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This retrospective traces the hypothesis of ion channels from an early statement in a 1970 essay in this journal (Hille, B., 1970, Prog. Biophys. Mol. Biol. 21, 1–32) to its realization today in biophysical, molecular, biochemical, and structural terms. The Na(+) and K(+) channels of the action potential have been isolated, reconstituted, cloned, mutated, and expressed. They are conformationally flexible, multi-pass glycosylated membrane proteins. Refined atomic structures of several conformational states are known. The discoveries over this half century history illustrate the growth of a field from initial ideas to a mature discipline of biology, physiology, and biomedical science.

The aim of this study was to examine if the peripheral antinociception of α-bisabolol involves the participation of nitric oxide (NO) and cyclic guanosine monophosphate (cGMP) synthesis followed by K+ channel opening in the formalin test. Wistar rats were injected in the dorsal surface of the right hind paw with formalin (1%). Rats received a subcutaneous injection into the dorsal surface of the paw of vehicles or increasing doses of α-bisabolol (100–300 µg/paw). To determine whether the peripheral antinociception induced by α-bisabolol was mediated by either the opioid receptors or the NO-cGMP-K+ channels pathway, the effect of pretreatment (10 min before formalin injection) with the appropriate vehicles, naloxone, naltrexone, NG-nitro-l-arginine methyl ester (L-NAME), 1H-[1,2,4]-oxadiazolo[4,2-a]quinoxalin-1-one (ODQ), glibenclamide, glipizide, apamin, charybdotoxin, tetraethylammonium, or 4-aminopyridine on the antinociceptive effects induced by local peripheral α-bisabolol (300 µg/paw) were assessed. α-Bisabolol produced antinociception during both phases of the formalin test. α-Bisabolol antinociception was blocked by L-NAME, ODQ, and all the K+ channels blockers. The peripheral antinociceptive effect produced by α-bisabolol was not blocked by the opioid receptor inhibitors. α-Bisabolol was able to active the NO-cGMP-K+ channels pathway to produce its antinoceptive effect. The participation of opioid receptors in the peripheral local antinociception induced by α-bisabolol is excluded.

Potassium (K+) channels are highly conserved proteins found in all domains of life, that allow for selective movement of K+ ions across membranes. Despite their broad distribution, the physiological roles of individual members of this diverse channel family have only been thoroughly explored in eukaryotic systems, where they have critical functions in a variety of cellular processes. Recent studies have demonstrated that bacterial K+ channels have integral roles in electrical signaling, information propagation, and intercellular communication. We discuss how these novel findings impact our understanding of bacterial physiology and the need to continue to explore the native roles of ion channels in microbes.

© 2021 The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature., We have experimented with isolated cardiomyocytes of mollusks Helix. During the whole-cell patch-clamp recordings of K+ currents a considerable decrease in amplitude was observed upon repeated voltage steps at 0.96 Hz. For these experiments, ventricular cells were depolarized to identical + 20 mV from a holding potential of - 50 mV. The observed spontaneous inhibition of outward currents persisted in the presence of 4-aminopyridine, tetraethylammonium chloride or E-4031, the selective class III antiarrhythmic agent that blocks HERG channels. Similar tendency was retained when components of currents sensitive to either 4-AP or TEA were mathematically subtracted. Waveforms of currents sensitive to 1 and 10 micromolar concentration of E-4031 were distinct comprising prevailingly those activated during up to 200 ms pulses. The outward current activated by a voltage ramp at 60 mV x s-1 rate revealed an inward rectification around + 20 mV. This feature closely resembles those of the mammalian cardiac delayed rectifier IKr.

