Voltage-dependent Sodium Currents Research Articles

Disease-causing Slack potassium channel mutations produce opposite effects on excitability of excitatory and inhibitory neurons

The KCNT1 gene encodes the sodium-activated potassium channel Slack (KCNT1, KNa1.1), a regulator of neuronal excitability. Gain-of-function mutations in humans cause cortical network hyperexcitability, seizures, and severe intellectual disability. Using a mouse model expressing the Slack-R455H mutation, we find that Na+-dependent K+ (KNa) and voltage-dependent sodium (NaV) currents are increased in both excitatory and inhibitory cortical neurons. These increased currents, however, enhance the firing of excitability neurons but suppress that of inhibitory neurons. We further show that the expression of NaV channel subunits, particularly that of NaV1.6, is upregulated and that the length of the axon initial segment and of axonal NaV immunostaining is increased in both neuron types. Our study on the coordinate regulation of KNa currents and the expression of NaV channels may provide an avenue for understanding and treating epilepsies and other neurological disorders.

Fast voltage-dependent sodium (NaV ) currents are functionally expressed in mouse corpus cavernosum smooth muscle cells.

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 the voltage-dependent sodium (NaV ) currents in mouse CCSM and investigate their function. We used electrophysiological, pharmacological and immunocytochemical methods to study the NaV currents in isolated CCSM cells from C57BL/6 mice. Tension measurements were carried out using crural sections of the corpus cavernosum in whole tissue. Fast, voltage-dependent, sodium currents in mouse CCSM were 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 identified. TTX-sensitive currents showed 48% block with the NaV channel 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 currents were resistant to blockade by A803467, specific for NaV 1.8 channels. Immunocytochemistry confirmed expression of NaV 1.5 and NaV 1.4 in freshly dispersed CCSM cells. Veratridine, a NaV channel activator, reduced time-dependent inactivation of NaV currents and increased duration of evoked action potentials. Veratridine induced phasic contractions in CCSM strips, reversible with TTX and nifedipine but not KB-R7943. There are fast, voltage-dependent, sodium currents in mouse CCSM. Stimulation of these currents increased contractility of CCSM in vitro, suggesting an involvement in detumescence and potentially providing a clinically relevant target in erectile dysfunction. Further work will be necessary to define its role.

E44Q mutation in NaV1.7 in a patient with infantile paroxysmal knee pain: electrophysiological analysis of voltage-dependent sodium current

Gain-of-function mutations in voltage-gated sodium channels (NaV1.7, NaV1.8, and NaV1.9) are known causes of inherited pain disorders. Identification and functional assessment of new NaV1.7 mutations could help elucidate the phenotypic spectrum of NaV1.7 channelopathies. We identified a novel NaV1.7 mutation (E44Q in exon 2) that substitutes a glutamic acid residue for glutamine in the cytoplasmic N-terminus of NaV1.7 in a patient with paroxysmal pain attacks during childhood and his family who experienced similar pain episodes. To study the sodium channel's function, we performed electrophysiological recordings. Voltage-clamp recordings revealed that the mutation increased the amplitude of the non-inactivating component of the sodium current, which might facilitate channel opening. These data demonstrate that E44Q is a gain-of-function mutation in NaV1.7, which is consistent with our patient's pain phenotype.

SAR340835, a Novel Selective Na+/Ca2+ Exchanger Inhibitor, Improves Cardiac Function and Restores Sympathovagal Balance in Heart Failure.

