Ca) 3.1 subtypes. EXPERIMENTAL APPROACH: Site-directed mutagenesis, patch-clamp recordings and in silico modeling were utilized to explore the structural determinants for the subtype-selective modulation of K(Ca) 2 channels by CyPPA. KEY RESULTS: Mutating residues in the HA (V420) and HB (K467) helices of K(Ca) 2.2a channels to their equivalent residues in K(Ca) 3.1 channels diminished the potency of CyPPA. CyPPA elicited prominent responses on mutant K(Ca) 3.1 channels with an arginine residue in the HB helix substituted for its equivalent lysine residue in the K(Ca) 2.2a channels (R355K). K(Ca) 2.1 channels harboring a three-amino-acid insertion upstream of the cognate R438 residues in the HB helix showed no response to CyPPA, whereas the deletion mutant (K(Ca) 2.1_ΔA434/Q435/K436) became sensitive to CyPPA. In molecular dynamics simulations, CyPPA docked between calmodulin C-lobe and the HA/HB helices widens the cytoplasmic gate of K(Ca) 2.2a channels. CONCLUSION AND IMPLICATIONS: Selectivity of CyPPA among K(Ca) 2 and K(Ca) 3.1 channel subtypes relies on the HA/HB helices.

The hippocampus is vulnerable to deterioration in Alzheimer's disease (AD). It is, however, a heterogeneous structure, which may contribute to the differential volumetric changes along its septotemporal axis during AD progression. Here, we investigated amyloid plaque deposition along the dorsoventral axis in two strains of transgenic AD (ADTg) mouse models. We also used patch-clamp physiology in these mice to probe for functional consequences of AD pathogenesis in ventral hippocampus, which we found bears significantly higher plaque burden in the aged ADTg group compared to corresponding dorsal regions. Despite dorsoventral differences in amyloid load, ventral CA1 pyramidal neurons of aged ADTg mice exhibited subthreshold physiological changes similar to those previously reported in dorsal neurons, indicative of an HCN channelopathy, but lacked exacerbated suprathreshold accommodation. Additionally, HCN channel function could be rescued by pharmacological manipulation of the endoplasmic reticulum. These observations suggest that an AD-linked HCN channelopathy emerges in both dorsal and ventral CA1 pyramidal neurons, but that the former encounter an additional integrative obstacle in the form of reduced intrinsic excitability.

Modulation of voltage-gated potassium (Kv) channels by auxiliary subunits is central to the physiological function of channels in the brain and heart1,2. Native Kv4 tetrameric channels form macromolecular ternary complexes with two auxiliary β-subunits—intracellular Kv channel-interacting proteins (KChIPs) and transmembrane dipeptidyl peptidase-related proteins (DPPs)—to evoke rapidly activating and inactivating A-type currents, which prevent the backpropagation of action potentials1–5. However, the modulatory mechanisms of Kv4 channel complexes remain largely unknown. Here we report cryo-electron microscopy structures of the Kv4.2–DPP6S–KChIP1 dodecamer complex, the Kv4.2–KChIP1 and Kv4.2–DPP6S octamer complexes, and Kv4.2 alone. The structure of the Kv4.2–KChIP1 complex reveals that the intracellular N terminus of Kv4.2 interacts with its C terminus that extends from the S6 gating helix of the neighbouring Kv4.2 subunit. KChIP1 captures both the N and the C terminus of Kv4.2. In consequence, KChIP1 would prevent N-type inactivation and stabilize the S6 conformation to modulate gating of the S6 helices within the tetramer. By contrast, unlike the reported auxiliary subunits of voltage-gated channel complexes, DPP6S interacts with the S1 and S2 helices of the Kv4.2 voltage-sensing domain, which suggests that DPP6S stabilizes the conformation of the S1–S2 helices. DPP6S may therefore accelerate the voltage-dependent movement of the S4 helices. KChIP1 and DPP6S do not directly interact with each other in the Kv4.2–KChIP1–DPP6S ternary complex. Thus, our data suggest that two distinct modes of modulation contribute in an additive manner to evoke A-type currents from the native Kv4 macromolecular complex., Cryo-electron microscopy structures of the voltage-gated potassium channel Kv4.2 alone and in complex with auxiliary subunits (DPP6S and/or KChIP1) reveal the distinct mechanisms of these two different subunits in modulating channel activity.

Background & purpose P2X4 is a ligand-gated cation channel activated by extracellular ATP, involved in neuropathic pain, inflammation and arterial tone. Experimental approach Natural products were screened against human or mouse P2X4 activity using fura-2 loaded 1321N1 cells for measurement of intracellular Ca2+ responses; whole-cell currents were measured by patch clamp electrophysiological. Human primary macrophage chemokine release was used to assess effect of taspine on inflammatory cell function. An enzymatic assay was performed to assess the effect of taspine on recombinant PI3-kinase. Key results A natural product screen identified taspine as an inhibitor of human P2X4 activity. Taspine inhibits human and mouse P2X4-mediated Ca2+ influx in 1321N1 cells expressing receptors (IC50 1.6±0.4 μM and 1.6±0.3 μM, respectively), but lacked activity at human P2X2, P2X3, P2X2/3 and P2X7 receptors. Taspine inhibited the maximal response at human and mouse P2X4 but had no effect on ATP potency. Taspine has a slow onset rate (~15 mins for half-maximal inhibition), irreversible over 30 minutes of washout. Taspine inhibits P2X4-mediated Ca2+ signalling in mouse BV-2 microglia cells and human primary macrophage. Taspine inhibited P2X4-mediated CXCL5 secretion in human primary macrophage. Taspine reversed ivermectin-induced potentiation of P2X4 currents in 1321N1 stably expressing cells. The known PI3-kinase inhibitor LY294002 mimicked the properties of taspine on P2X4-mediated Ca2+ influx and whole-cell currents. Taspine directly inhibited the enzymatic activity of recombinant PI3-kinase in a competitive manner. Conclusions and implications Taspine is a novel natural product P2X4 inhibitor, mediating its effect through PI3-kinase inhibitor rather than receptor antagonism. Taspine can inhibit the pro-inflammatory signalling by P2X4 in human primary macrophage.

