Biomedical subjects

Sulayman D Dib-Hajj

Publications and source records attributed to Sulayman D Dib-Hajj.

At least 19 recordsLinked to original sources

PubMed2006

Na(V)1.7 mutant A863P in erythromelalgia: effects of altered activation and steady-state inactivation on excitability of nociceptive dorsal root ganglion neurons.

Inherited erythromelalgia/erythermalgia (IEM) is a neuropathy characterized by pain and redness of the extremities that is triggered by warmth. IEM has been associated with missense mutations of the voltage-gated sodium channel Na(V)1.7, which is preferentially expressed in most nociceptive dorsal root ganglia (DRGs) and sympathetic ganglion neurons. Several mutations occur in cytoplasmic linkers of Na(V)1.7, with only two mutations in segment 4 (S4) and S6 of domain I. We report here a simplex case with an alanine 863 substitution by proline (A863P) in S5 of domain II of Na(V)1.7. The functional effect of A863P was investigated by voltage-clamp analysis in human embryonic kidney 293 cells and by current-clamp analysis to determine the effects of A863P on firing properties of small DRG neurons. Activation of mutant channels was shifted by -8 mV, whereas steady-state fast inactivation was shifted by +10 mV, compared with wild-type (WT) channels. There was a marked decrease in the rate of deactivation of mutant channels, and currents elicited by slow ramp depolarizations were 12 times larger than for WT. These results suggested that A863P could render DRG neurons hyperexcitable. We tested this hypothesis by studying properties of rat DRG neurons transfected with either A863P or WT channels. A863P depolarized resting potential of DRG neurons by +6 mV compared with WT channels, reduced the threshold for triggering single action potentials to 63% of that for WT channels, and increased firing frequency of neurons when stimulated with suprathreshold stimuli. Thus, A863P mutant channels produce hyperexcitability in DRG neurons, which contributes to the pathophysiology of IEM.

Action Potentials↗

PubMed2006

Differential slow inactivation and use-dependent inhibition of Nav1.8 channels contribute to distinct firing properties in IB4+ and IB4- DRG neurons.

Nociceptive dorsal root ganglion (DRG) neurons can be classified into nonpeptidergic IB(4)(+) and peptidergic IB(4)(-) subtypes, which terminate in different layers in dorsal horn and transmit pain along different ascending pathways, and display different firing properties. Voltage-gated, tetrodotoxin-resistant (TTX-R) Na(v)1.8 channels are expressed in both IB(4)(+) and IB(4)(-) cells and produce most of the current underlying the depolarizing phase of action potential (AP). Slow inactivation of TTX-R channels has been shown to regulate repetitive DRG neuron firing behavior. We show in this study that use-dependent reduction of Na(v)1.8 current in IB(4)(+) neurons is significantly stronger than that in IB(4)(-) neurons, although voltage dependency of activation and steady-state inactivation are not different. The time constant for entry of Na(v)1.8 into slow inactivation in IB(4)(+) neurons is significantly faster and more Na(v)1.8 enter the slow inactivation state than in IB(4)(-) neurons. In addition, recovery from slow inactivation of Na(v)1.8 in IB(4)(+) neurons is slower than that in IB(4)(-) neurons. Using current-clamp recording, we demonstrate a significantly higher current threshold for generation of APs and a longer latency to onset of firing in IB(4)(+), compared with those of IB(4)(-) neurons. In response to a ramp stimulus, IB(4)(+) neurons produce fewer APs and display stronger adaptation, with a faster decline of AP peak than IB(4)(-) neurons. Our data suggest that differential use-dependent reduction of Na(v)1.8 current in these two DRG subpopulations, which results from their different rate of entry into and recovery from the slow inactivation state, contributes to functional differences between these two neuronal populations.

Action Potentials↗

PubMed2006

Size matters: Erythromelalgia mutation S241T in Nav1.7 alters channel gating.