The 3',5'-cGMP pathway triggers cytoprotective responses and improves cardiomyocyte survival during myocardial ischaemia and reperfusion (I/R) injury. These beneficial effects were attributed to NO-sensitive GC induced cGMP production leading to activation of cGMP-dependent protein kinase I (cGKI). cGKI in turn phosphorylates many substrates, which eventually facilitate opening of mitochondrial ATP-sensitive potassium channels (mitoKATP ) and Ca2+ -activated potassium channels of the BK type (mitoBK). Accordingly, agents activating mitoKATP or mitoBK provide protection against I/R-induced damages. Here, we provide an up-to-date summary of the infarct-limiting actions exhibited by the GC/cGMP axis and discuss how mitoKATP and mitoBK, which are present at the inner mitochondrial membrane, confer mito- and cytoprotective effects on cardiomyocytes exposed to I/R injury. In view of this, we believe that the functional connection between the cGMP cascade and mitoK+ channels should be exploited further as adjunct to reperfusion therapy in myocardial infarction.

Basolateral Kir4.1/Kir5.1 in the distal convoluted tubule plays an important role as a “K+ sensor” in the regulation of renal K+ excretion after high K+ intake. We found that neural precursor cell expressed developmentally downregulated 4-2 (Nedd4-2) a role in mediating the effect of K+ diet on Kir4.1/Kir5.1 and NaCl cotransporter because high K+ intake failed to inhibit basolateral Kir4.1/Kir5.1 and NaCl cotransporter in kidney tubule-specific Nedd4-2 knockout mice.

Voltage-gated Kv7 ( KCNQ family) K+ channels are expressed in many neuronal populations and play an important role in regulating membrane potential by generating a hyperpolarizing K+ current and decreasing cell excitability. However, the role of KV7 channels in the neural regulation of intestinal epithelial Cl− secretion is not known. Cl− secretion in mouse distal colon was measured as a function of short-circuit current (ISC), and pharmacological approaches were used to test the hypothesis that activation of KV7 channels in enteric neurons would inhibit epithelial Cl− secretion. Flupirtine, a nonselective KV7 activator, inhibited basal Cl− secretion in mouse distal colon and abolished or attenuated the effects of drugs that target various components of enteric neurotransmission, including tetrodotoxin (NaV channel blocker), veratridine (NaV channel activator), nicotine (nicotinic acetylcholine receptor agonist), and hexamethonium (nicotinic antagonist). In contrast, flupritine did not block the response to epithelium-targeted agents VIP (endogenous VPAC receptor ligand) or carbachol (nonselective cholinergic agonist). Flupirtine inhibited Cl− secretion in both full-thickness and seromuscular-stripped distal colon (containing the submucosal, but not myenteric plexus) but generated no response in epithelial T84 cell monolayers. KV7.2 and KV7.3 channel proteins were detected by immunofluorescence in whole mount preparations of the submucosa from mouse distal colon. ICA 110381 (KV7.2/7.3 specific activator) inhibited Cl− secretion comparably to flupirtine. We conclude that KV7 channel activators inhibit neurally driven Cl− secretion in the colonic epithelium and may therefore have therapeutic benefit in treating pathologies associated with hyperexcitable enteric nervous system, such as irritable bowel syndrome with diarrhea (IBS-D).

Neurovascular coupling ensures rapid and precise delivery of O2 and nutrients to active brain regions. Chronic stress is known to disturb neurovascular signaling with grave effects on brain integrity. We hypothesized that stress-induced neurovascular disturbances depend on stress susceptibility. Wistar male rats were exposed to 8 weeks of chronic mild stress. Stressed rats with anhedonia-like behavior and with preserved hedonic state were identified from voluntary sucrose consumption. In brain slices from nonstressed, anhedonic, and hedonic rats, neurons and astrocytes showed similar intracellular Ca2+ responses to neuronal excitation. Parenchymal arterioles in brain slices from nonstressed, anhedonic, and hedonic rats showed vasodilation in response to neuronal excitation. This vasodilation was dependent on inward rectifying K+ channel (Kir2) activation. In hedonic rats, this vasodilation was transient and followed by vasoconstriction insensitive to Kir2 channel inhibition with 100 µM BaCl2. Isolated arteries from hedonic rats showed increased contractility. Elevation of bath K+ relaxed isolated middle cerebral arteries in a concentration-dependent and Kir2-dependent manner. The vasorelaxation to 20-24 mM K+ was reduced in arteries from hedonic rats. The expression of voltage-gated K+ channels, Kv7.4, was reduced in the cerebral arteries from hedonic rats, whereas the expression of arterial inward-rectifying K+ channels, Kir2.1 was similar to that of nonstressed and anhedonic rats. We propose that preserved hedonic state is associated with increased arterial contractility caused by reduced hyperpolarizing contribution of Kv7.4 channels leading to biphasic cerebrovascular responses to neuronal excitation. These findings reveal a novel potential coping mechanism associated with altered neurovascular signaling.