Membrane proteins, including ion channels, became the focus of structural proteomics midway through the 20th century. Methods for studying ion channels are diverse and include structural (X-ray crystallography, cryoelectron microscopy, currently X-ray free electron lasers) and functional (e.g., patch clamp) approaches. This review highlights the evolution of approaches to study of the structure of cardiac ion channels, provides an overview of new techniques of structural biology concerning ion channels, including the use of lipo- and nanodiscs, and discusses the contribution of electrophysiological studies and molecular dynamics to obtain a complete picture of the structure and functioning of cardiac ion channels. Electrophysiological studies have become a powerful tool for deciphering the mechanisms of ion conductivity and selectivity, gating and regulation, as well as testing molecules of pharmacological interest. Obtaining the atomic structure of ion channels became possible by the active development of X-ray crystallography and cryoelectron micro-scopy, and, recently, with the use of XFEL.

Voltage gated calcium currents (VGCCs) in sensory neurons underlie processes ranging from neurotransmitter release to gene expression and remain a therapeutic target for the treatment of pain. Yet virtually all we know about VGCCs has been obtained through the study of rodent sensory neurons and heterologously expressed channels. To address this, high voltage activated (HVA) Ca2+ currents in dissociated human and rat dorsal root ganglion (DRG) neurons were characterized with whole cell patch clamp techniques. The HVA currents from both species shared basic biophysical and pharmacological properties. However, HVA currents in human neurons differed from those in the rat in at least three potentially important ways: (1) Ca2+ current density was significantly smaller, (2) the proportion of nifedipine-sensitive currents was far greater, and (3) a subpopulation of human neurons displayed relatively large constitutive current inhibition. These results highlight the need to for the study of native proteins in their native environment prior to initiating costly clinical trials.

Intermediate conductance potassium (IKCa) channels are exquisitively Ca2+ sensitive, intracellular Ca2+ regulating channel activity by complexing with calmodulin (CaM), which is bound to the cytosolic carboxyl tail. Although CaM antagonists might be expected to decrease IKCa channel activity, the effect of W-7 in human T lymphocytes are conflicting. We therefore evaluated the effect of W-7 on basolateral IKCa channels in human colonic crypt cells. Intact crypts obtained from normal human colonic biopsies by Ca2+ chelation were used for patch clamp studies of basolateral IKCa channels in the cell-attached configuration. IKCa channel activity was studied when the bath Ca2+ concentration was changed from 1.2 mmol/L to 100 μmol/L and back to 1.2 mmol/L, as well as from 100 μmol/L to 1.2 mmol/L and back to 100 μmol/L, both in the absence and presence of 25 μmol/L W-7. Decreasing bath Ca2+ from 1.2 mmol/L to 100 μmol/L decreased IKCa channel activity reversibly in the absence of W-7, whereas there was a uniformly high level of channel activity at both bath Ca2+ concentrations in the presence of W-7. In separate experiments, increasing bath Ca2+ from 100 μmol/L to 1.2 mmol/L increased IKCa channel activity reversibly in the absence of W-7, whereas there was again a uniformly high level of channel activity at both bath Ca2+ concentrations in the presence of W-7. We, therefore, propose that W-7 has a specific stimulatory effect on basolateral IKCa channel activity, despite its ability to inhibit Ca2+/CaM-mediated, IKCa channel-dependent Cl− secretion in human colonic epithelial cells. Graphic Abstract

Calcium signaling for host cell death In response to microbial pathogens, some plants kill off their own cells to limit further spread of infection. The Toll/Interleukin-1 receptor/Resistance class of nucleotide-binding leucine-rich repeat receptors (known as TNLs) function in plants as immune receptors. These TNLs work together with a dedicated set of helper proteins. Jacob et al. reveal the structure of one of these helpers known as NRG1 (N REQUIREMENT GENE 1). The structure resembles a known animal cation channel. The authors demonstrate that helper NLRs directly control calcium ion influx to initiate host cell death, providing a mechanism for TNL outputs. Science , abg7917, this issue p. 420

The organic anion balance is critical for metabolic, bioenergetic, and electrochemical processes in plant cells, controlling the quality and quantity of yield and plant stress resistance. Nevertheless, the redistribution and membrane transport of these substances in plant tissues have not been investigated in detail. The mechanism of passive anion efflux from a plant cell through the ion channels has not been established so far. Here, using the patch-clamp technique, we have characterized the ion channel-mediated conductances of ascorbate, malate, gluconate, citrate, fumarate, and pronionate in the root cells of Arabidopsis thaliana, Triticum aestivum, and Helianthus annuus. These conductances showed high permeability to ascorbate, malate, and citrate, as well as low permeability to fumarate, propionate, and gluconate. Anion channel conductances of root cells showed rapid activation kinetics and low potential dependence. They were also inhibited by 9-anthracenecarboxylic acid, suggesting that they belong to the ALMT family of anion channels found only in higher plants. Aequorin chemilu minometry was used to test the effect of organic anions on the Ca2+ signaling in root cells. Among four organic anions tested, only ascorbate induced a significant increase in the cytosolic Ca2+ activity at physiological levels (1 and 10 mM). This effect may underlie the previously unknown functions of exogenous ascorbate related to short- and long-distance signaling in higher plants.

