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Scientific reports 11, 6934 (2021). doi:10.1038/s41598-021-85656-x, Published by Macmillan Publishers Limited, part of Springer Nature, [London]

Channels 15(1), 208-228 (2021). doi:10.1080/19336950.2020.1870087, Published by Taylor & Francis, Abingdon, Oxon

Data in Brief 31, 105844 (2020). doi:10.1016/j.dib.2020.105844, Published by Elsevier, Amsterdam [u.a.]

The journal of biological chemistry : JBC 296, 100227 (2020). doi:10.1074/jbc.RA120.014288, Published by American Society for Biochemistry and Molecular Biology, Bethesda, Md.

Voltage-gated sodium channels are responsible not only for the fast upstroke of the action potential, but they also modify cellular excitability via persistent and resurgent currents. Insecticides act via permanently opening sodium channels to immobilize the animals. Cellular recordings performed decades ago revealed distinctly hooked tail currents induced by these compounds. Here, we applied the classical type-II pyrethroid deltamethrin on human cardiac Nav1.5 and observed resurgent-like currents at very negative potentials in the absence of any pore-blocker, which resemble those hooked tail currents. We show that deltamethrin dramatically slows both fast inactivation and deactivation of Nav1.5 and thereby induces large persistent currents. Using the sea anemone toxin ATx-II as a tool to prevent all inactivation-related processes, resurgent-like currents were eliminated while persistent currents were preserved. Our experiments suggest that, in deltamethrin-modified channels, recovery from inactivation occurs faster than delayed deactivation, opening a brief window for sodium influx and leading to hooked, resurgent-like currents, in the absence of an open channel blocker. Thus, we now explain with pharmacological methods the biophysical gating changes underlying the deltamethrin induced hooked tail currents. SUMMARY: The pyrethroid deltamethrin induces hooked resurgent-like tail currents in human cardiac voltage-gated Nav1.5 channels. Using deltamethrin and ATx-II, we identify additional conducting channel states caused by a faster recovery from inactivation compared to the deltamethrin-induced delayed deactivation.

British journal of pharmacology : BJP 177(19), 4481-4496 (2020). doi:10.1111/bph.15196, Published by Wiley, Malden, MA

Mutations in voltage-gated sodium channels are associated with altered pain perception in humans. Most of these mutations studied to date present with a direct and intuitive link between the altered electrophysiological function of the channel and the phenotype of the patient. In this study, we characterize a variant of Nav1.8, D1639N, which has been previously identified in a patient suffering from the chronic pain syndrome "small fiber neuropathy". Using a heterologous expression system and patch-clamp analysis, we show that Nav1.8/D1639N reduces current density without altering biophysical gating properties of Nav1.8. Therefore, the D1639N variant causes a loss-of-function of the Nav1.8 sodium channel in a patient suffering from chronic pain. Using immunocytochemistry and biochemical approaches, we show that Nav1.8/D1639N impairs trafficking of the channel to the cell membrane. Neither co-expression of β1 or β3 subunit, nor overnight incubation at 27 °C rescued current density of the D1639N variant. On the other hand, overnight incubation with lidocaine fully restored current density of Nav1.8/D1639N most likely by overcoming the trafficking defect, whereas phenytoin failed to do so. Since lidocaine rescues the loss-of-function of Nav1.8/D1639N, it may offer a future therapeutic option for the patient carrying this variant. These results demonstrate that the D1639N variant, identified in a patient suffering from chronic pain, causes loss-of-function of the channel due to impaired cell surface trafficking and that this trafficking defect can be rescued by lidocaine.