The Nav1.7 sodium channel is preferentially expressed in most nociceptive dorsal root ganglion neurons and in sympathetic neurons. Inherited erythromelalgia (IEM, also known as erythermalgia), an autosomal dominant neuropathy characterized by burning pain in the extremities in response to mild warmth, has been linked to mutations in Nav1.7. Recently, a substitution of Ser-241 by threonine (S241T) in the domain I S4-S5 linker of Nav1.7 was identified in a family with IEM. To investigate the possible causative role of this mutation in the pathophysiology of IEM, we used whole-cell voltage-clamp analysis to study the effects of S241T on Nav1.7 gating in HEK293 cells. We found a hyperpolarizing shift of activation midpoint by 8.4 mV, an accelerated time to peak, slowing of deactivation, and an increase in the current in response to small, slow depolarizations. Additionally, S241T produced an enhancement of slow inactivation, shifting the midpoint by -12.3 mV. Because serine and threonine have similar biochemical properties, the S241T substitution suggested that the size of the side chain at this position affected channel gating. To test this hypothesis, we investigated the effect of S241A and S241L substitutions on the gating properties of Nav1.7. Although S241A did not alter the properties of the channel, S241L mimicked the effects of S241T. We conclude that the linker between S4 and S5 in domain I of Nav1.7 modulates gating of this channel, and that a larger side chain at position 241 interferes with its gating mechanisms.

Action Potentials↗

PubMed2006

Inherited erythermalgia: limb pain from an S4 charge-neutral Na channelopathy.

BACKGROUND: Inherited erythermalgia (also termed "erythromelalgia"), characterized by episodic burning pain in the distal extremities evoked by warmth, has been causally linked with mutations of the Na(v)1.7 sodium channel, which is preferentially expressed in nociceptors. Thus far, Na(v)1.7 mutations within intracellular linker parts of the channel have been physiologically characterized. OBJECTIVE: To investigate a Na(v)1.7 erythermalgia mutation that substitutes one uncharged amino acid for another within an S4 segment. METHODS: Whole-cell patch-clamp analysis was used to study biophysical properties of wild-type and mutant (F216S) Na(v)1.7 channels in mammalian cells. RESULTS: The F216S mutation hyperpolarizes the voltage dependence of activation by 11 mV, accelerates activation, slows deactivation, and enhances the response to slow, small depolarizations. CONCLUSION: These results provide a physiologic basis for the linkage to erythermalgia of an Na(v)1.7 mutation that substitutes one uncharged residue for another within an S4 segment of the channel. These changes should increase excitability of nociceptive dorsal root ganglion neurons in which the mutant channel is present, thus contributing to pain.

Action Potentials↗

PubMed2006

A single sodium channel mutation produces hyper- or hypoexcitability in different types of neurons.

Disease-producing mutations of ion channels are usually characterized as producing hyperexcitability or hypoexcitability. We show here that a single mutation can produce hyperexcitability in one neuronal cell type and hypoexcitability in another neuronal cell type. We studied the functional effects of a mutation of sodium channel Nav1.7 associated with a neuropathic pain syndrome, erythermalgia, within sensory and sympathetic ganglion neurons, two cell types where Nav1.7 is normally expressed. Although this mutation depolarizes resting membrane potential in both types of neurons, it renders sensory neurons hyperexcitable and sympathetic neurons hypoexcitable. The selective presence, in sensory but not sympathetic neurons, of the Nav1.8 channel, which remains available for activation at depolarized membrane potentials, is a major determinant of these opposing effects. These results provide a molecular basis for the sympathetic dysfunction that has been observed in erythermalgia. Moreover, these findings show that a single ion channel mutation can produce opposing phenotypes (hyperexcitability or hypoexcitability) in the different cell types in which the channel is expressed.

Animals↗

PubMed2006

Calmodulin regulates current density and frequency-dependent inhibition of sodium channel Nav1.8 in DRG neurons.

Sodium channel Nav1.8 produces a slowly inactivating, tetrodotoxin-resistant current, characterized by recovery from inactivation with fast and slow components, and contributes a substantial fraction of the current underlying the depolarizing phase of the action potential of dorsal root ganglion (DRG) neurons. Nav1.8 C-terminus carries a conserved calmodulin-binding isoleucine-glutamine (IQ) motif. We show here that calmodulin coimmunoprecipitates with endogenous Nav1.8 channels from native DRG, suggesting that the two proteins can interact in vivo. Treatment of native DRG neurons with a calmodulin-binding peptide (CBP) reduced the current density of Nav1.8 by nearly 65%, without changing voltage dependency of activation or steady-state inactivation. To investigate the functional role of CaM binding to the IQ motif in the Nav1.8 C-terminus, the IQ dipeptide was substituted by DE; we show that this impairs the binding of CaM to the IQ motif. Mutant Nav1.8IQ/DE channels produce currents with roughly 50% amplitude, but with unchanged voltage dependency of activation and inactivation when expressed in DRG neurons from Nav1.8-null mice. We also show that blocking the interaction of CaM and Nav1.8 using CBP or the IQ/DE substitution causes a buildup of inactivated channels and, in the case of the IQ/DE mutation, stimulation even at a low frequency of 0.1 Hz significantly enhances the frequency-dependent inhibition of the Nav1.8 current. This study presents, for the first time, evidence that calmodulin associates with a sodium channel, Nav1.8, in native neurons, and demonstrates a regulation of Nav1.8 currents that can significantly affect electrogenesis of DRG neurons in which Nav1.8 is normally expressed.