Sodium salicylate is an anti-inflammatory medication with a side-effect of tinnitus. Here, we used mouse cochlear cultures to explore the effects of salicylate treatment on cochlear inner hair cells (IHCs). We found that IHCs showed significant damage after exposure to a high concentration of salicylate. Whole-cell patch clamp recordings showed that 1–5 mmol/L salicylate did not affect the exocytosis of IHCs, indicating that IHCs are not involved in tinnitus generation by enhancing their neuronal input. Instead, salicylate induced a larger peak amplitude, a more negative half-activation voltage, and a steeper slope factor of Ca(2+) current. Using noise analysis of Ca(2+) tail currents and qRT-PCR, we further found that salicylate increased the number of Ca(2+) channels along with Ca(V)1.3 expression. All these changes could act synergistically to enhance the Ca(2+) influx into IHCs. Inhibition of intracellular Ca(2+) overload significantly attenuated IHC death after 10 mmol/L salicylate treatment. These results implicate a cellular mechanism for tinnitus generation in the peripheral auditory system.

Several research programmes have demonstrated how Transcranial Ultrasound Stimulation (TUS) can non-invasively and reversibly mechanically perturb neuronal functions. However, the mechanisms through which such reversible and a priori non-damaging behaviour can be observed remain largely unknown. While several TUS protocols have demonstrated motor and behavioural alterations in in vivo models, in vitro studies remain scarce. In particular, an experimental framework able to load mechanically an individual neuron in a controlled manner and simultaneously measure the generation and evolution of action potentials before, during and after such load, while allowing for direct microscopy, has not been successfully proposed. To this end, we herein present a multiphysics setup combining nanoindentation and patch clamp systems, assembled in an inverted microscope for simultaneous bright-field or fluorescence imaging. We evaluate the potential of the platform with a set of experiments in which single dorsal root ganglion-derived neuronal cell bodies are compressed while their spontaneous activity is recorded. We show that these transient quasi-static mechanical loads reversibly affect the amplitude and rate of change of the neuronal action potentials, which are smaller and slower upon indentation, while irreversibly altering other features. The ability to simultaneously image, mechanically and electrically manipulate and record single cells in a perturbed mechanical environment makes this system particularly suitable for studying the multiphysics of the brain at the cell level.

Introduction Fibroblast growth factor homologous factors (FHFs), among other fibroblast growth factors, are increasingly found to be important regulators of ion channel functions. Although FHFs have been link to several neuronal diseases and arrhythmia, its role in inflammatory pain still remains unclear. Objectives This study aimed to investigate the role and mechanism of FGF13 in inflammatory pain. Methods Fgf13 conditional knockout mice were generated and CFA-induced chronic inflammatory pain model was established to measure the pain threshold. Immunostaining, western blot and quantitative real-time reverse transcription PCR (qRT-PCR) were performed to detect the expression of FGF13 in CFA-induced inflammatory pain. Whole-cell patch clamp recording was used to record the action potential firing properties and sodium currents of DRG neurons. Results Conditional knockout of Fgf13 in dorsal root ganglion (DRG) neurons (Fgf13-/Y) led to attenuated pain responses induced by complete Freund's adjuvant (CFA). FGF13 was expressed predominantly in small-diameter DRG neurons. CFA treatment resulted in an increased expression of FGF13 proteins as well as an increased excitability in nociceptive DRG neurons which was inhibited when FGF13 was absent. The role of FGF13 in neuronal excitability of DRG was linked to its modulation of voltage-gated Na+ channels mediated by microtubules. Overexpression of FGF13, but not FGF13 mutant which lacks the ability to bind and stabilize microtubules, rescued the decreased neuronal excitability and Na+ current density in DRG neurons of Fgf13-/Y mice. Conclusion This study revealed that FGF13 could stabilize microtubules to modulate sodium channel function in DRG neurons and modulate inflammatory pain. This study provides a novel mechanism for FGF13 modulation of sodium channel function and suggests that FGF13 might be a novel target for inflammatory pain treatment.

Classical high-throughput screening (HTS) technologies for the analysis of ionic currents across biological membranes can be performed using fluorescence-based, radioactive, and mass spectrometry (MS)-based uptake assays. These assays provide rapid results for pharmacological HTS, but the underlying, indirect analytical character of these assays can be linked to high false-positive hit rates. Thus, orthogonal and secondary assays using more biological target-based technologies are indispensable for further compound validation and optimization. Direct assay technologies for transporter proteins are electrophysiology-based, but are also complex, time-consuming, and not well applicable for automated profiling purposes. In contrast to conventional patch clamp systems, solid supported membrane (SSM)-based electrophysiology is a sensitive, membrane-based method for transporter analysis, and current technical developments target the demand for automated, accelerated, and sensitive assays for transporter-directed compound screening. In this study, the suitability of the SSM-based technique for pharmacological compound identification and optimization was evaluated performing cell-free SSM-based measurements with the electrogenic amino acid transporter B0AT1 (SLC6A19). Electrophysiological characterization of leucine-induced currents demonstrated that the observed signals were specific to B0AT1. Moreover, B0AT1-dependent responses were successfully inhibited using an established in-house tool compound. Evaluation of current stability and data reproducibility verified the robustness and reliability of the applied assay. Active compounds from primary screens of large compound libraries were validated, and false-positive hits were identified. These results clearly demonstrate the suitability of the SSM-based technique as a direct electrophysiological method for rapid and automated identification of small molecules that can inhibit B0AT1 activity.

