Activation Of Voltage-gated Sodium Channels Research Articles

Partial block by riluzole of muscle sodium channels in myotubes from amyotrophic lateral sclerosis patients.

Denervated muscles undergo fibrillations due to spontaneous activation of voltage-gated sodium (Na+) channels generating action potentials. Fibrillations also occur in patients with amyotrophic lateral sclerosis (ALS). Riluzole, the only approved drug for ALS treatment, blocks voltage-gated Na+ channels, but its effects on muscle Na+ channels and fibrillations are yet poorly characterized. Using patch-clamp technique, we studied riluzole effect on Na+ channels in cultured myotubes from ALS patients. Needle electromyography was used to study fibrillation potentials (Fibs) in ALS patients during riluzole treatment and after one week of suspension. Patients were clinically characterized in all recording sessions. In myotubes, riluzole (1 μM, a therapeutic concentration) reduced Na+ current by 20%. The rate of rise and amplitude of spikes evoked by depolarizing stimuli were also reduced. Fibs were detected in all patients tested during riluzole treatment and riluzole washout had no univocal effect. Our study indicates that, in human myotubes, riluzole partially blocks Na+ currents and affects action potentials but does not prevent firing. In line with this in vitro finding, muscle Fibs in ALS patients appear to be largely unaffected by riluzole.

Nedd4-2 (NEDD4L) controls intracellular Na+-mediated activity of voltage-gated sodium channels in primary cortical neurons

Nedd4-2, a HECT (homologous with E6-associated protein C-terminus)-type ubiquitin protein ligase, has been implicated in regulating several ion channels, including Navs (voltage-gated sodium channels). In Xenopus oocytes Nedd4-2 strongly inhibits the activity of multiple Navs. However, the conditions under which Nedd4-2 mediates native Nav regulation remain uncharacterized. Using Nedd4-2-deficient mice, we demonstrate in the present study that in foetal cortical neurons Nedd4-2 regulates Navs specifically in response to elevated intracellular Na(+), but does not affect steady-state Nav activity. In dorsal root ganglia neurons from the same mice, however, Nedd4-2 does not control Nav activities. The results of the present study provide the first physiological evidence for an essential function of Nedd4-2 in regulating Navs in the central nervous system.

Sodium and potassium currents influence Wallerian degeneration of injured Drosophila axons.

Axons degenerate after injury and in neuropathies and disease via a self-destruction program whose mechanism is poorly understood. Axons that have lost connection to their cell bodies have altered electrical and synaptic activities, but whether such changes play a role in the axonal degeneration process is not clear. We have used a Drosophila model to study the Wallerian degeneration of motoneuron axons and their neuromuscular junction synapses. We found that degeneration of the distal nerve stump after a nerve crush is greatly delayed when there is increased potassium channel activity (by overexpression of two different potassium channels, Kir2.1 and dORKΔ-C) or decreased voltage-gated sodium channel activity (using mutations in the para sodium channel). Conversely, degeneration is accelerated when potassium channel activity is decreased (by expressing a dominant-negative mutation of Shaker). Despite the effect of altering voltage-gated sodium and potassium channel activity, recordings made after nerve crush demonstrated that the distal stump does not fire action potentials. Rather, a variety of lines of evidence suggest that the sodium and potassium channels manifest their effects upon degeneration through changes in the resting membrane potential, which in turn regulates the level of intracellular free calcium within the isolated distal axon.

The Function of Vacuolar ATPase (V-ATPase) a Subunit Isoforms in Invasiveness of MCF10a and MCF10CA1a Human Breast Cancer Cells

The vacuolar H(+) ATPases (V-ATPases) are ATP-driven proton pumps that transport protons across both intracellular and plasma membranes. Previous studies have implicated V-ATPases in the invasiveness of various cancer cell lines. In this study, we evaluated the role of V-ATPases in the invasiveness of two closely matched human breast cancer lines. MCF10a cells are a non-invasive, immortalized breast epithelial cell line, and MCF10CA1a cells are a highly invasive, H-Ras-transformed derivative of MCF10a cells selected for their metastatic potential. Using an in vitro Matrigel assay, MCF10CA1a cells showed a much higher invasion than the parental MCF10a cells. Moreover, this increased invasion was completely sensitive to the specific V-ATPase inhibitor concanamycin. MCF10CA1a cells expressed much higher levels of both a1 and a3 subunit isoforms relative to the parental line. Isoforms of subunit a are responsible for subcellular localization of V-ATPases, with a3 and a4 targeting V-ATPases to the plasma membrane of specialized cells. Knockdown of either a3 alone or a3 and a4 together using isoform-specific siRNAs inhibited invasion by MCF10CA1a cells. Importantly, overexpression of a3 but not the other a subunit isoforms greatly increased the invasiveness of the parental MCF10a cells. Similarly, overexpression of a3 significantly increased expression of V-ATPases at the plasma membrane. These studies suggest that breast tumor cells employ particular a subunit isoforms to target V-ATPases to the plasma membrane, where they function in tumor cell invasion.