In this perspective, we discuss the physiological roles of Na and K channels, emphasizing the importance of the K channel for cellular homeostasis in animal cells and of Na and K channels for cellular signaling. We consider the structural basis of Na and K channel gating in light of recent structural and electrophysiological findings.

Various types of channels vary their function by membrane tension changes upon cellular activities, and lipid bilayer methods allow elucidation of direct interaction between channels and the lipid bilayer. However, the dynamic responsiveness of the channel to the membrane tension remains elusive. Here, we established a time-lapse tension measurement system. A bilayer is formed by docking two monolayer-lined water bubbles, and tension is evaluated via measuring intrabubble pressure as low as

The aim of this study was to establish the mechanisms of action of a novel liposomal nitric oxide (NO) carrier on large-conductance Ca2+-activated channels (BKCa or Maxi-K) expressed in vascular sm...

Background: Diabetes Mellitus (DM) is a major interna-tional health problem characterized by an absolute or relative deficiency in the production or action of insulin, which results in hyperglycemia. Unfortunately, long term insulin adminis-tration in patients with DM results in insulin resistance. In this work, a novel therapeutic strategy of one of the ATP sensitive K channel opener KATP openers called Nicorandil was tried as an adjuvant agent in ameliorating CVD in exper-imentally-induced type I DM in rats. Aim of Study: The present study was designed to elucidate possible role of K channels in glucose homeostasis and regulation of the vascular reactivity in diabetic rats. Material and Methods: Fifty adult male albino rats were used in this investigation, divided into following groups control: Non-diabetic (C), diabetic (D), diabetic insulin treated (D + I), diabetic nicorandil treated (D + N) and diabetic insulin and nicorandil treated (D + I + N). Blood samples were collected for estimation of Fasting Blood Glucose (FBG) and (HbA1c), and vascular reactivity was examined using different vasoactive agents. Results: Type 1 DM resulted in substantial alterations in biochemical variables, as fasting blood glucose level, HbA1c, ABP and vascular reactivity. In our study there is significant decrease in fasting blood glucose level, (HbA1c) in both diabetic insulin (D + I) treated group and diabetic insulin and nicorandil (D + I + N) treated group in compared with the diabetic group, but with insignif-icant change between the two groups. There was significant improvement in vascular reactivity in diabetic insulin (D + I) treated group, diabetic nicorandil (D + N) treated group and diabetic insulin and nicorandil (D + I + N) treated group in compared with the diabetic (D) non treated group, but with insignificant change between insulin and nicorandil (D + I + N) treated group and non-diabetic (C) group. Conclusion: Nicorandil can be used as an adjuvant therapy in diabetic rats to improve vascular reactivity.