Lens gap junctions (GJs) formed by Cx46 and Cx50 are important to keep lens transparency. Functional studies on Cx46 and Cx50 GJs showed that the Vj-gating, single channel conductance (γj), gating polarity, and/or channel open stability could be modified by the charged residues in the amino terminal (NT) domain. The role of hydrophobic residues in the NT on GJ properties is not clear. Crystal and cryo-EM GJ structures have been resolved, but the NT domain structure has either not been resolved or has showed very different orientations depending on the component connexins and possibly other experimental conditions, making it difficult to understand the structural basis of the NT in Vj-gating and γj. Here, we generated missense variants in Cx46 and Cx50 NT domains and studied their properties by recombinant expression and dual whole-cell patch clamp experiments on connexin-deficient N2A cells. The NT variants (Cx46 L10I, N13E, A14V, Q15N, and Cx50 I10L, E13N, V14A, N15Q) were all able to form functional GJs with similar coupling%, except Cx46 N13E, which showed a significantly reduced coupling%. The GJs of Cx46 N13E, A14V and Cx50 E13N, N15Q showed a reduced coupling conductance. Vj-gating of all the variant GJs were similar to the corresponding wild-type GJs except Cx46 L10I. The γj of Cx46 N13E, A14V, Cx50 E13N, and N15Q GJs was reduced to 51%, 82%, 87%, and 74%, respectively, as compared to their wild-type γjs. Structural models of Cx46 L10I and A14V predicted steric clashes between these residues and the TM2 residues, which might be partially responsible for our observed changes in GJ properties. To verify the importance of hydrophobic interactions, we generated a variant, Cx50 S89T, which also shows a steric clash and failed to form a functional GJ. Our experimental results and structure models indicate that hydrophobic interactions between the NT and TM2 domain are important for their Vj-gating, γj, and channel open stability in these and possibly other GJs.

electrophysiology patch clamp neuronal excitability

Aripiprazole is an atypical antipsychotic drug, which is prescribed for many psychiatric diseases such as schizophrenia and mania in bipolar disorder. It primarily acts as an agonist of dopaminergic and other G-protein coupled receptors. So far, an interaction with ligand- or voltage-gated ion channels has been classified as weak. Meanwhile, we identified aripiprazole in a preliminary test as a potent blocker of voltage-gated sodium channels. Here, we present a detailed analysis about the interaction of aripiprazole with the dominant voltage-gated sodium channel of heart muscle (hNav1.5). Electrophysiological experiments were performed by means of the patch clamp technique at human heart muscle sodium channels (hNav1.5), heterologously expressed in human TsA cells. Aripiprazole inhibits the hNav1.5 channel in a state- but not use-dependent manner. The affinity for the resting state is weak with an extrapolated Kr of about 55 µM. By contrast, the interaction with the inactivated state is strong. The affinities for the fast and slow inactivated state are in the low micromolar range (0.5–1 µM). Kinetic studies indicate that block development for the inactivated state must be described with a fast (ms) and a slow (s) time constant. Even though the time constants differ by a factor of about 50, the resulting affinity constants were nearly identical (in the range of 0.5 µM). Besides this, aripirazole also interacts with the open state of the channel. Using an inactivation deficit mutant, an affinity of about 1 µM was estimated. In summary, aripiprazole inhibits voltage-gated sodium channels at low micromolar concentrations. This property might add to its possible anticancer and neuroprotective properties.

Gastrointestinal motility was disturbed in W/Wv, which were lacking of interstitial cells of Cajal (ICC). In this study, we have investigated the role of arecoline hydrobromide (AH) on smooth muscle motility in the jejunum of W/Wv and wild-type (WT) mice. The jejunum tension was recorded by an isometric force transducer. Intracellular recording was used to identify whether AH affects slow wave and resting membrane potential (RMP) in vitro. The whole-cell patch clamp technique was used to explore the effects of AH on voltage-dependent potassium channels for jejunum smooth muscle cells. AH enhanced W/Wv and WT jejunum contractility in a dose-dependent manner. Atropine and nicardipine completely blocked the excitatory effect of AH in both W/Wv and WT. TEA did not reduce the effect of AH in WT, but was sufficient to block the excitatory effect of AH in W/Wv. AH significantly depolarized the RMP of jejunum cells in W/Wv and WT. After pretreatment with TEA, the RMP of jejunum cells indicated depolarization in W/Wv and WT, but subsequently perfused AH had no additional effect on RMP. AH inhibited the voltage-dependent K+ currents of acutely isolated mouse jejunum smooth muscle cells. Our study demonstrate that AH enhances the contraction activity of jejunum smooth muscle, an effect which is mediated by voltage-dependent potassium channels that acts to enhance the excitability of jejunum smooth muscle cells in mice.

GABA type A receptors (GABAARs) belong to the pentameric ligand-gated ion channel (pLGIC) family and play a crucial role in mediating inhibition in the adult mammalian brain. Recently, a major progress in determining the static structure of GABAARs was achieved, although precise molecular scenarios underlying conformational transitions remain unclear. The ligand binding sites (LBSs) are located at the extracellular domain (ECD), very distant from the receptor gate at the channel pore. GABAAR gating is complex, comprising three major categories of transitions: openings/closings, preactivation, and desensitization. Interestingly, mutations at, e.g., the ligand binding site affect not only binding but often also more than one gating category, suggesting that structural determinants for distinct conformational transitions are shared. Gielen and co-workers (2015) proposed that the GABAAR desensitization gate is located at the second and third transmembrane segment. However, studies of our and others’ groups indicated that other parts of the GABAAR macromolecule might be involved in this process. In the present study, we asked how selected point mutations (β2G254V, α1G258V, α1L300V, and β2L296V) at the M2 and M3 transmembrane segments affect gating transitions of the α1β2γ2 GABAAR. Using high resolution macroscopic and single-channel recordings and analysis, we report that these substitutions, besides affecting desensitization, also profoundly altered openings/closings, having some minor effect on preactivation and agonist binding. Thus, the M2 and M3 segments primarily control late gating transitions of the receptor (desensitization, opening/closing), providing a further support for the concept of diffuse gating mechanisms for conformational transitions of GABAAR.