Interleukin-6 inhibits voltage-gated sodium channel activity of cultured rat spinal cord neurons.

Interleukin-6 (IL-6) is a pleiotropic proinflammatory cytokine that plays a key role in the injuries and diseases of the central nervous system (CNS). A voltage-gated Na+ channel (VGSC) is essential for the excitability and electrical properties of the neurons. However, there is still limited information on the role of IL-6 in voltage-gated sodium channels. Our study aimed to investigate the effects of IL-6 on Na+ currents in cultured spinal-cord neurons. VGSC currents were activated and recorded using whole-cell patch-clamp technique in the cultured rat spinal cord neurons. The effects of IL-6 concentration and exposure duration were examined. To determine whether any change in the number of channels in the plasma membrane can inhibit IL-6 on VGSC currents, we examined the expression of α1A (SCN1α) subunit mRNA level and protein level in the neurons before and after IL-6 induction using real-time polymerase chain reaction. We verified that IL-6, through a receptor-mediated mechanism, suppressed Na+ currents in a time- and dose-dependent manner, but did not alter the voltage-dependent activation and inactivation. Gp130 was involved in this inhibition. Furthermore, the spike amplitude was also inhibited by IL-6 in the doses that decreased the Na+ currents. VGSC currents are significantly inhibited by IL-6. Our findings reveal that the potential neuroprotection of IL-6 may result from the inhibitory effects on VGSC currents.

Molecular Bases for the Asynchronous Activation of Sodium and Potassium Channels Required for Nerve Impulse Generation

Most action potentials are produced by the sequential activation of voltage-gated sodium (Nav) and potassium (Kv) channels. This is mainly achieved by the rapid conformational rearrangement of voltage-sensor (VS) modules in Nav channels, with activation kinetics up to 6-fold faster than Shaker-type Kv channels. Here, using mutagenesis and gating current measurements, we show that a 3-fold acceleration of the VS kinetics in Nav versus Shaker Kv channels is produced by the hydrophilicity of two "speed-control" residues located in the S2 and S4 segments in Nav domains I-III. An additional 2-fold acceleration of the Nav VS kinetics is provided by the coexpression of the β1 subunit, ubiquitously found in mammal tissues. This study uncovers the molecular bases responsible for the differential activation of Nav versus Kv channels, a fundamental prerequisite for the genesis of action potentials.

Two Alternative Conformations of a Voltage-Gated Sodium Channel

Activation and inactivation of voltage-gated sodium channels (Navs) are well studied, yet the molecular mechanisms governing channel gating in the membrane remain unknown. We present two conformations of a Nav from Caldalkalibacillus thermarum reconstituted into lipid bilayers in one crystal at 9Å resolution based on electron crystallography. Despite a voltage sensor arrangement identical with that in the activated form, we observed two distinct pore domain structures: a prominent form with a relatively open inner gate and a closed inner-gate conformation similar to the first prokaryotic Nav structure. Structural differences, together with mutational and electrophysiological analyses, indicated that widening of the inner gate was dependent on interactions among the S4–S5 linker, the N-terminal part of S5 and its adjoining part in S6, and on interhelical repulsion by a negatively charged C-terminal region subsequent to S6. Our findings suggest that these specific interactions result in two conformational structures.

Extracellular Protons Inhibit Charge Immobilization in the Cardiac Voltage-Gated Sodium Channel

Low pH depolarizes the voltage-dependence of cardiac voltage-gated sodium (NaV1.5) channel activation and fast inactivation and destabilizes the fast-inactivated state. The molecular basis for these changes in protein behavior has not been reported. We hypothesized that changes in the kinetics of voltage sensor movement may destabilize the fast-inactivated state in NaV1.5. To test this idea, we recorded NaV1.5 gating currents in Xenopus oocytes using a cut-open voltage-clamp with extracellular solution titrated to either pH 7.4 or pH 6.0. Reducing extracellular pH significantly depolarized the voltage-dependence of both the QON/V and QOFF/V curves, and reduced the total charge immobilized during depolarization. We conclude that destabilized fast-inactivation and reduced charge immobilization in NaV1.5 at low pH are functionally related effects.