In failing hearts, Na+/Ca2+ exchanger (NCX) overactivity contributes to Ca2+ depletion, leading to contractile dysfunction. Inhibition of NCX is expected to normalize Ca2+ mishandling, to limit afterdepolarization-related arrhythmias, and to improve cardiac function in heart failure (HF). SAR340835/SAR296968 is a selective NCX inhibitor for all NCX isoforms across species, including human, with no effect on the native voltage-dependent calcium and sodium currents in vitro. Additionally, it showed in vitro and in vivo antiarrhythmic properties in several models of early and delayed afterdepolarization-related arrhythmias. Its effect on cardiac function was studied under intravenous infusion at 250,750 or 1500 µg/kg per hour in dogs, which were either normal or submitted to chronic ventricular pacing at 240 bpm (HF dogs). HF dogs were infused with the reference inotrope dobutamine (10 µg/kg per minute, i.v.). In normal dogs, NCX inhibitor increased cardiac contractility (dP/dtmax) and stroke volume (SV) and tended to reduce heart rate (HR). In HF dogs, NCX inhibitor significantly and dose-dependently increased SV from the first dose (+28.5%, +48.8%, and +62% at 250, 750, and 1500 µg/kg per hour, respectively) while significantly increasing dP/dtmax only at 1500 (+33%). Furthermore, NCX inhibitor significantly restored sympathovagal balance and spontaneous baroreflex sensitivity (BRS) from the first dose and reduced HR at the highest dose. In HF dogs, dobutamine significantly increased dP/dtmax and SV (+68.8%) but did not change HR, sympathovagal balance, or BRS. Overall, SAR340835, a selective potent NCX inhibitor, displayed a unique therapeutic profile, combining antiarrhythmic properties, capacity to restore systolic function, sympathovagal balance, and BRS in HF dogs. NCX inhibitors may offer new therapeutic options for acute HF treatment. SIGNIFICANCE STATEMENT: HF is facing growing health and economic burden. Moreover, patients hospitalized for acute heart failure are at high risk of decompensation recurrence, and no current acute decompensated HF therapy definitively improved outcomes. A new potent, Na+/Ca2+ exchanger inhibitor SAR340835 with antiarrhythmic properties improved systolic function of failing hearts without creating hypotension, while reducing heart rate and restoring sympathovagal balance. SAR340835 may offer a unique and attractive pharmacological profile for patients with acute heart failure as compared with current inotrope, such as dobutamine.

Chronic resveratrol consumption prevents hypertension development altering electrophysiological currents and Ca2+ signaling in chromaffin cells from SHR rats

Resveratrol (RESV) is one of the most abundant polyphenol-stilbene compounds found in red wine with well-established cardioprotective and antihypertensive effects. Hyperactivity of the sympathoadrenal axis seems to be one of the major contributing factors in the pathogenesis of human essential hypertension. Alterations in outward voltage-dependent potassium currents (IK) and inward voltage-dependent sodium (INa), calcium (ICa) and nicotinic (IACh) currents, CCs excitability, Ca2+ homeostasis, and catecholamine exocytosis were previously related to the hypertensive state. This raised the issue of whether in vivo long-term RESV treatment can directly act as a modulator of Ca2+ influx or a regulator of ion channel permeability in CCs. We monitored outward and inward currents, and cytosolic Ca2+ concentrations ([Ca2+]c) using different pharmacological approaches in CCs from normotensive (WKY) and hypertensive (SHR) animals chronically exposed to trans-RESV (50 mg/L/v.o, 28 days). The long-term RESV treatment prevented the increase of the systolic blood pressure (SBP) in SHR, without reversion of cardiac hypertrophy. We also found an increase of the outward IK, reduction in inward INa,ICa, and IACh, and the mitigation of [Ca2+]c overload in CCs from SHR at the end of RESV treatment. Our data revealed that electrophysiological alterations of the CCs and in its Ca2+ homeostasis are potential new targets related to the antihypertensive effects of long-term RESV treatment.