The cystic fibrosis transmembrane conductance regulator (CFTR) Cl− channel shows only weak selectivity between different small monovalent anions, however, little is known about its ability to discriminate between monovalent and divalent anions. The present study uses patch clamp recording to investigate the interaction between the small divalent anions S2O32− and SO42− and wild-type and pore-mutant forms of human CFTR. Binding of these anions to wild-type CFTR appears weak; at 10 mM, intracellular S2O32− and SO42− blocked

Voltage-gated sodium channels are currently recognized as one of the targets of analgesics. Magnolol (Mag), an active component isolated from Magnolia officinalis, has been reported to exhibit analgesic effects. The objective of this study was to investigate whether the analgesic effect of Mag was associated with blocking Na+ channels. Inflammatory pain was induced by the injection of carrageenan into the hind paw of mice. Mag was administered orally. Mechanical hyperanalgesia was evaluated by using von Frey filaments. Na+ currents and neuronal excitability in acutely isolated mouse dorsal root ganglion (DRG) neurons were recorded with the whole-cell patch clamp technique. Results showed that Mag (10 ~ 40 mg/kg) dose-dependently inhibited the paw edema and reduced mechanical pain in the inflammatory animal model. Injection of carrageenan significantly increased the amplitudes of TTX-sensitive and TTX-resistant Na+ currents. Compared with the carrageenan group, Mag inhibited the upregulation of two types of Na+ currents induced by carrageenan in a dose-dependent manner. Mag 40 mg/kg shifted the inactivation curves of two types of Na+ currents to hyperpolarization and returned to normal animal level without changing their activation curves. Mag 40 mg/kg significantly reduced the percentage of cells firing multiple spikes and inhibited the neuronal hyperexcitability induced by carrageenan. Our data suggest that the analgesic effect of Mag may be associated with a decreased neuronal excitability by blocking Na+ current.

Spontaneous burst firing is a hallmark attributed to the neuronal network activity. It is known to be accompanied by intracellular calcium [Са2+]i oscillations within the bursting neurons. Studying mechanisms underlying regulation of burst firing is highly relevant, since impairment in neuronal bursting accompanies different neurological disorders. In the present study, the contribution of NMDA and GABA(A) receptors to the shape formation of spontaneous burst -was studied in cultured hippocampal neurons. A combination of inhibitory analysis with simultaneous registration of neuronal bursting by whole-cell patch clamp and calcium imaging was used to assess spontaneous burst firing and [Са2+]i level. Using bicuculline and D-AP5 we showed that GABA(A) and NMDA receptors effectively modulate burst plateau phase and [Са2+]i transient spike which can further affect action potential (AP) amplitudes and firing frequency within a burst. Bicuculline significantly elevated the amplitude and reduced the duration of both burst plateau phase and [Са2+]i spike resulting in an increase of AP firing frequency and shortening of AP amplitudes within a burst. D-AP5 significantly decreases the amplitude of both plateau phase and [Са2+]i spike along with a burst duration that correlated with an increase in AP amplitudes and reduced firing frequency within a burst. The effect of bicuculline was occluded by co-addition of D-AP5 revealing modulatory role of GABA(A) receptors to the NMDA receptor-mediated formation of the burst. Our results provide new evidence on importance of NMDA and GABA(A) receptors in shaping burst firing and Ca2+transient spikes in cultured hippocampal neurons.

Protozoan parasites acquire essential ions, nutrients and other solutes from their insect and vertebrate hosts by transmembrane uptake. For intracellular stages, these solutes must cross additional membranous barriers. At each step, ion channels and transporters mediate not only this uptake, but also the removal of waste products. These transport proteins are best isolated and studied with patch-clamp, but these methods remain accessible to only a few parasitologists due to specialized instrumentation and the required training into both theory and practice. Here, we provide an overview of patch-clamp, describing the advantages and limitations of the technology and highlighting issues that may lead to incorrect conclusions. We aim to help non-experts understand and critically assess patch-clamp data in basic research studies.

Potassium ions have widespread roles in cellular homeostasis and activation as a consequence of their large outward concentration gradient across the surface membrane and ability to rapidly move through K+-selective ion channels. In platelets, the predominant K+ channels include the voltage-gated K+ channel Kv1.3, and the intermediate conductance Ca2+-activated K+ channel KCa3.1, also known as the Gardos channel. Inwardly rectifying potassium GIRK channels and KCa1.1 large conductance Ca2+-activated K+ channels have also been reported in the platelet, although they remain to be demonstrated using electrophysiological techniques. Whole-cell patch clamp and fluorescent indicator measurements in the platelet or their precursor cell reveal that Kv1.3 sets the resting membrane potential and KCa3.1 can further hyperpolarize the cell during activation, thereby controlling Ca2+ influx. Kv1.3-/- mice exhibit an increased platelet count, which may result from an increased splenic megakaryocyte development and longer platelet lifespan. This review discusses the evidence in the literature that Kv1.3, KCa3.1. GIRK and KCa1.1 channels contribute to a number of platelet functional responses, particularly collagen-evoked adhesion, procoagulant activity and GPCR function. Putative roles for other K+ channels and known accessory proteins which to date have only been detected in transcriptomic or proteomic studies, are also discussed.

Birds acquired endothermy and a four-chambered heart independently from mammals in the course of evolution. Though avian embryos are widely used in experiments, little is known about the adult avian heart. Recent studies have shown that, despite a large evolutionary distance, the set of repolarizing potassium currents in avian myocardium resembles that in mammalian heart as well as that in humans. This allows for proposing birds as a potential model in experimental cardiology. The present study for the first time describes inward rectifier currents in working myocardium of quail. Using patch clamp method, we recorded main background inward rectifier current IK1 was recorded in isolated atrial and ventricular cardiomyocytes of quail. Both inward and outward components of IK1 in ventricular cells were larger than those in atrial cells, while there were no differences in voltage dependence of inward rectification. Acetylcholine and carbachol induced activation of acetylcholine-dependent inward rectifier current IKACh in atrial but not in ventricular myocytes. IKACh in atrial myocytes was sensitive to tertiapin. Constitutively active IKACh has not been detected. In multicellular preparations of the quail right atrium, carbachol induced hyperpolarization and shortening of action potentials, while no such effects were observed in preparations of the right ventricle. Activation of IKACh upon application of carbachol was dose-dependent with EC50 = 4.922 × 10–7 М. The described distribution of inward rectifier currents in avian myocardium is similar to that in mammalian species, which are widely used as model objects in experimental cardiology.