Regulated Neuronal Neuromodulation via Spinal Cord Expression of the Gene for the Inwardly Rectifying Potassium Channel 2.1 (Kir2.1)

Neuromodulation is used to restore neural function in disorders that stem from an imbalance in the activity of specific neural networks when they prove refractory to pharmacological therapy. The Kir2.1 gene contributes to stabilizing the resting potential below the threshold of activation of voltage-gated sodium channels and action potentials. Therefore, the delivery of the Kir2.1 gene to neuronal cells could reduce the probability of action potential generation, inhibiting excessive neural activity. To address the hypothesis that overexpression of the inwardly rectifying potassium channel 2.1 (Kir2.1) gene could inhibit motor neuron activity and therefore be therapeutically used in gene-based neuromodulation. To induce expression of Kir2.1, the inducible RheoSwitch promoter was used and controlled by ligand. In vivo gene expression was accomplished by an adenoviral vector to deliver unilaterally into the lumbar spinal cord of rats. Behavioral assays demonstrated that neuromuscular inhibition was exclusive to rats that received the ligand. Histological analysis also showed evidence of some motor neuron loss in these animals. Behavioral effects of Kir2.1 expression were completely reversible, arguing that the behavioral effect did not result from motor neuron death. Delivery of the gene for Kir2.1 inhibits neurons by resisting depolarization to the action potential threshold. Regulated neuronal expression of Kir2.1 may provide an elegant means for neuromodulation in a selected neuronal population.

Expression of the sialyltransferase, ST3Gal4, impacts cardiac voltage-gated sodium channel activity, refractory period and ventricular conduction

The sequential glycosylation process typically ends with sialic acid residues added through trans-Golgi sialyltransferase activity. Individuals afflicted with congenital disorders of glycosylation often have reduced glycoprotein sialylation and present with multi-system symptoms including hypotonia, seizures, arrhythmia and cardiomyopathy. Cardiac voltage-gated Na+ channel (Nav) activity can be influenced by sialic acids likely contributing to an external surface potential causing channels to gate at less depolarized voltages. Here, a possible pathophysiological role for reduced sialylation is investigated by questioning the impact of gene deletion of the uniformly expressed beta-galactoside alpha-2,3-sialyltransferase 4 (ST3Gal4) on cardiac Nav activity, cellular refractory period and ventricular conduction. Whole-cell patch-clamp experiments showed that ventricular Nav from ST3Gal4 deficient mice (ST3Gal4−/−) gated at more depolarized potentials, inactivated more slowly and recovered from fast inactivation more rapidly than WT controls. Current-clamp recordings indicated a 20% increase in time to action potential peak and a 30ms decrease in ST3Gal4−/− myocyte refractory period, concurrent with increased Nav recovery rate. Nav expression, distribution and maximal Na+ current levels were unaffected by ST3Gal4 expression, indicating that reduced sialylation does not impact Nav surface expression and distribution. However, enzymatic desialylation suggested that ST3Gal4−/− ventricular Nav are less sialylated. Consistent with the shortened myocyte refractory period, epicardial conduction experiments using optical mapping techniques demonstrated a 27% reduction in minimum ventricular refractory period and increased susceptibility to arrhythmias in ST3Gal4−/− ventricles. Thus, deletion of a single sialyltransferase significantly impacts ventricular myocyte electrical signaling. These studies offer insight into diseases of glycosylation that are often associated with pathological changes in excitability and highlight the importance of glycosylation in cardiac physiology.

Molecular Determinants for the Genesis of the Action Potential

In nerves and muscles, action potentials are initiated by the rapid activation of voltage-gated sodium (Nav) channels and terminated by the delayed activation of voltage-gated potassium (Kv) channels. This sequential activation, which is the prerequisite for the genesis of the action potential, requires faster activation kinetics of the voltage-sensor domains (VSD) in Nav as compared to Kv channels. Despite on decades of investigations, the molecular determinants and mechanisms underlying this phenomenon remain elusive. Here, we show that this differential gating is mostly imparted by six conserved hydrophilic residues Thr or Ser located in the S2 and S4 segments of the VSD in domains I-III of Nav channels while these positions are commonly occupied by hydrophobic residues in the VSD of Kv channels. Hydrophilic substitutions at the S2 position in the Shaker Kv channel accelerate the gating charge transfer by decreasing its energy barrier while hydrophilic substitutions at the S4 position speed up VSD activation by destabilizing its resting conformation. Interestingly, these hydrophilic residues are present in a Nav-related gene expressed in an evolutionary-distant unicellular choanoflagellate, suggesting that rapidly-gated Nav channels evolved before the emergence of metazoans and their nervous systems. We also show that the physiological co-expression of the ubiquitous regulatory β1 subunit further accelerates VSD movement in both a neuronal and a muscular Nav, providing a molecular basis for the β1-dependent fast gating mode previously detected from the ionic conductance. Our study uncovers the fundamental molecular determinants and possible mechanisms that enabled the differential gating in sodium and potassium channels and the emergence of the action potential. This work was supported by NIH grant GM030376.