We investigated the effect of ziprasidone, a widely used treatment for schizophrenia, on voltage-dependent K+ (Kv) channels of coronary arterial smooth muscle cells using the patch-clamp technique. Ziprasidone dose-dependently inhibited Kv channels with an IC50 value of 0.39 ± 0.06 μM and a Hill coefficient of 0.62 ± 0.03. Although ziprasidone had no effect on the steady-state inactivation kinetics of the Kv channels, the steady-state activation curve shifted towards a more positive potential. These results suggest that ziprasidone inhibits Kv channels by targeting their voltage sensors. The recovery time constant of Kv channel inactivation was increased in the presence of ziprasidone. Furthermore, application of train steps (of 1 and 2 Hz) in the presence of ziprasidone led to a progressive increase in the blockade of Kv currents, suggesting that ziprasidone-induced inhibition of Kv channels is use (state)-dependent. Pretreatment with Kv1.5, Kv2.1, and Kv7 subtype inhibitors partially suppressed the ziprasidone-induced inhibition of Kv currents. These results suggest that ziprasidone inhibits vascular Kv channels through its effect on gating properties. The Kv channel-inhibiting action of ziprasidone is concentration- and use (state)-depedent.

Microvascular endothelial dysfunction, a precursor to atherosclerotic cardiovascular disease, increases with aging. Endothelium-derived hyperpolarizing factors (EDHFs), which act through K+channels, regulate blood flow and are important to vascular health. It is unclear how EDHFs change with healthy aging. To evaluate microvascular endothelial reliance on K+channel-mediated dilation as a function of age in healthy humans. Microvascular function was assessed using intradermal microdialysis in healthy younger (Y; n = 7; 3 M/4 W; 26 ± 1 yr) and older adults (O; n = 12; 5 M/7 W; 64 ± 2 yr) matched for V̇o2peak(Y: 39.0 ± 3.8, O: 37.6 ± 3.1 mL·kg−1·min−1). Participants underwent graded local infusions of: the K+channel activator Na2S (10−6to 10−1M), acetylcholine (ACh, 10−10to 10−1M), ACh + the K+channel inhibitor tetraethylammonium (TEA; 25 or 50 mM), and ACh + the nitric oxide synthase-inhibitor l-NAME (15 mM). Red blood cell flux was measured with laser-Doppler flowmetry and used to calculate cutaneous vascular conductance (CVC; flux/mean arterial pressure) as a percentage of each site-specific maximum (%CVCmax, 43°C+28 mM sodium nitroprusside). The %CVCmaxresponse to Na2S was higher in older adults (mean, O: 51.7 ± 3.9% vs. Y: 36.1 ± 5.3%; P = 0.03). %CVCmaxwas lower in the ACh+TEA vs. the ACh site starting at 10−5M (ACh: 34.0 ± 5.7% vs. ACh+TEA: 19.4 ± 4.5%; P = 0.002) in older and at 10−4M (ACh: 54.5 ± 9.4% vs. ACh+TEA: 31.2 ± 6.7%; P = 0.0002) in younger adults. %CVCmaxwas lower in the ACh+l-NAME vs. the ACh site in both groups starting at 10−4M ACh (Y: P < 0.001; O: P = 0.02). Healthy active older adults have enhanced K+channel-dependent endothelial vasodilatory mechanisms, suggesting increased responsiveness to EDHFs with age.

TOKs are outwardly rectifying K+ channels in fungi with two pore-loops and eight transmembrane spans. Here, we describe the TOKs from four pathogens that cause the majority of life-threatening fungal infections in humans. These TOKs pass large currents only in the outward direction like the canonical isolate from Saccharomyces cerevisiae (ScTOK), and distinct from other K+ channels. ScTOK, AfTOK1 (Aspergillus fumigatus) and H99TOK (Cryptococcus neoformans grubii) are K+-selective and pass current above the K+ reversal potential. CaTOK (Candida albicans) and CnTOK (Cryptococcus neoformans neoformans) pass both K+ and Na+ and conduct above a reversal potential reflecting the mixed permeability of their selectivity filter. Mutations in CaTOK and ScTOK at sites homologous to those that open the internal gates in classical K+ channels are shown to produce inward TOK currents. A favored model for outward rectification is proposed whereby the reversal potential determines ion occupancy, and thus conductivity, of the selectivity filter gate that is coupled to an imperfectly restrictive internal gate, permitting the filter to sample ion concentrations on both sides of the membrane.