Deep brain stimulation (DBS) of the subcallosal cingulate gyrus (SCG) is a promising therapy for treatment-resistant depression. Pre-clinical models have been widely used to investigate the neural mechanisms underlying its antidepressant benefit. The ventral division of the medial prefrontal cortex (vmPFC), particularly the infralimbic cortex (IL), is the homologous region in rat and DBS applied to vmPFC shows antidepressant-like effects in the forced swim test. Therefore we investigated the cellular mechanisms of simulated DBS (sDBS) in layer 5 IL neurons, using in vitro whole-cell patch clamp recordings. sDBS in IL layer 5 induced a prolonged after-depolarization (ADP) in both pyramidal and fast spiking neurons, which was dependent on current amplitude and pulse width. In contrast, sDBS applied in the forebrain white matter fibers, although delivered at a higher intensity, failed to induce any persistent depolarization in layer 5 IL pyramidal neurons. Cholinergic blockade (atropine, 2.0 µM) decreased both the ADP amplitude and duration in pyramidal neurons, but left those in fast spiking neurons unchanged. These data suggest that: (i) sDBS in IL gray and white matter produced different cellular effects on pyramidal neurons; (ii) sDBS-induced ADP in pyramidal, but not fast spiking neurons, was mediated by acetylcholine; and (iii) different neuromodulators may contribute to sDBS-induced ADP in IL. In summary, cholinergic mediated ADP in pyramidal neurons may contribute to the antidepressant effects of DBS in IL.

Suppression of the cardiac sodium channel NaV1.5 leads to fatal arrhythmias in ischemic heart disease (IHD). However, the transcriptional regulation of NaV1.5 in cardiac ischemia is still unclear. Our studies are aimed to investigate the expression of enhancer of zeste homolog 2 (EZH2) in IHD and regulation of cardiac NaV1.5 expression by EZH2. Human heart tissue was obtained from IHD and non-failing heart (NFH) patients; mouse heart tissue was obtained from the peri-infarct zone of hearts with myocardial infarction (MI) and hearts with a sham procedure. Protein and mRNA expression were measured by immunoblotting, immunostaining, and qRT-PCR. Protein-DNA binding and promoter activity were analyzed by ChIP-qPCR and luciferase assays, respectively. Na+ channel activity was assessed by whole-cell patch clamp recordings. EZH2 and H3K27me3 were increased while NaV1.5 expression was reduced in IHD hearts and in mouse MI hearts compared to the controls. Reduced NaV1.5 and increased EZH2 mRNA levels were observed in mouse MI hearts. A selective EZH2 inhibitor, GSK126 decreased H3K27me3 and elevated NaV1.5 in HL-1 cells. Silencing of EZH2 expression decreased H3K27me3 and increased NaV1.5 in these cells. EZH2 and H3K27me3 were enriched in the promoter regions of Scn5a and were decreased by treatment with EZH2 siRNA. GSK126 inhibited the enrichment of H3K27me3 in the Scn5a promoter and enhanced Scn5a transcriptional activity. GSK126 significantly increased Na+ channel activity. Taken together, EZH2 is increased in ischemic hearts and epigenetically suppresses Scn5a transcription by H3K27me3, leading to decreased NaV1.5 expression and Na+ channel activity underlying the pathogenesis of arrhythmias.

Cone snails are predatory gastropod mollusks that are distributed in all tropical marine environments and contain small peptides (conotoxins) in their venom to capture prey. However, the biochemical and molecular aspects of conotoxins remain poorly understood. In this article, a novel α4/7-conotoxin, Lv1d, was obtained from the venom duct cDNA library of the worm-hunting Conus lividus collected from the South China Sea. The cDNA of Lv1c encodes a 65 residue conopeptide precursor, which consists of a 21 residue signal peptide, a 27 residue Pro region, and 17 residues of mature peptide. The mature peptide Lv1d was chemically synthesized according to the sequence GCCSDPPCRHKHQDLCG. It was found that 10 μM Lv1d can completely inhibit frog sciatic nerve-gastrocnemius muscle contractility within 60 min. Moreover, 100 μg/kg Lv1d showed good analgesic effects in mouse hot plate model and formalin test. Patch clamp experiments showed that 5 μM Lv1d can inhibit the cholinergic microexcitatory postsynaptic currents (mEPSCs) requency and amplitude of projection neurons in Drosophila. In conclusion, the synthesis of Lv1d and its biological and physiological data might contribute to the development of this peptide as a novel potential drug for therapeutic applications. This finding also expands the knowledge of the targeting mechanism of the α4/7-subfamily conotoxins.

In this paper, the multifractal properties of the ion current time series in the fast-activating vacuolar (FV) channels of Beta vulgaris L. taproot cells were investigated. These channels are permeable for only monovalent cations and mediate K+ at very low concentrations of cytosolic Ca2+ and large voltages of either polarity. Using the patch clamp technique, the currents of the FV channels in red beet taproot vacuoles were recorded and analysed by using the multifractal detrended fluctuation analysis (MFDFA) method. The activity of the FV channels depended on the external potential and was sensitive to the auxin. It was also shown that the singularity spectrum of the ion current in the FV channels is non-singular, and the multifractal parameters, i.e., the generalised Hurst exponent and the singularity spectrum, were modified in the presence of IAA. Taking into account the obtained results, it can be suggested that the multifractal properties of fast-activating vacuolar (FV) K+ channels, indicating the existence of long-term memory, should be taken into account in the molecular mechanism of the auxin-induced growth of plant cells.