Scorpion beta-toxins and voltage-gated sodium channels: interactions and effects

Scorpion beta-toxins (beta-ScTxs) modify the activity of voltage-gated sodium (Nav) channels, thereby producing neurotoxic effects in diverse organisms. For this reason, beta-ScTxs are essential tools not only for discriminating among different channel sub-types but also for studying the mechanisms of channel gating and the structure-function relationship involved in this process. This review considers both the structural and the functional implications of the beta-ScTxs after they bind to their receptor sites, in accord with their classification into a) anti-mammalian beta-ScTxs, b) anti-insect selective excitatory beta-ScTxs, c) anti-insect selective depressant beta-ScTxs and d) beta-ScTxs active on both insect and mammals Navchannels. Additionally, the molecular mechanism of toxin action by the "voltage sensor trapping" model is discussed, and the systemic effects produced by these toxins are reviewed.

Bidirectional influence of sodium channel activation on NMDA receptor–dependent cerebrocortical neuron structural plasticity

Neuronal activity regulates brain development and synaptic plasticity through N-methyl-D-aspartate receptors (NMDARs) and calcium-dependent signaling pathways. Intracellular sodium ([Na(+)](i)) also exerts a regulatory influence on NMDAR channel activity, and [Na(+)](i) may, therefore, function as a signaling molecule. In an attempt to mimic the influence of neuronal activity on synaptic plasticity, we used brevetoxin-2 (PbTx-2), a voltage-gated sodium channel (VGSC) gating modifier, to manipulate [Na(+)](i) in cerebrocortical neurons. The acute application of PbTx-2 produced concentration-dependent increments in both intracellular [Na(+)] and [Ca(2+)]. Pharmacological evaluation showed that PbTx-2-induced Ca(2+) influx primarily involved VGSC activation and NMDAR-mediated entry. Additionally, PbTx-2 robustly potentiated NMDA-induced Ca(2+) influx. PbTx-2-exposed neurons showed enhanced neurite outgrowth, increased dendritic arbor complexity, and increased dendritic filopodia density. The appearance of spontaneous calcium oscillations, reflecting synchronous neuronal activity, was accelerated by PbTx-2 treatment. Parallel to this response, PbTx-2 increased cerebrocortical neuron synaptic density. PbTx-2 stimulation of neurite outgrowth, dendritic arborization, and synaptogenesis all exhibited bidirectional concentration-response profiles. This profile paralleled that of NMDA, which also produced bidirectional concentration-response profiles for neurite outgrowth and synaptogenesis. These data are consistent with the hypothesis that PbTx-2-enhanced neuronal plasticity involves NMDAR-dependent signaling. Our results demonstrate that PbTx-2 mimics activity-dependent neuronal structural plasticity in cerebrocortical neurons through an increase in [Na(+)](i), up-regulation of NMDAR function, and engagement of downstream Ca(2+)-dependent signaling pathways. These data suggest that VGSC gating modifiers may represent a pharmacologic strategy to regulate neuronal plasticity through NMDAR-dependent mechanisms.

Conotoxins Targeting Neuronal Voltage-Gated Sodium Channel Subtypes: Potential Analgesics?

Voltage-gated sodium channels (VGSC) are the primary mediators of electrical signal amplification and propagation in excitable cells. VGSC subtypes are diverse, with different biophysical and pharmacological properties, and varied tissue distribution. Altered VGSC expression and/or increased VGSC activity in sensory neurons is characteristic of inflammatory and neuropathic pain states. Therefore, VGSC modulators could be used in prospective analgesic compounds. VGSCs have specific binding sites for four conotoxin families: μ-, μO-, δ- and ί-conotoxins. Various studies have identified that the binding site of these peptide toxins is restricted to well-defined areas or domains. To date, only the μ- and μO-family exhibit analgesic properties in animal pain models. This review will focus on conotoxins from the μ- and μO-families that act on neuronal VGSCs. Examples of how these conotoxins target various pharmacologically important neuronal ion channels, as well as potential problems with the development of drugs from conotoxins, will be discussed.