Role of TTX-sensible voltage dependent sodium currents for the biological effects promoted by vitamin D3 in a model of neuronal differentiation

Role of TTX-sensible voltage dependent sodium currents for the biological effects promoted by vitamin D3 in a model of neuronal differentiation

TTX-resistant sodium currents in medial prefrontal cortex pyramidal neurons depend on extracellular Ca2+ concentration

Background: Previous reports reported the presence of TTX-resistant Nav1.8 and Nav1.9 sodium chan­nels in the cortex pyramidal neurons. A characteristic feature of Nav1.9 channels is activation at voltages close to — 70 mV. Therefore, they do not participate directly in the action potential but contribute to the regulation of the resting membrane potential. Their physiological role is modulation of cell excitability. The aim of the study was to investigate, with the use of patch clamp technique, the dependence of the activation thresholds of TTX–resistant sodium currents on the concentration of extracellular calcium in medial prefrontal cortex pyramidal neurons in rats. Results: The recorded values of the threshold of the voltage-dependent sodium currents were in the range of -65 mV to -75 mV. This suggests that the sodium currents may result from the presence of Nav1.9 channels in the rat pyramidal neurons. The threshold for the activation of sodium currents depended on the concentration of Ca2+. Increasing the concentration of calcium ions in the extracellular solution by 5 mM caused the depolarizing shift in the activation potential by about 10 mV. The effect of calcium ion concentration on the potential of TTX-resistant currents activation suggests that Nav1.9 channels are modulated by extracellular Ca2+ concentration. Conclusions: The study has experimentally confirmed that TTX-resistant channels are present in the cell membrane of the rat prefrontal cortex pyramidal neurons and may, therefore, take a physiological role in the conductivity of sodium currents in a manner dependent on the concentration of extracellular ions.

Sodium and potassium conductances in principal neurons of the mouse piriform cortex: a quantitative description.

The primary olfactory (or piriform) cortex is a promising model system for understanding how the cerebral cortex processes sensory information, although an investigation of the piriform cortex is hindered by a lack of detailed information about the intrinsic electrical properties of its component neurons. In the present study, we quantify the properties of voltage-dependent sodium currents and voltage- and calcium-dependent potassium currents in two important classes of excitatory neurons in the main input layer of the piriform cortex. We identify several classes of these currents and show that their properties are similar to those found in better-studied cortical regions. Our detailed quantitative descriptions of these currents will be valuable to computational neuroscientists who aim to build models that explain how the piriform cortex encodes odours. The primary olfactory cortex (or piriform cortex, PC) is an anatomically simple palaeocortex that is increasingly used as a model system for investigating cortical sensory processing. However, little information is available on the intrinsic electrical conductances in neurons of the PC, hampering efforts to build realistic computational models of this cortex. In the present study, we used nucleated macropatches and whole-cell recordings to rigorously quantify the biophysical properties of voltage-gated sodium (NaV ), voltage-gated potassium (KV ) and calcium-activated potassium (KCa ) conductances in two major classes of glutamatergic neurons in layer 2 of the PC, semilunar (SL) cells and superficial pyramidal (SP) cells. We found that SL and SP cells both express a fast-inactivating NaV current, two types of KV current (A-type and delayed rectifier-type) and three types of KCa current (fast-, medium- and slow-afterhyperpolarization currents). The kinetic and voltage-dependent properties of the NaV and KV conductances were, with some exceptions, identical in SL and SP cells and similar to those found in neocortical pyramidal neurons. The KCa conductances were also similar across the different types of neurons. Our results are summarized in a series of empirical equations that should prove useful to computational neuroscientists seeking to model the PC. More broadly, our findings indicate that, at the level of single-cell electrical properties, this palaeocortex is not so different from the neocortex, vindicating efforts to use the PC as a model of cortical sensory processing in general.