Ca2+-activated chloride channel TMEM16A has been found to be overexpressed in many cancers including head and neck squamous cell carcinoma (HNSCC). Nevertheless, the role of TMEM16A in oral squamous cell carcinoma (OSCC) remains unclear. Although simvastatin is known to produce anti-tumor effect, the mechanisms by which simvastatin inhibits cancer remain unclear. In this study, we explored the role of TMEM16A expression in human OSCC tissues using both TCGA dataset and immunohistochemistry. CCK-8 assay was applied to evaluate cell proliferation. Patch clamp technique was applied to record TMEM16A Cl− currents. We found that high TMEM16A expression is related with large tumor size, lymph node metastasis, and poor clinical outcome in patients with OSCC. In addition, TMEM16A overexpression could promote cell proliferation, and inhibition of TMEM16A channel activities could suppress cell proliferation in OSCC cells. Furthermore, simvastatin could suppress TMEM16A channel activities, and inhibited cell proliferation in OSCC cells via TMEM16A. Our findings identify a novel anti-tumor mechanism of simvastatin by targeting TMEM16A. Simvastatin may represent an innovative strategy for treating OSCC with high TMEM16A expression.

The magnocellular neurosecretory cells (MNCs) of the hypothalamus play a vital role in osmoregulation, but the mechanisms underlying MNC osmosensitivity are not fully understood. We showed previously that high osmolality activates phospholipase C (PLC) in rat MNCs in a Ca2+-dependent manner and that PLC activation is necessary for full osmotic activation of an N-terminal variant of the TRPV1 (ΔN-TRPV1) channel. We therefore hypothesized that the Ca2+-dependent δ1 isoform of PLC contributes to ΔN-TRPV1 activation and tested whether MNC function is defective in a transgenic PLCδ1 KO mouse. Water deprivation for 24 h caused greater increases in serum osmolality and losses in body weight in PLCδ1 KO mice than it did in control mice. Action potentials and ΔN-TRPV1 currents were measured in acutely isolated mouse MNCs using whole-cell patch clamp before and after exposure to hypertonic solutions. This treatment elicited a significant activation of ΔN-TRPV1 currents and an increase in firing rate in MNCs isolated from control mice, but not from PLCδ1 KO mice. Submembranous filamentous actin was measured in isolated MNCs before and after treatment with angiotensin II and hypertonic solution. Both treatments caused an increase in filamentous actin fluorescence in MNCs isolated from control mice, but both responses were significantly attenuated in MNCs from PLCδ1 KO mice. Our data demonstrate that the PLCδ1 isoform plays a key role in the activation of ΔN-TRPV1 channels and in osmosensory transduction in MNCs. This study advances our understanding of the molecular mechanisms underlying mammalian osmoregulation.SIGNIFICANCE STATEMENTMagnocellular neurosecretory cells (MNCs) of the hypothalamus play a central role in osmoregulation. We have identified a key role for the PLCδ1 isoform in the activation of ΔN-TRPV1 channels and osmosensory transduction in MNCs. The data indicate that the PLCδ1 isoform is activated by the Ca2+influx occurring during MNC action potentials and exerts a positive feedback on ΔN-TRPV1 channels to enhance MNC excitability. This study provides evidence that PLCδ1 is a key molecule underlying osmosensory transduction, the regulation of VP release, and osmoregulation.

We investigated how oxidative stress (OS) alters Ca2+ handling in ventricular myocytes in early metabolic syndrome (MetS) in sucrose-fed rats. The effects of N-acetyl cysteine (NAC) or dl-Dithiothreitol (DTT) on systolic Ca2+ transients (SCaTs), diastolic Ca2+ sparks (CaS) and Ca2+ waves (CaW), recorded by confocal techniques, and L-type Ca2+ current (ICa), assessed by whole-cell patch clamp, were evaluated in MetS and Control cells. MetS myocytes exhibited decreased SCaTs and CaS frequency but unaffected CaW propagation. In Control cells, NAC/DTT reduced RyR2/SERCA2a activity blunting SCaTs, CaS frequency and CaW propagation, suggesting that basal ROS optimised Ca2+ signalling by maintaining RyR2/SERCA2a function and that these proteins facilitate CaW propagation. Conversely, NAC/DTT in MetS recovered RyR2/SERCA2a function, improving SCaTs and CaS frequency, but unexpectedly decreasing CaW propagation. We hypothesised that OS decreases RyR2/SERCA2a activity at early MetS, and while decreased SERCA2a favours CaW propagation, diminished RyR2 restrains it.

Ivermectin (IVM) belongs to the class of macrocyclic lactones, which is used as an antiparasitic agent. At present, the researchers focus on possibility to use IVM in treatment of certain forms of cancer and viral diseases such as COVID-19. The mechanisms of IVM action are not clear. It is assumed that IVM affects chloride channels and increases cytoplasmic concentration of chloride. This study examines the effect of IVM on chloride currents induced by glycine (IGly). Experiments were carried out on isolated pyramidal neurons of the rat hippocampus with whole-cell patch clamp. A short-term (600 msec) application of IVM in a concentration of 10 μM induced a slow inward current, which persisted after washing the neurons. The low concentrations (0.1-1000 nM) of IVM did not induce any novel current, but it rapidly and reversibly reduced the peak amplitude and accelerated desensitization of IGly in a dose-dependent manner. The threshold concentrations of IVM sufficient to reduce peak amplitude of IGly and to accelerate desensitization of IGly were 100 nM and 0.1 nM, respectively. The study revealed a high sensitivity of neuronal glycine receptors to IVM.