Persistent Current Blockers of Voltage-Gated Sodium Channels: A Clinical Opportunity for Controlling Metastatic Disease

A range of experimental and clinical data suggests strongly (i) that metastatic progression in carcinomas is accompanied (maybe even preceded) by upregulation of functional voltage-gated sodium channels (VGSCs) and (ii) that VGSC activity enhances cancer cell invasiveness. First, this review outlines the available in vitro and in vivo evidence for the VGSC expression and its proposed pathophysiological role. Second, we question the mechanism(s) whereby VGSC activity can induce such a cancer-promoting effect. We advance the hypothesis that it is the hypoxia-sensitive persistent component of the VGSC current (INaP) that is central to the phenomenon. Indeed, blockers of INaP are very effective in suppressing cancer cell invasiveness in vitro. Based upon these data, UK and international patent applications have been filed which describe the use of INaP blockers, like ranolazine ("Ranexa") and riluzole ("Rilutex"), as anti-metastatic agents. Importantly, since these drugs are already in clinical use, against conditions like cardiac angina and amyotrophic lateral scelerosis, there are no issues of dosage, unacceptable side effects or long-term use. Thus, INaP blockers have the potential to turn cancer into a chronic condition.

Neuregulin Directly Decreases Voltage-Gated Sodium Current in Hippocampal ErbB4-Expressing Interneurons

The Neuregulin 1 (NRG1)/ErbB4 signaling pathway has been genetically and functionally implicated in the etiology underlying schizophrenia, and in the regulation of glutamatergic pyramidal neuron function and plasticity. However, ErbB4 receptors are expressed in subpopulations of GABAergic interneurons, but not in hippocampal or cortical pyramidal neurons, indicating that NRG1 effects on principal neurons are indirect. Consistent with these findings, NRG1 effects on hippocampal long-term potentiation at CA1 pyramidal neuron synapses in slices are mediated indirectly by dopamine. Here we studied whether NRG/ErbB signaling directly regulates interneuron intrinsic excitability by pharmacologically isolating ErbB4-expressing neurons in rat dissociated hippocampal cultures, which lack dopaminergic innervation. We found that NRG1 acutely attenuates ErbB4-expressing interneuron excitability by depolarizing the firing threshold; neurons treated with the pan-ErbB inhibitor PD158780 or negative for ErbB4 were unaffected. These effects of NRG1 are primarily attributable to decreased voltage-gated sodium channel activity, as current density was attenuated by ∼60%. In stark contrast, NRG1 had minor effects on whole-cell potassium currents. Our data reveal the direct actions of NRG1 signaling in ErbB4-expressing interneurons, and offer novel insight into how NRG1/ErbB4 signaling can impact hippocampal activity.

Neuronal expression of the ubiquitin ligase Nedd4-2 in rat dorsal root ganglia: Modulation in the spared nerve injury model of neuropathic pain

Neuronal hyperexcitability following peripheral nerve lesions may stem from altered activity of voltage-gated sodium channels (VGSCs), which gives rise to allodynia or hyperalgesia. In vitro, the ubiquitin ligase Nedd4-2 is a negative regulator of VGSC α-subunits (Nav), in particular Nav1.7, a key actor in nociceptor excitability. We therefore studied Nedd4-2 in rat nociceptors, its co-expression with Nav1.7 and Nav1.8, and its regulation in pathology. Adult rats were submitted to the spared nerve injury (SNI) model of neuropathic pain or injected with complete Freund’s adjuvant (CFA), a model of inflammatory pain. L4 dorsal root ganglia (DRG) were analyzed in sham-operated animals, seven days after SNI and 48h after CFA with immunofluorescence and Western blot. We observed Nedd4-2 expression in almost 50% of DRG neurons, mostly small and medium-sized. A preponderant localization is found in the non-peptidergic sub-population. Additionally, 55.7±2.7% and 55.0±3.6% of Nedd4-2-positive cells are co-labeled with Nav1.7 and Nav1.8 respectively. SNI significantly decreases the proportion of Nedd4-2-positive neurons from 45.9±1.9% to 33.5±0.7% (p<0.01) and the total Nedd4-2 protein to 44%±0.13% of its basal level (p<0.01, n=4 animals in each group, mean±SEM). In contrast, no change in Nedd4-2 was found after peripheral inflammation induced by CFA. These results indicate that Nedd4-2 is present in nociceptive neurons, is downregulated after peripheral nerve injury, and might therefore contribute to the dysregulation of Navs involved in the hyperexcitability associated with peripheral nerve injuries.