BACKGROUND AND PURPOSE: Oxycodone is a potent semi‐synthetic opioid that is commonly used for the treatment of severe acute and chronic pain. However, treatment with oxycodone can lead to cardiac electrical changes, such as long QT syndrome, potentially inducing sudden cardiac arrest. Here, we investigate whether the cardiac side effects of oxycodone can be explained by modulation of the cardiac Na(v)1.5 sodium channel. EXPERIMENTAL APPROACH: Heterologously expressed human Na(v)1.5, Na(v)1.7 (HEK293 cells) or Na(v)1.8 channels (mouse N1E‐115 cells) were used for whole‐cell patch‐clamp electrophysiology. A variety of voltage‐clamp protocols were used to test the effect of oxycodone on different channel gating modalities. Human stem cell‐derived cardiomyocytes were used to measure the effect of oxycodone on cardiomyocyte beating. KEY RESULTS: Oxycodone inhibited Na(v)1.5 channels, concentration and use‐dependently, with an IC(50) of 483 μM. In addition, oxycodone slows recovery of Na(v)1.5 channels from fast inactivation and increases slow inactivation. At high concentrations, these effects lead to a reduced beat rate in cardiomyocytes and to arrhythmia. In contrast, no such effects could be observed on Na(v)1.7 or Na(v)1.8 channels. CONCLUSIONS AND IMPLICATIONS: Oxycodone leads to an accumulation of Na(v)1.5 channels in inactivated states, with a slow time course. Although the concentrations needed to elicit cardiac arrhythmias in vitro are relatively high, some patients under long‐term treatment with oxycodone as well as drug abusers and addicts might suffer from severe cardiac side effects induced by the slowly developing effects of oxycodone on Na(v)1.5 channels.

Key points The voltage-gated sodium channel Nav1.7 is a key player in neuronal excitability and pain signalling. In addition to voltage sensing, the channel is also modulated by mechanical stress. Using whole-cell patch-clamp experiments, we discovered that the sodium channel subunit β1 is able to prevent the impact of mechanical stress on Nav1.7. An intramolecular disulfide bond of β1 was identified to be essential for stabilisation of inactivation, but not activation, against mechanical stress using molecular dynamics simulations, homology modelling and site-directed mutagenesis. Our results highlight the role of segment 6 of domain IV in fast inactivation. We present a candidate mechanism for sodium channel stabilisation against mechanical stress, ensuring reliable channel functionality in living systems. Abstract Voltage-gated sodium channels are key players in neuronal excitability and pain signalling. Precise gating of these channels is crucial as even small functional alterations can lead to pathological phenotypes such as pain or heart failure. Mechanical stress has been shown to affect sodium channel activation and inactivation. This suggests that stabilising components are necessary to ensure precise channel gating in living organisms. Here, we show that mechanical shear stress affects voltage dependence of activation and fast inactivation of the Nav1.7 channel. Co-expression of the β1 subunit, however, protects both gating modes of Nav1.7 against mechanical shear stress. Using molecular dynamics simulation, homology modelling and site-directed mutagenesis, we identify an intramolecular disulfide bond of β1 (Cys21-Cys43) which is partially involved in this process: the β1-C43A mutant prevents mechanical modulation of voltage dependence of activation, but not of fast inactivation. Our data emphasise the unique role of segment 6 of domain IV for sodium channel fast inactivation and confirm previous reports that the intracellular process of fast inactivation can be modified by interfering with the extracellular end of segment 6 of domain IV. Thus, our data suggest that physiological gating of Nav1.7 may be protected against mechanical stress in a living organism by assembly with the β1 subunit.

The voltage-gated sodium channel Nav1.7 is essential for an adequate perception of painful stimuli. Its mutations cause various pain syndromes in human patients. The hNav1.7/A1632E mutation induces symptoms of erythromelalgia and paroxysmal extreme pain disorder (PEPD), and its main gating change is a strongly enhanced persistent current.Using molecular simulations, we demonstrate that the disease causing persistent current of hNav1.7/A1632E is due to impaired binding of the IFM motif, thus affecting proper function of the recently proposed allosteric fast inactivation mechanism. By using native polyacrylamide gel electrophoresis (PAGE) gels, we show that hNav1.7 dimerizes. The disease-linked persistent current depends on the channel’s functional dimerization status: Using difopein, a 14-3-3 inhibitor known to uncouple dimerization of hNav1.5, we detect a significant decrease in hNav1.7/A1632E induced persistent currents.Our work identifies that functional uncoupling of hNav1.7/A1632E dimers rescues the pain-causing molecular phenotype by interferes with an allosteric fast inactivation mechanism, which we link for the first time to channel dimerization. Our work supports the concept of sodium channel dimerization and reveals its relevance to human pain syndromes.