Action Potentials↗

PubMed2006

Sporadic onset of erythermalgia: a gain-of-function mutation in Nav1.7.

OBJECTIVE: Inherited erythermalgia (erythromelalgia) is an autosomal dominant disorder in which patients experience severe burning pain in the extremities, in response to mild thermal stimuli and exercise. Although mutations in sodium channel Na(v)1.7 have been shown to underlie erythermalgia in several multigeneration families with the disease that have been investigated to date, the molecular basis of erythermalgia in sporadic cases is enigmatic. We investigated the role of Na(v)1.7 in a sporadic case of erythermalgia in a Chinese family. METHODS: Genomic DNA from patients and their asymptomatic family members were sequenced to identify mutations in Na(v)1.7. Whole-cell patch clamp analysis was used to characterize biophysical properties of wild-type and mutant Na(v)1.7 channels in mammalian cells. RESULTS: A single amino acid substitution in the DIIS4-S5 linker of Na(v)1.7 was present in two children whose parents were asymptomatic. The asymptomatic father was genetically mosaic for the mutation. This mutation produces a hyperpolarizing shift in channel activation and an increase in amplitude of the response to slow, small depolarizations. INTERPRETATION: Founder mutations in Na(v)1.7, which can confer hyperexcitability on peripheral sensory neurons, can underlie sporadic erythermalgia.

Adolescent↗

PubMed2006

Differential modulation of sodium channel Na(v)1.6 by two members of the fibroblast growth factor homologous factor 2 subfamily.

FHF2A and FHF2B are two members of the fibroblast growth factor homologous factor 2 (FHF2) subfamily with distinct N termini. Using a generic antibody and electrophysiological methods, we previously showed that FHF2 is expressed in hippocampus and dorsal root ganglion (DRG) neurons and is colocalized with sodium channel Na(v)1.6 at sensory but not motor nodes of Ranvier, and that FHF2B associates with Na(v)1.6, causing an increase in current density and a small depolarizing shift in availability of channels. Using immunolabeling of adult rat tissue, we demonstrate that FHF2A is present within DRG but not in hippocampal or cerebellar neurons or at nodes of Ranvier in sciatic nerve, and that Na(v)1.6 and FHF2A are colocalized in nonmyelinated fibers. We also show that FHF2A binds directly to Na(v)1.6, and that the two proteins coimmunoprecipitate from transfected HEK293 cells. Because Na(v)1.6 has been associated with rapid firing rates, we examined the possible effects of FHF2B and the sister isoform, FHF2A, on electrophysiological properties of this channel in the DRG-derived ND7/23 cell line. We show that FHF2B inhibits accumulation of inactivation in response to trains of stimulation at high frequencies. In marked contrast, FHF2A causes an accumulation of inactivated channels at all frequencies tested due to a slowing of recovery from inactivation. Thus different FHF2 subfamily members have different functional effects on Na(v)1.6 and are differentially distributed in DRG neurons and their axons. This suggests that FHF2A and FHF2B may selectively alter firing behaviour of specific neuronal compartments via differential modulation of Na(v)1.6.

Cerebellum↗

PubMed2005

Voltage-gated sodium channel Nav1.6 is modulated by p38 mitogen-activated protein kinase.