In this study, we have revisited the existing and suggested new approaches to the use of patch-clamp methodology for measuring the activity of single ion channels and membrane potential of human platelets in the cell-attached configuration. We recorded single-channel events of platelets in the cell-attached configuration after activation with potent agonists: thrombin and ionomycin. The feasibility of platelet membrane potential measurement in cell-attached mode was investigated both experimentally and with the help of simple electrical circuits, revealing that the single-channel events can alter the recorded potential by invoking oscillations. Here, the simple approach to obtain inside-out configuration was described and calcium-dependent single-channel ion currents were recorded. Taken together, this study introduces new approaches for further investigations of the role of ion channels and membrane potential in platelet physiological and pathophysiological response.

Innate-like CD5+ B1a cells localized in serous cavities are activated by innate stimuli, such as lipopolysaccharide (LPS), leading to T cell-independent antibody responses. Although ion channels play crucial roles in the homeostasis and activation of immune cells, the electrophysiological properties of B1a cells have not been investigated to date. Previously, in the mouse B cell lymphoma cells, we found that the voltage-independent two-pore-domain potassium (K2P) channels generate a negative membrane potential and drive Ca2+ influx. Here, we newly compared the expression and activities of K2P channels in mouse splenic follicular B (FoB), marginal zone B (MZB), and peritoneal B1a cells. Next-generation sequencing analysis showed higher levels of transcripts for TREK-2 and TWIK-2 in B1a cells than those in FoB or MZB cells. Electrophysiological analysis, using patch clamp technique, revealed higher activity of TREK-2 with the characteristic large unitary conductance (~ 250 pS) in B1a than that in FoB or MZB cells. TREK-2 activity was further increased by LPS treatment (>2 h), which was more prominent in B1a than that in MZB or FoB cells. The cytosolic Ca2+ concentration of B cells was decreased by high-K+-induced depolarization (ΔRKCl (%)), suggesting the basal Ca2+ influx to be driven by negative membrane potential. The LPS treatment significantly increased the ΔRKCl (%) in B1a, though not in FoB and MZB cells. Our study was the first to compare the K2P channels in mouse primary B cell subsets, elucidating the functional upregulation of TREK-2 and augmentation of Ca2+ influx by the stimulation of Toll-like receptor 4 in B1a cells.

The GABAA receptor is a member of the Cys-loop family and plays a crucial role in the adult mammalian brain inhibition. Although the static structure of this receptor is emerging, the molecular mechanisms underlying its conformational transitions remain elusive. It is known that in the Cys-loop receptors, the interface between extracellular and transmembrane domains plays a key role in transmitting the "activation wave" down to the channel gate in the pore. It has been previously reported that histidine 55 (H55), located centrally at the interfacial β1-β2 loop of the α1 subunit, is important in the receptor activation, but it is unknown which specific gating steps it is affecting. In the present study, we addressed this issue by taking advantage of the state-of-the-art macroscopic and single-channel recordings together with extensive modeling. Considering that H55 is known to affect the local electrostatic landscape and because it is neighbored by two negatively charged aspartates, a well conserved feature in the α subunits, we considered substitution with negative (E) and positive (K) residues. We found that these mutations markedly affected the receptor gating, altering primarily preactivation and desensitization transitions. Importantly, opposite effects were observed for these two mutations strongly suggesting involvement of electrostatic interactions. Single-channel recordings suggested also a minor effect on opening/closing transitions which did not depend on the electric charge of the substituting amino acid. Altogether, we demonstrate that H55 mutations affect primarily preactivation and desensitization most likely by influencing local electrostatic interactions at the receptor interface.

Objectives: Cryopreserved chondrocytes find numerous applications in reconstructive surgery, tissue engineering, and cell-based therapy. Cryopreserved chondrocytes may behave differently due to a change in cell biology. To assess phenotype maintenance, the electrophysiological profile of the cells can be studied. In this study, a comparison between freshly isolated and cryopreserved chondrocytes was made by recording ionic currents using patch clamp. Materials and Methods: Caprine articular chondrocytes were harvested and cryopreserved for 7–15 days and divided into two groups. Percentage cell viability was assessed, following which both fresh and cryopreserved cells were subjected to analysis in whole cell configuration using depolarizing voltage steps. Results: Outwardly, rectifying currents were recorded in both groups. Comparison of current densities at all potentials above the threshold, revealed no significant difference between fresh and cryopreserved chondrocytes. Conclusion: As electrophysiological properties of cryopreserved chondrocytes appear to be maintained, they may be readily utilized in place of fresh cells.

Bestrophins are a family of calcium-activated chloride channels (CaCCs) with relevance to human physiology and a myriad of eye diseases termed “bestrophinopathies”. Since the identification of bestrophins as CaCCs nearly two decades ago, extensive studies from electrophysiological and structural biology perspectives have sought to define their key channel features including calcium sensing, gating, inactivation, and anion selectivity. The initial X-ray crystallography studies on the prokaryotic homolog of Best1, Klebsiella pneumoniae (KpBest), and the Best1 homolog from Gallus gallus (chicken Best1, cBest1), laid the foundational groundwork for establishing the architecture of Best1. Recent progress utilizing single-particle cryogenic electron microscopy has further elucidated the molecular mechanism of gating in cBest1 and, separately, the structure of Best2 from Bos taurus (bovine Best2, bBest2). Meanwhile, whole-cell patch clamp, planar lipid bilayer, and other electrophysiologic analyses using these models as well as the human Best1 (hBest1) have provided ample evidence describing the functional properties of the bestrophin channels. This review seeks to consolidate these structural and functional results to paint a broad picture of the underlying mechanisms comprising the bestrophin family’s structure-function relationship.