Background In the previous study, we investigated the alleviation effect of grafting on potassium uptake in roots and tobacco growth inhibition under low potassium stress. However, the effect of grafting on the low potassium stress perception and coping mechanism of tobacco at the whole plant level is not clear now. In order to clearly understand the impact of grafting on potassium deficit responding mechanism in tobacco, a mutual grafting experiment has been conducted in two varieties of tobacco (‘Wufeng No.2’ and ‘Yunyan 87’) in different K supply level (5 mmol L− 1 and 0.5 mmol L− 1 K). Results The results show that compared with the self-rooted seedlings, grafting significantly increased the potassium content of the whole plant of Yunyan 87 (97.57 and 189.74% under normal potassium and low potassium conditions, respectively), and the increase in shoots was greater. The data of whole plant K content distribution and tobacco hypocotyls net K+ flux demonstrates that potassium stress makes plants more inclined to maintain K+ in the shoot rather than root. In addition, when K deficiency occurs, grafting could reduce the time required for downward net K+ flux in tobacco hypocotyl to decrease to stable levels. The results of net K+ flux in the roots indicated that K channel proteins and transporters play different roles in two rootstocks in terms of potassium tolerance. Transcription level analysis suggested that the increased circulating efficiency of K+ between the shoots and roots in tobacco constitutes one means to low potassium stress adaptation. Conclusions Grafting can activate more K+ channels in tobacco ‘Yunyan 87’, this means a more active K+ cycle, higher potassium content in shoot and faster response to low potassium stress signals in grafting tobacco. In addition, grafting can also change the K+ absorption mode of tobacco root from being dominated by HATS to being jointly responsible by HATS and LATS, greatly improving the ability of K+ transmembrane transportation on root surface under low potassium stress. These are undoubtedly the reasons why grafting tobacco performs better in coping with low potassium stress.

Inwardly rectifying K+(Kir) channels are expressed in multiple organs and cell types and play critical roles in cellular function. Most notably, Kirchannels are major determinants of the resting membrane potential and K+homeostasis. The renal outer medullary K+channel (Kir1.1) was the first renal Kirchannel identified and cloned in the kidney over two decades ago. Since then, several additional members, including classical and ATP-regulated Kirfamily classes, have been identified to be expressed in the kidney and to contribute to renal ion transport. Although the ATP-regulated Kirchannel class remains the most well known due to severe pathological phenotypes associated with their mutations, progress is being made in defining the properties, localization, and physiological functions of other renal Kirchannels, including those localized to the basolateral epithelium. This review is primarily focused on the current knowledge of the expression and localization of renal Kirchannels but will also briefly describe their proposed functions in the kidney.

In visceral smooth muscle cells (SMCs), the large-conductance Ca2+-activated K+ (BK) channel is one of the key elements underlying a negative feedback mechanism that is essential for the regulation of intracellular Ca2+ concentration. Although leucine-rich repeat-containing (LRRC) proteins have been identified as novel auxiliary γ-subunits of the BK channel (BKγ) in several cell types, its physiological roles in SMCs are unclear. The BKγ expression patterns in selected SM tissues were examined using real-time PCR analyses and Western blotting. The functional contribution of BKγ1 to BK channel activity was examined by whole cell patch-clamp in SMCs and heterologous expression systems. BKγ1 expression in mouse bronchial SMCs (mBSMCs) was higher than in other several SMC types. Coimmunoprecipitation and total internal reflection fluorescence imaging analyses revealed molecular interaction between BKα and BKγ1 in mBSMCs. Under voltage-clamp, steady-state activation of BK channel currents at pCa 8.0 in mBSMCs occurred in a voltage range comparable to that of reconstituted BKα/BKγ1 complex. However, this range was much more negative than in mouse aortic SMCs (mASMCs) or in HEK293 cells expressing BKα alone and β-subunit (BKβ1). Mallotoxin, a selective activator of BK channel that lacks BKγ1, dose-dependently activated BK currents in mASMCs but not in mBSMCs. The abundant expression of BKγ1 in mBSMCs extensively facilitates BK channel activity to keep the resting membrane potential at negative values and prevents contraction under physiological conditions.