Inhibitory effects of cannabidiol on voltage-dependent sodium currents

Cannabis sativa contains many related compounds known as phytocannabinoids. The main psychoactive and nonpsychoactive compounds are Δ9-tetrahydrocannabinol (THC) and cannabidiol (CBD), respectively. Much of the evidence for clinical efficacy of CBD-mediated antiepileptic effects has been from case reports or smaller surveys. The mechanisms for CBD's anticonvulsant effects are unclear and likely involve noncannabinoid receptor pathways. CBD is reported to modulate several ion channels, including sodium channels (Nav). Evaluating the therapeutic mechanisms and safety of CBD demands a richer understanding of its interactions with central nervous system targets. Here, we used voltage-clamp electrophysiology of HEK-293 cells and iPSC neurons to characterize the effects of CBD on Nav channels. Our results show that CBD inhibits hNav1.1–1.7 currents, with an IC50 of 1.9–3.8 μm, suggesting that this inhibition could occur at therapeutically relevant concentrations. A steep Hill slope of ∼3 suggested multiple interactions of CBD with Nav channels. CBD exhibited resting-state blockade, became more potent at depolarized potentials, and also slowed recovery from inactivation, supporting the idea that CBD binding preferentially stabilizes inactivated Nav channel states. We also found that CBD inhibits other voltage-dependent currents from diverse channels, including bacterial homomeric Nav channel (NaChBac) and voltage-gated potassium channel subunit Kv2.1. Lastly, the CBD block of Nav was temperature-dependent, with potency increasing at lower temperatures. We conclude that CBD's mode of action likely involves 1) compound partitioning in lipid membranes, which alters membrane fluidity affecting gating, and 2) undetermined direct interactions with sodium and potassium channels, whose combined effects are loss of channel excitability.

Smn-Deficiency Increases the Intrinsic Excitability of Motoneurons.

During development, motoneurons experience significant changes in their size and in the number and strength of connections that they receive, which requires adaptive changes in their passive and active electrical properties. Even after reaching maturity, motoneurons continue to adjust their intrinsic excitability and synaptic activity for proper functioning of the sensorimotor circuit in accordance with physiological demands. Likewise, if some elements of the circuit become dysfunctional, the system tries to compensate for the alterations to maintain appropriate function. In Spinal Muscular Atrophy (SMA), a severe motor disease, spinal motoneurons receive less excitation from glutamatergic sensory fibers and interneurons and are electrically hyperexcitable. Currently, the origin and relationship among these alterations are not completely established. In this study, we investigated whether Survival of Motor Neuron (SMN), the ubiquitous protein defective in SMA, regulates the excitability of motoneurons before and after the establishment of the synaptic contacts. To this end, we performed patch-clamp recordings in embryonic spinal motoneurons forming complex synaptic networks in primary cultures, and in differentiated NSC-34 motoneuron-like cells in the absence of synaptic contacts. Our results show that in both conditions, Smn-deficient cells displayed lower action potential threshold, greater action potential amplitudes, and larger density of voltage-dependent sodium currents than cells with normal Smn-levels. These results indicate that Smn participates in the regulation of the cell-autonomous excitability of motoneurons at an early stage of development. This finding may contribute to a better understanding of motoneuron excitability in SMA during the development of the disease.

A Negative Slope Conductance of the Persistent Sodium Current Prolongs Subthreshold Depolarizations

Neuronal subthreshold voltage-dependent currents determine membrane properties such as the input resistance (Rin) and the membrane time constant (τm) in the subthreshold range. In contrast with classical cable theory predictions, the persistent sodium current (INaP), a non-inactivating mode of the voltage-dependent sodium current, paradoxically increases Rin and τm when activated. Furthermore, this current amplifies and prolongs synaptic currents in the subthreshold range. Here, using a computational neuronal model, we showed that the creation of a region of negative slope conductance by INaP activation is responsible for these effects and the ability of the negative slope conductance to amplify and prolong Rin and τm relies on the fast activation of INaP. Using dynamic clamp in hippocampal CA1 pyramidal neurons in brain slices, we showed that the effects of INaP on Rin and τm can be recovered by applying an artificial INaP after blocking endogenous INaP with tetrodotoxin. Furthermore, we showed that injection of a pure negative conductance is enough to reproduce the effects of INaP on Rin and τm and is also able to prolong artificial excitatory post synaptic currents. Since both the negative slope conductance and the almost instantaneous activation are critical for producing these effects, the INaP is an ideal current for boosting the amplitude and duration of excitatory post synaptic currents near the action potential threshold.