The homotrimeric P2X3 receptor, one of the seven members of the ATP-gated P2X receptor family, plays a crucial role in sensory neurotransmission. P2X3 receptor antagonists have been identified as promising drugs to treat chronic cough and are suggested to offer pain relief in chronic pain such as neuropathic pain. Here, we analysed whether compounds affect P2X3 receptor activity by high-throughput screening of the Spectrum Collection of 2000 approved drugs, natural products and bioactive substances. We identified aurintricarboxylic acid (ATA) as a nanomolar-potency antagonist of P2X3 receptor-mediated responses. Two-electrode voltage clamp electrophysiology-based concentration–response analysis and selectivity profiling revealed that ATA strongly inhibits the rP2X1 and rP2X3 receptors (with IC50 values of 8.6 nM and 72.9 nM, respectively) and more weakly inhibits P2X2/3, P2X2, P2X4 or P2X7 receptors (IC50 values of 0.76 μM, 22 μM, 763 μM or 118 μM, respectively). Patch-clamp analysis of mouse DRG neurons revealed that ATA inhibited native P2X3 and P2X2/3 receptors to a similar extent than rat P2X3 and P2X2/3 receptors expressed in Xenopus oocytes. In a radioligand binding assay, up to 30 μM ATA did not compete with [3H]-ATP for rP2X3 receptor binding, indicating a non-competitive mechanism of action. Molecular docking studies, site-directed mutagenesis and concentration–response analysis revealed that ATA binds to the negative allosteric site of the hP2X3 receptor. In summary, ATA as a drug-like pharmacological tool compound is a nanomolar-potency, allosteric antagonist with selectivity towards αβ-methylene-ATP-sensitive P2X1 and P2X3 receptors.

Supplemental Digital Content is Available in the Text. Human sodium channel NaV1.7 in induced pluripotent stem cell–derived sensory neurons sets the action potential threshold but does not support subthreshold depolarizations., The chronic pain syndrome inherited erythromelalgia (IEM) is attributed to mutations in the voltage-gated sodium channel (NaV) 1.7. Still, recent studies targeting NaV1.7 in clinical trials have provided conflicting results. Here, we differentiated induced pluripotent stem cells from IEM patients with the NaV1.7/I848T mutation into sensory nociceptors. Action potentials in these IEM nociceptors displayed a decreased firing threshold, an enhanced upstroke, and afterhyperpolarization, all of which may explain the increased pain experienced by patients. Subsequently, we investigated the voltage dependence of the tetrodotoxin-sensitive NaV activation in these human sensory neurons using a specific prepulse voltage protocol. The IEM mutation induced a hyperpolarizing shift of NaV activation, which leads to activation of NaV1.7 at more negative potentials. Our results indicate that NaV1.7 is not active during subthreshold depolarizations, but that its activity defines the action potential threshold and contributes significantly to the action potential upstroke. Thus, our model system with induced pluripotent stem cell–derived sensory neurons provides a new rationale for NaV1.7 function and promises to be valuable as a translational tool to profile and develop more efficacious clinical analgesics.

Background Small fiber neuropathy (SFN) is a severe and disabling chronic pain syndrome with no causal and limited symptomatic treatment options. Mechanistically based individual treatment is not available. We report an in-vitro predicted individualized treatment success in one therapy-refractory Caucasian patient suffering from SFN for over ten years. Methods Intrinsic excitability of human induced pluripotent stem cell (iPSC) derived nociceptors from this patient and respective controls were recorded on multi-electrode (MEA) arrays, in the presence and absence of lacosamide. The patient's pain ratings were assessed by a visual analogue scale (10: worst pain, 0: no pain) and treatment effect was objectified by microneurography recordings of the patient's single nerve C-fibers. Findings We identified patient-specific changes in iPSC-derived nociceptor excitability in MEA recordings, which were reverted by the FDA-approved compound lacosamide in vitro. Using this drug for individualized treatment of this patient, the patient's pain ratings decreased from 7.5 to 1.5. Consistent with the pain relief reported by the patient, microneurography recordings of the patient's single nerve fibers mirrored a reduced spontaneous nociceptor (C-fiber) activity in the patient during lacosamide treatment. Microneurography recordings yielded an objective measurement of altered peripheral nociceptor activity following treatment. Interpretation Thus, we are here presenting one example of successful patient specific precision medicine using iPSC technology and individualized therapeutic treatment based on patient-derived sensory neurons., Graphical abstract Unlabelled Image

The transient receptor potential ankyrin 1 (TRPA1) ion channel is expressed in pain-sensing neurons and other tissues and has become a major target in the development of novel pharmaceuticals. A remarkable feature of the channel is its long list of activators, many of which we are exposed to in daily life. Many of these agonists induce pain and inflammation, making TRPA1 a major target for anti-inflammatory and analgesic therapies. Studies in human patients and in experimental animals have confirmed an important role for TRPA1 in a number of pain conditions. Over the recent years, much progress has been made in elucidating the molecular structure of TRPA1 and in discovering binding sites and modulatory sites of the channel. Because the list of published mutations and important molecular sites is steadily growing and because it has become difficult to see the forest for the trees, this review aims at summarizing the current knowledge about TRPA1, with a special focus on the molecular structure and the known binding or gating sites of the channel.