A minor alteration in structure of a previously reported synthetic K+ channel via replacing the electron-withdrawing group with an electron-donating group leads to enhancement in activity by 160% and in selectivity by >50%. As a result, the new K+ channel 10F5, despite having a simple structure, exhibits a high K+/Na+ selectivity of 14.0. Agency for Science, Technology and Research (A*STAR) This work is funded by the Agency for Science, Technology and Research, Singapore (SERC A1883c0007 to T. L.).

Downregulated expression of K+ channels and decreased K+ currents in pulmonary artery smooth muscle cells (PASMC) have been implicated in the development of sustained pulmonary vasoconstriction and vascular remodeling in patients with idiopathic pulmonary arterial hypertension (IPAH). However, it is unclear exactly how K+ channels are downregulated in IPAH-PASMC. MicroRNAs (miRNAs) are small non-coding RNAs that are capable of posttranscriptionally regulating gene expression by binding to the 3′-untranslated regions of their targeted mRNAs. Here, we report that specific miRNAs are responsible for the decreased K+ channel expression and function in IPAH-PASMC. We identified 3 miRNAs (miR-29b, miR-138, and miR-222) that were highly expressed in IPAH-PASMC in comparison to normal PASMC (>2.5-fold difference). Selectively upregulated miRNAs are correlated with the decreased expression and attenuated activity of K+ channels. Overexpression of miR-29b, miR-138, or miR-222 in normal PASMC significantly decreased whole cell K+ currents and downregulated voltage-gated K+ channel 1.5 (KV1.5/KCNA5) in normal PASMC. Inhibition of miR-29b in IPAH-PASMC completely recovered K+ channel function and KV1.5 expression, while miR-138 and miR-222 had a partial or no effect. Luciferase assays further revealed that KV1.5 is a direct target of miR-29b. Additionally, overexpression of miR-29b in normal PASMC decreased large-conductance Ca2+-activated K+ (BKCa) channel currents and downregulated BKCa channel β1 subunit (BKCaβ1 or KCNMB1) expression, while inhibition of miR-29b in IPAH-PASMC increased BKCa channel activity and BKCaβ1 levels. These data indicate upregulated miR-29b contributes at least partially to the attenuated function and expression of KV and BKCa channels in PASMC from patients with IPAH.

Refereed/Peer-reviewed KCNT1 (K+ channel subfamily T member 1) is a sodium-activated potassium channel highly expressed in the nervous system which regulates neuronal excitability by contributing to the resting membrane potential and hyperpolarisation following a train of action potentials. Gain of function mutations in the KCNT1 gene are the cause of neurological disorders associated with different forms of epilepsy. To gain insights into the underlying pathobiology we investigated the functional effects of 9 recently published KCNT1 mutations, 4 previously studied KCNT1 mutations, and one previously unpublished KCNT1 variant of unknown significance. We analysed the properties of KCNT1 potassium currents and attempted to find a correlation between the changes in KCNT1 characteristics due to the mutations and severity of the neurological disorder they cause. KCNT1 mutations identified in patients with epilepsy were introduced into the full length human KCNT1 cDNA using quick-change site-directed mutagenesis protocol. Electrophysiological properties of different KCNT1 constructs were investigated using a heterologous expression system (HEK293T cells) and patch clamping. All mutations studied, except T314A, increased the amplitude of KCNT1 currents, and some mutations shifted the voltage dependence of KCNT1 open probability, increasing the proportion of channels open at the resting membrane potential. The T314A mutation did not affect KCNT1 current amplitude but abolished its voltage dependence. We observed a positive correlation between the severity of the neurological disorder and the KCNT1 channel open probability at resting membrane potential. This suggests that gain of function KCNT1 mutations cause epilepsy by increasing resting potassium conductance and suppressing the activity of inhibitory neurons. A reduction in action potential firing in inhibitory neurons due to excessively high resting potassium conductance leads to disinhibition of neural circuits, hyperexcitability and seizures.