Electrophysiological assessment of primary cortical neurons genetically engineered using iron oxide nanoparticles

The development of safe technologies to genetically modify neurons is of great interest in regenerative neurology, for both translational and basic science applications. Such approaches have conventionally been heavily reliant on viral transduction methods, which have safety and production limitations. Magnetofection (magnet-assisted gene transfer using iron oxide nanoparticles as vectors) has emerged as a highly promising non-viral alternative for safe and reproducible genetic modification of neurons. Despite the high potential of this technology, there is an important gap in our knowledge of the safety of this approach, namely, whether it alters neuronal function in adverse ways, such as by altering neuronal excitability and signaling. We have investigated the effects of magnetofection in primary cortical neurons by examining neuronal excitability using the whole cell patch clamp technique. We found no evidence that magnetofection alters the voltage-dependent sodium and potassium ionic currents that underpin excitability. Our study provides important new data supporting magnetofection as a safe technology for bioengineering of neuronal cell populations. Open image in new window

Molecular Pathophysiology of Congenital Long QT Syndrome.

Ion channels represent the molecular entities that give rise to the cardiac action potential, the fundamental cellular electrical event in the heart. The concerted function of these channels leads to normal cyclical excitation and resultant contraction of cardiac muscle. Research into cardiac ion channel regulation and mutations that underlie disease pathogenesis has greatly enhanced our knowledge of the causes and clinical management of cardiac arrhythmia. Here we review the molecular determinants, pathogenesis, and pharmacology of congenital Long QT Syndrome. We examine mechanisms of dysfunction associated with three critical cardiac currents that comprise the majority of congenital Long QT Syndrome cases: 1) IKs, the slow delayed rectifier current; 2) IKr, the rapid delayed rectifier current; and 3) INa, the voltage-dependent sodium current. Less common subtypes of congenital Long QT Syndrome affect other cardiac ionic currents that contribute to the dynamic nature of cardiac electrophysiology. Through the study of mutations that cause congenital Long QT Syndrome, the scientific community has advanced understanding of ion channel structure-function relationships, physiology, and pharmacological response to clinically employed and experimental pharmacological agents. Our understanding of congenital Long QT Syndrome continues to evolve rapidly and with great benefits: genotype-driven clinical management of the disease has improved patient care as precision medicine becomes even more a reality.

A potent and selective small molecule inhibitor of sirtuin 1 promotes differentiation of pluripotent P19 cells into functional neurons.

Sirtuin 1 (SIRT1) is known to suppress differentiation of pluripotent/multipotent cells and neural progenitor cells into neurons by blocking activation of transcription factors critical for neurogenesis. EX-527 is a highly selective and potent inhibitor against SIRT1 and has been used as a chemical probe that modulates SIRT1-associated biological processes. However, the effect of EX-527 on neuronal differentiation in pluripotent cells has not been well elucidated. Here, we report an examination of EX-527 effects on neurogenesis of pluripotent P19 cells. The results showed that EX-527 greatly accelerated differentiation of P19 cells into neurons without generation of cardiac cells and astrocytes. Importantly, neurons derived from P19 cells treated with EX-527 generated voltage-dependent sodium currents and depolarization-induced action potentials. The findings indicate that the differentiated cells have electrophysiological properties. The present study suggests that the selective SIRT1 inhibitor could have the potential of being employed as a chemical inducer to generate functionally active neurons.

Altered Sodium and Potassium, but not Calcium Currents in Cerebellar Granule Cells in an In Vitro Model of Neuronal Injury.