Nav1.6 is the major sodium channel isoform at nodes of Ranvier in myelinated axons and, additionally, is distributed along unmyelinated C-fibers of sensory neurons. Thus, modulation of the sodium current produced by Nav1.6 might significantly impact axonal conduction. Mitogen-activated protein kinases (MAPKs) are expressed in neurons and are activated after injury, for example, after sciatic nerve transection and hypoxia. Although the role of MAPK in signal transduction and in injury-induced regulation of gene expression is well established, the ability of these kinases to phosphorylate and modulate voltage-gated sodium channels has not been reported. Sequence analysis shows that Nav1.6 contains a putative MAP kinase-recognition module in the cytoplasmic loop (L1), which joins domains 1 and 2. We show in this study that sodium channels and p38 MAP kinase colocalize in rat brain tissue and that activated p38alpha phosphorylates L1 of Nav1.6, specifically at serine 553 (S553), in vitro. None of the other cytoplasmic loops and termini of the channel are phosphorylated by activated p38alpha in these assays. Activation of p38 in the neuronal ND7/23 cell line transfected with Nav1.6 leads to a significant reduction in the peak Nav1.6 current amplitude, without a detectable effect on gating properties. The substitution of S553 with alanine within L1 of the Nav1.6 channel prevents p38-mediated reduction of Nav1.6 current density. This is the first demonstration of MAPK phosphorylation and modulation of a voltage-gated sodium channel, and this modulation may represent an additional role for MAPK in regulating the neuronal response to injury.

Amino Acid Substitution↗

PubMed2005

Pharmacological properties of neuronal TTX-resistant sodium channels and the role of a critical serine pore residue.

Voltage-gated sodium channels can be characterized by their sensitivity to inhibitors. Na(v)1.5 is sensitive to block by cadmium and extracellular QX-314, but relatively insensitive to tetrodotoxin and saxitoxin. Na(v)1.4 is tetrodotoxin- and saxitoxin-sensitive but resistant to cadmium and extracellular QX-314. Na(v)1.8 and Na(v)1.9 generate slowly inactivating (I(TTXr-Slow)) and persistent (I(TTXr-Per)) currents in sensory neurons that are tetrodotoxin-resistant. Tetrodotoxin sensitivity is largely determined by the identity of a single residue; tyrosine 401 in Na(v)1.4, cysteine 374 in Na(v)1.5 and serine 356 and 355 in Na(v)1.8 and Na(v)1.9. We asked whether Na(v)1.8 and Na(v)1.9 share other pharmacological properties as a result of this serine residue. I(TTXr-Slow) and I(TTXr-Per) were saxitoxin-resistant and resistant to internal QX-314. I(TTXr-Slow) was also resistant to external QX-314 and displayed a approximately fourfold higher sensitivity than I(TTXr-Per) to cadmium. The impact of the serine residue was investigated by replacing tyrosine 401 in Na(v)1.4 with serine (Y401S) or cysteine (Y401C). Both mutants were resistant to tetrodotoxin and saxitoxin. Whereas Na(v)1.4-Y401C displayed an increased sensitivity to cadmium and extracellular QX-314, the serine substitution did not alter the sensitivity of Na(v)1.4 to cadmium or QX-314. Our data indicates that while the serine residue determines the sensitivity of I(TTXr-Slow) and I(TTXr-Per) to tetrodotoxin and saxitoxin, it does not determine their insensitivity to QX-314 or their differential sensitivities to cadmium.

Animals↗

PubMed2005

Nav1.6 channels generate resurgent sodium currents in spinal sensory neurons.

The Na(v)1.6 voltage-gated sodium channel has been implicated in the generation of resurgent currents in cerebellar Purkinje neurons. Our data show that resurgent sodium currents are produced by some large diameter dorsal root ganglion (DRG) neurons from wild-type mice, but not from Na(v)1.6-null mice; small DRG neurons do not produce resurgent currents. Many, but not all, DRG neurons transfected with Na(v)1.6 produce resurgent currents. These results demonstrate for the first time the intrinsic ability of Na(v)1.6 to produce a resurgent current, and also show that cell background is critical in permitting the generation of these currents.

Animals↗

PubMed2005

Electrophysiological properties of two axonal sodium channels, Nav1.2 and Nav1.6, expressed in mouse spinal sensory neurones.

Sodium channels Na(v)1.2 and Na(v)1.6 are both normally expressed along premyelinated and myelinated axons at different stages of maturation and are also expressed in a subset of demyelinated axons, where coexpression of Na(v)1.6 together with the Na(+)/Ca(2+) exchanger is associated with axonal injury. It has been difficult to distinguish the currents produced by Na(v)1.2 and Na(v)1.6 in native neurones, and previous studies have not compared these channels within neuronal expression systems. In this study, we have characterized and directly compared Na(v)1.2 and Na(v)1.6 in a mammalian neuronal cell background and demonstrate differences in their properties that may affect neuronal behaviour. The Na(v)1.2 channel displays more depolarized activation and availability properties that may permit conduction of action potentials, even with depolarization. However, Na(v)1.2 channels show a greater accumulation of inactivation at higher frequencies of stimulation (20-100 Hz) than Na(v)1.6 and thus are likely to generate lower frequencies of firing. Na(v)1.6 channels produce a larger persistent current that may play a role in triggering reverse Na(+)/Ca(2+) exchange, which can injure demyelinated axons where Na(v)1.6 and the Na(+)/Ca(2+) exchanger are colocalized, while selective expression of Na(v)1.2 may support action potential electrogenesis, at least at lower frequencies, while producing a smaller persistent current.