Key points The transient receptor potential ankyrin 1 (TRPA1) ion channel is expressed in nociceptive neurons and its activation causes ongoing pain and inflammation; TRPA1 is thought to play an important role in inflammation in the airways. TRPA1 is sensitised by repeated stimulation with chemical agonists in a calcium-free environment and this sensitisation is very long lasting following agonist removal. We show that agonist-induced sensitisation is independent of the agonist's binding site and is also independent of ion channel trafficking or of other typical signalling pathways. We find that sensitisation is intrinsic to the TRPA1 protein and is accompanied by a slowly developing shift in the voltage dependence of TRPA1 towards more negative membrane potentials. Agonist-induced sensitisation may provide an explanation for sensitisation following long-term exposure to harmful irritants and pollutants, particularly in the airways. Abstract The TRPA1 ion channel is expressed in nociceptive (pain-sensitive) neurons and responds to a wide variety of chemical irritants, such as acrolein in smoke or isothiocyanates in mustard. Here we show that in the absence of extracellular calcium the current passing through TRPA1 gradually increases (sensitises) during prolonged application of agonists. Activation by an agonist is essential, because activation of TRPA1 by membrane depolarisation did not cause sensitisation. Sensitisation is independent of the site of action of the agonist, because covalent and non-covalent agonists were equally effective, and is long lasting following agonist removal. Mutating N-terminal cysteines, the target of covalent agonists, did not affect sensitisation by the non-covalent agonist carvacrol, which activates by binding to a different site. Sensitisation is unaffected by agents blocking ion channel trafficking or by block of signalling pathways involving ATP, protein kinase A or the formation of lipid rafts, and does not require ion flux through the channel. Examination of the voltage dependence of TRPA1 activation shows that sensitisation is accompanied by a slowly developing shift in the voltage dependence of TRPA1 towards more negative membrane potentials, and is therefore intrinsic to the TRPA1 channel. Sensitisation may play a role in exacerbating the pain caused by prolonged activation of TRPA1.

PLoS one 12(1), e0170097 (2017). doi:10.1371/journal.pone.0170097, Published by PLoS, Lawrence, Kan.

International journal of molecular sciences 20(18), 4572 (2019). doi:10.3390/ijms20184572 special issue: "Special Issue "Ion Channels of Nociception" / Special Issue Editor: Prof. Dr. Rashid Giniatullin, Guest Editor", Published by Molecular Diversity Preservation International, Basel

PLoS one 11(9), e0161789 (2016). doi:10.1371/journal.pone.0161789, Published by PLoS, Lawrence, Kan.

Migraine is a debilitating disorder of the CNS. Although therapeutic options for migraine attacks have tremendously advanced with the development of triptans more than a decade ago, several conditions (such as vascular disease) restrict their use. Moreover, some patients do not respond to triptans and other currently available medications. Therefore, treatment alternatives are needed. Study data show that 5-HT(1F) receptor agonists successfully abort migraine attacks. These data also suggest a favorable vascular side-effect profile of these substances, which could be beneficial for migraine treatment in subjects with cardiac or vascular disease. We discuss the current knowledge of 5-HT(1F) receptor-mediated effects, in part by comparing them to triptans, and we also summarize data from basic research and clinical trials.

Migraine is among the most prevalent headache disorders and results from dysfunctions within the trigeminovascular system (TVS). The inflammatory processes that have been suggested to occur in the cascade of events resulting in migraine sensitise trigeminal nociceptors, possibly causing hyperalgesia and allodynia. Trigeminal nociceptors express the heat- and capsaicin-gated channel TRPV1, which seems to play a significant role in the development of peripheral and central sensitisation and of hyperalgesia and allodynia. Here, we review the molecular mechanisms leading to the sensitisation of TRPV1 and attempt to link them to migraine-relevant pathophysiological processes. We argue that antagonising TRPV1 sensitisation is a promising approach and should receive more attention in future research as well as in the development of anti-migraine drugs.