Acute injury of central nervous system (CNS) starts a cascade of morphological, molecular, and functional changes including formation of a fibrotic scar, expression of transforming growth factor beta 1 (TGF-β1), and expression of extracellular matrix proteins leading to arrested neurite outgrowth and failed regeneration. We assessed alteration of electrophysiological properties of cerebellar granule cells (CGCs) in two in vitro models of neuronal injury: (i) model of fibrotic scar created from coculture of meningeal fibroblasts and cerebral astrocytes with addition of TGF-β1; (ii) a simplified model based on administration of TGF-β1 to CGCs culture. Both models reproduced suppression of neurite outgrowth caused by neuronal injury, which was equally restored by chondroitinase ABC (ChABC), a key disruptor of fibrotic scar formation. Voltage-dependent calcium current was not affected in either injury model. However, intracellular calcium concentration could be altered as an expression of inositol trisphosphate receptor type 1 was suppressed by TGF-β1 and restored by ChABC. Voltage-dependent sodium current was significantly suppressed in CGCs cultured on a model of fibrotic scar and was only partly restored by ChABC. Administration of TGF-β1 significantly shifted current-voltage relation of sodium current toward more positive membrane potential without change to maximal current amplitude. Both transient and sustained potassium currents were significantly suppressed on a fibrotic scar and restored by ChABC to their control amplitudes. In contrast, TGF-β1 itself significantly upregulated transient and did not change sustained potassium current. Observed changes of voltage-dependent ion currents may contribute to known morphological and functional changes in injured CNS.

Photocontrol of Voltage-Gated Ion Channel Activity by Azobenzene Trimethylammonium Bromide in Neonatal Rat Cardiomyocytes.

The ability of azobenzene trimethylammonium bromide (azoTAB) to sensitize cardiac tissue excitability to light was recently reported. The dark, thermally relaxed trans- isomer of azoTAB suppressed spontaneous activity and excitation propagation speed, whereas the cis- isomer had no detectable effect on the electrical properties of cardiomyocyte monolayers. As the membrane potential of cardiac cells is mainly controlled by activity of voltage-gated ion channels, this study examined whether the sensitization effect of azoTAB was exerted primarily via the modulation of voltage-gated ion channel activity. The effects of trans- and cis- isomers of azoTAB on voltage-dependent sodium (INav), calcium (ICav), and potassium (IKv) currents in isolated neonatal rat cardiomyocytes were investigated using the whole-cell patch-clamp technique. The experiments showed that azoTAB modulated ion currents, causing suppression of sodium (Na+) and calcium (Ca2+) currents and potentiation of net potassium (K+) currents. This finding confirms that azoTAB-effect on cardiac tissue excitability do indeed result from modulation of voltage-gated ion channels responsible for action potential.

Elevated Neuronal Excitability Due to Modulation of the Voltage-Gated Sodium Channel Nav1.6 by Aβ1-42.

Aberrant increases in neuronal network excitability may contribute to the cognitive deficits in Alzheimer's disease (AD). However, the mechanisms underlying hyperexcitability are not fully understood. Such overexcitation of neuronal networks has been detected in the brains of APP/PS1 mice. In the present study, using current-clamp recording techniques, we observed that 12 days in vitro (DIV) primary cultured pyramidal neurons from P0 APP/PS1 mice exhibited a more prominent action potential burst and a lower threshold than WT littermates. Moreover, after treatment with Aβ1−42 peptide, 12 DIV primary cultured neurons showed similar changes, to a greater degree than in controls. Voltage-clamp recordings revealed that the voltage-dependent sodium current density of neurons incubated with Aβ1−42 was significantly increased, without change in the voltage-dependent sodium channel kinetic characteristics. Immunohistochemistry and western blot results showed that, after treatment with Aβ1−42, expressions of Nav and Nav1.6 subtype increased in cultured neurons or APP/PS1 brains compared to control groups. The intrinsic neuronal hyperexcitability of APP/PS1 mice might thus be due to an increased expression of voltage-dependent sodium channels induced by Aβ1−42. These results may illuminate the mechanism of aberrant neuronal networks in AD.