The tremorgenic fungal alkaloid paxilline (PAX) is a commonly used specific inhibitor of the large-conductance, voltage- and Ca 2+ -dependent BK-type K + channel. PAX inhibits BK channels by selective interaction with closed states. BK inhibition by PAX is best characterized by the idea that PAX gains access to the channel through the central cavity of the BK channel, and that only a single PAX molecule can interact with the BK channel at a time. The notion that PAX reaches its binding site via the central cavity and involves only a single PAX molecule would be consistent with binding on the axis of the permeation pathway, similar to classical open channel block and inconsistent with the observation that PAX selectively inhibits closed channels. To explore the potential sites of interaction of PAX with the BK channel, we undertook a computational analysis of the interaction of PAX with the BK channel pore gate domain guided by recently available liganded (open) and metal-free (closed) Aplysia BK channel structures. The analysis unambiguously identified a preferred position of PAX occupancy that accounts for all previously described features of PAX inhibition, including state dependence, G311 sensitivity, stoichiometry, and central cavity accessibility. This PAX-binding pose in closed BK channels is supported by additional functional results.

While plant voltage-dependent K+ channels embody many of the characteristics common among animal and bacterial channels, their gating continues to challenge mechanistic understanding., Potassium (K+) channels serve a wide range of functions in plants from mineral nutrition and osmotic balance to turgor generation for cell expansion and guard cell aperture control. Plant K+ channels are members of the superfamily of voltage-dependent K+ channels, or Kv channels, that include the Shaker channels first identified in fruit flies (Drosophila melanogaster). Kv channels have been studied in depth over the past half century and are the best-known of the voltage-dependent channels in plants. Like the Kv channels of animals, the plant Kv channels are regulated over timescales of milliseconds by conformational mechanisms that are commonly referred to as gating. Many aspects of gating are now well established, but these channels still hold some secrets, especially when it comes to the control of gating. How this control is achieved is especially important, as it holds substantial prospects for solutions to plant breeding with improved growth and water use efficiencies. Resolution of the structure for the KAT1 K+ channel, the first channel from plants to be crystallized, shows that many previous assumptions about how the channels function need now to be revisited. Here, I strip the plant Kv channels bare to understand how they work, how they are gated by voltage and, in some cases, by K+ itself, and how the gating of these channels can be regulated by the binding with other protein partners. Each of these features of plant Kv channels has important implications for plant physiology.

The fast transient outward potassium current (Ito,f) plays a key role in phase 1 repolarization of the human cardiac action potential (AP) and its reduction in heart failure (HF) contributes to the loss of contractility. Therefore, restoring Ito,f might be beneficial for treating HF. The coding sequence of a P2A peptide was cloned, in frame, between Kv4.3 and KChIP2.1 genes and ribosomal skipping was confirmed by Western blotting. Typical Ito,f properties with slowed inactivation and accelerated recovery from inactivation due to the association of KChIP2.1 with Kv4.3 was seen in transfected HEK293 cells. Both bicistronic components trafficked to the plasmamembrane and in adenovirus transduced rabbit cardiomyocytes both t-tubular and sarcolemmal construct labelling appeared. The resulting current was similar to Ito,f seen in human ventricular cardiomyocytes and was 50% blocked at ~0.8 mmol/l 4-aminopyridine and increased ~30% by 5 μmol/l NS5806 (an Ito,f agonist). Variation in the density of the expressed Ito,f, in rabbit cardiomyocytes recapitulated typical species-dependent variations in AP morphology. Simultaneous voltage recording and intracellular Ca2+ imaging showed that modification of phase 1 to a non-failing human phenotype improved the rate of rise and magnitude of the Ca2+ transient. Ito,f expression also reduced AP triangulation but did not affect ICa,L and INa magnitudes. This raises the possibility for a new gene-based therapeutic approach to HF based on selective phase 1 modification. ispartof: JOURNAL OF MOLECULAR AND CELLULAR CARDIOLOGY vol:164 pages:29-41 ispartof: location:England status: published