Enhanced excitability of guinea pig inferior mesenteric ganglion neurons during and following recovery from chemical colitis

Postganglionic sympathetic neurons in the prevertebral ganglia (PVG) provide ongoing inhibitory tone to the gastrointestinal tract and receive innervation from mechanosensory intestinofugal afferent neurons primarily located in the colon and rectum. This study tests the hypothesis that colitis alters the excitability of PVG neurons. Intracellular recording techniques were used to evaluate changes in the electrical properties of inferior mesenteric ganglion (IMG) neurons in the trinitrobenzene sulfonic acid (TNBS) and acetic acid models of guinea pig colitis. Visceromotor IMG neurons were hyperexcitable 12 and 24 h, but not 6 h, post-TNBS during "acute" inflammation. Hyperexcitability persisted at 6 days post-TNBS during "chronic" inflammation, as well as at 56 days post-TNBS when colitis had resolved. In contrast, there was only a modest decrease in the current required to elicit an action potential at 24 h after acetic acid administration. Vasomotor neurons from inflamed preparations exhibited normal excitability. The excitatory effects of XE-991, a blocker of the channel that contributes to the M-type potassium current, and heteropodatoxin-2, a blocker of the channel that contributes to the A-type potassium current, were unchanged in TNBS-inflamed preparations, suggesting that these currents did not contribute to hyperexcitability. Riluzole, an inhibitor of persistent sodium currents, caused tonic visceromotor neurons to accommodate to sustained current pulses, regardless of the inflammatory state of the preparation, and restored a normal rheobase in neurons from TNBS-inflamed preparations but did not alter the rheobase of control preparations, suggesting that enhanced activity of voltage-gated sodium channels may contribute to colitis-induced hyperexcitability. Collectively, these data indicate that enhanced sympathetic drive as a result of hyperexcitable visceromotor neurons may contribute to small bowel dysfunction during colitis.

Neurological perspectives on voltage-gated sodium channels

The activity of voltage-gated sodium channels has long been linked to disorders of neuronal excitability such as epilepsy and chronic pain. Recent genetic studies have now expanded the role of sodium channels in health and disease, to include autism, migraine, multiple sclerosis, cancer as well as muscle and immune system disorders. Transgenic mouse models have proved useful in understanding the physiological role of individual sodium channels, and there has been significant progress in the development of subtype selective inhibitors of sodium channels. This review will outline the functions and roles of specific sodium channels in electrical signalling and disease, focusing on neurological aspects. We also discuss recent advances in the development of selective sodium channel inhibitors.

A distinct de novo expression of Nav1.5 sodium channels in human atrial fibroblasts differentiated into myofibroblasts

Fibroblasts play a major role in heart physiology. They are at the origin of the extracellular matrix renewal and production of various paracrine and autocrine factors. In pathological conditions, fibroblasts proliferate, migrate and differentiate into myofibroblasts leading to cardiac fibrosis. This differentiated status is associated with changes in expression profile leading to neo-expression of proteins such as ionic channels. The present study investigates further electrophysiological changes associated with fibroblast differentiation focusing on the activity of voltage-gated sodium channels in human atrial fibroblasts and myofibroblasts. Using the patch clamp technique we show that human atrial myofibroblasts display a fast inward voltage gated sodium current with a density of 13.28 ± 2.88 pA pF(-1) whereas no current was detectable in non-differentiated fibroblasts. Quantitative RT-PCR reveals a large amount of transcripts encoding the Na(v)1.5 α-subunit with a fourfold increased expression level in myofibroblasts when compared to fibroblasts. Accordingly, half of the current was blocked by 1 μm of tetrodotoxin and immunocytochemistry experiments reveal the presence of Na(v)1.5 proteins. Overall, this current exhibits similar biophysical characteristics to sodium currents found in cardiac myocytes except for the window current that is enlarged for potentials between -100 and -20 mV. Since fibrosis is one of the fundamental mechanisms implicated in atrial fibrillation, it is of great interest to investigate how this current could influence myofibroblast properties. Moreover, since several Na(v)1.5 mutations are related to cardiac pathologies, this study offers a new avenue on the fibroblasts involvement of these mutations.