PAC1R agonist maxadilan enhances hADSC viability and neural differentiation potential.

Pituitary adenylate cyclase‐activating polypeptide (PACAP) is a structurally endogenous peptide with many biological roles. However, little is known about its presence or effects in human adipose‐derived stem cells (hADSCs). In this study, the expression of PACAP type I receptor (PAC1R) was first confirmed in hADSCs. Maxadilan, a specific agonist of PAC1R, could increase hADSC proliferation as determined by Cell Counting Kit‐8 and cell cycle analysis and promote migration as shown in wound‐healing assays. Maxadilan also showed anti‐apoptotic activity in hADSCs against serum withdrawal‐induced apoptosis based on Annexin V/propidium iodide analysis and mitochondrial membrane potential assays. The anti‐apoptotic effects of maxadilan correlated with the down‐regulation of Cleaved Caspase 3 and Caspase 9 as well as up‐regulation of Bcl‐2. The chemical neural differentiation potential could be enhanced by maxadilan as indicated through quantitative PCR, Western blot and cell morphology analysis. Moreover, cytokine neural redifferentiation of hADSCs treated with maxadilan acquired stronger neuron‐like functions with higher voltage‐dependent tetrodotoxin‐sensitive sodium currents, higher outward potassium currents and partial electrical impulses as determined using whole‐cell patch clamp recordings. Maxadilan up‐regulated the Wnt/β‐catenin signalling pathway associated with dimer‐dependent activity of PAC1R, promoting cell viability that was inhibited by XAV939, and it also activated the protein kinase A (PKA) signalling pathway associated with ligand‐dependent activity of PAC1R, enhancing cell viability and neural differentiation potential that was inhibited by H‐89. In summary, these results demonstrated that PAC1R is present in hADSCs, and maxadilan could enhance hADSC viability and neural differentiation potential in neural differentiation medium.

Α-Dendrotoxin-sensitive Kv1 channels contribute to conduction failure of polymodal nociceptive C-fibers from rat coccygeal nerve.

It is known that some patients with diabetic neuropathy are usually accompanied by abnormal painful sensations. Evidence has accumulated that diabetic neuropathic pain is associated with the hyperexcitability of peripheral nociceptors. Previously, we demonstrated that reduced conduction failure of polymodal nociceptive C-fibers and enhanced voltage-dependent sodium currents of small dorsal root ganglion (DRG) neurons contribute to diabetic hyperalgesia. To further investigate whether and how potassium channels are involved in the conduction failure, α-dendrotoxin (α-DTX), a selective blocker of the low-threshold sustained Kv1 channel, was chosen to examine its functional capability in modulating the conduction properties of polymodal nociceptive C-fibers and the excitability of sensory neurons. We found that α-DTX reduced the conduction failure of C-fibers from coccygeal nerve in vivo accompanied by an increased initial conduction velocity but a decreased activity-dependent slowing of conduction velocity. In addition, the number of APs evoked by step currents was significantly enhanced after the treatment with α-DTX in small-diameter sensory neurons. Further study of the mechanism indicates α-DTX-sensitive K(+) current significantly reduced and the activation of this current in peak and steady state shifted to depolarization for diabetic neurons. Expression of Kv channel subunits Kv1.2 and Kv1.6 was downregulated in both small dorsal root ganglion neurons and peripheral C-fibers. Taken together, these results suggest that α-DTX-sensitive Kv1 channels might play an important role in regulating the conduction properties of polymodal nociceptive C-fibers and firing properties of sensory neurons.

Drug-induced shift in voltage-dependent sodium current activation explains rat-specific proarrhythmia in an oncology drug

Drug-induced shift in voltage-dependent sodium current activation explains rat-specific proarrhythmia in an oncology drug