Calcium- and sodium- activated potassium channels are members of the 6TM family of K channels which comprises the voltage-gated KV subfamilies, including the KCNQ subfamily, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 6 or 7TM) and the Ca2+- and Na+-activated SK subfamily (nomenclature as agreed by the NC-IUPHAR Subcommittee on Calcium- and sodium-activated potassium channels [125]). As for the 2TM family, the pore-forming a subunits form tetramers and heteromeric channels may be formed within subfamilies (e.g. KV1.1 with KV1.2; KCNQ2 with KCNQ3).

The 2TM domain family of K channels are also known as the inward-rectifier K channel family. This family includes the strong inward-rectifier K channels (Kir2.x) that are constitutively active, the G-protein-activated inward-rectifier K channels (Kir3.x) and the ATP-sensitive K channels (Kir6.x, which combine with sulphonylurea receptors (SUR1-3)). The pore-forming α subunits form tetramers, and heteromeric channels may be formed within subfamilies (e.g. Kir3.2 with Kir3.3).

The 4TM family of K channels mediate many of the background potassium currents observed in native cells. They are open across the physiological voltage-range and are regulated by a wide array of neurotransmitters and biochemical mediators. The pore-forming α-subunit contains two pore loop (P) domains and two subunits assemble to form one ion conduction pathway lined by four P domains. It is important to note that single channels do not have two pores but that each subunit has two P domains in its primary sequence; hence the name two-pore domain, or K2P channels (and not two-pore channels). Some of the K2P subunits can form heterodimers across subfamilies (e.g. K2P3.1 with K2P9.1). The nomenclature of 4TM K channels in the literature is still a mixture of IUPHAR and common names. The suggested division into subfamilies, described in the More detailed introduction, is based on similarities in both structural and functional properties within subfamilies and this explains the "common abbreviation" nomenclature in the tables below.

The 6TM family of K channels comprises the voltage-gated KV subfamilies, the EAG subfamily (which includes hERG channels), the Ca2+-activated Slo subfamily (actually with 7TM, termed BK) and the Ca2+-activated SK subfamily. These channels possess a pore-forming α subunit that comprise tetramers of identical subunits (homomeric) or of different subunits (heteromeric). Heteromeric channels can only be formed within subfamilies (e.g. Kv1.1 with Kv1.2; Kv7.2 with Kv7.3). The pharmacology largely reflects the subunit composition of the functional channel.

TRAAK is a mechanosensitive two-pore domain K(+) (K2P) channel localized to nodes of Ranvier in myelinated neurons. TRAAK deletion in mice results in mechanical and thermal allodynia and gain-of-function mutations cause the human neurodevelopmental disorder FHEIG. TRAAK displays basal and stimulus-gated activities typical of K2Ps, but the mechanistic and structural differences between these modes are unknown. Here, we demonstrate that basal and mechanically-gated openings are distinguished by their conductance, kinetics, and structure. Basal openings are low conductance, short duration, and due to a conductive channel conformation with the interior cavity exposed to the surrounding membrane. Mechanically-gated openings are high conductance, long duration, and due to a channel conformation in which the interior cavity is sealed to the surrounding membrane. Our results explain how dual modes of activity are produced by a single ion channel and provide a basis for the development of state-selective pharmacology with the potential to treat disease.