Action Potentials↗

PubMed2005

Erythromelalgia: a hereditary pain syndrome enters the molecular era.

In contrast with acquired pain syndromes, molecular substrates for hereditary pain disorders have been poorly understood. Familial erythromelalgia (Weir Mitchell's disease), also known as primary erythermalgia, is an autosomal dominant disorder characterized by burning pain in the extremities in response to warm stimuli or moderate exercise. The cause of this disorder has been enigmatic, and treatment has been empirical and not very effective. Recent studies, however, have shown that familial erythromelalgia is a channelopathy caused by mutations in the gene encoding the Na(v)1.7 sodium channel which lead to altered channel function. Selective expression of Na(v)1.7 within dorsal root ganglion neurons including nociceptors (in which this channel is targeted to sensory terminals, close to impulse trigger zones) and within sympathetic ganglion neurons explains why patients experience pain but do not suffer from seizures or other manifestations of altered excitability within central nervous system neurons. Erythromelalgia is the first human disorder in which it has been possible to associate an ion channel mutation with chronic neuropathic pain. Identification of mutations within a peripheral neuron-specific sodium channel suggests the possibility of rational therapies that target the affected channel. Moreover, because some other pain syndromes, including acquired disorders, involve altered sodium channel function, erythromelalgia may emerge as a model disease that holds more general lessons about the molecular neurobiology of chronic pain.

Amino Acid Sequence↗

PubMed2005

CAP-1A is a novel linker that binds clathrin and the voltage-gated sodium channel Na(v)1.8.

The voltage-gated sodium channel Na(v)1.8 produces a tetrodotoxin-resistant current and plays a key role in nociception. Annexin II/p11 binds to Na(v)1.8 and facilitates insertion of the channel within the cell membrane. However, the mechanisms responsible for removal of specific channels from the cell membrane have not been studied. We have identified a novel protein, clathrin-associated protein-1A (CAP-1A), which contains distinct domains that bind Na(v)1.8 and clathrin. CAP-1A is abundantly expressed in DRG neurons and colocalizes with Na(v)1.8 and can form a multiprotein complex with Na(v)1.8 and clathrin. Coexpression of CAP-1A and Na(v)1.8 in DRG neurons reduces Na(v)1.8 current density by approximately 50% without affecting the endogenous or recombinant tetrodotoxin-sensitive currents. This effect of CAP-1A is blocked by bafilomycin A1 treatment of transfected DRG neurons. CAP-1A thus is the first example of an adapter protein that links clathrin and a sodium channel and may regulate Na(v)1.8 channel density at the cell surface.

Adaptor Proteins, Vesicular Transport↗

PubMed2005

Contactin regulates the current density and axonal expression of tetrodotoxin-resistant but not tetrodotoxin-sensitive sodium channels in DRG neurons.

Contactin, a glycosyl-phosphatidylinositol (GPI)-anchored predominantly neuronal cell surface glycoprotein, associates with sodium channels Nav1.2, Nav1.3 and Nav1.9, and enhances the density of these channels on the plasma membrane in mammalian expression systems. However, a detailed functional analysis of these interactions and of untested putative interactions with other sodium channel isoforms in mammalian neuronal cells has not been carried out. We examined the expression and function of sodium channels in small-diameter dorsal root ganglion (DRG) neurons from contactin-deficient (CNTN-/-) mice, compared to CNTN+/+ litter mates. Nav1.9 is preferentially expressed in isolectin B4 (IB4)-positive neurons and thus we used this marker to subdivide small-diameter DRG neurons. Using whole-cell patch-clamp recording, we observed a greater than two-fold reduction of tetrodotoxin-resistant (TTX-R) Nav1.8 and Nav1.9 current densities in IB4+ DRG neurons cultured from CNTN-/- vs. CNTN+/+ mice. Current densities for TTX-sensitive (TTX-S) sodium channels were unaffected. Contactin's effect was selective for IB4+ neurons as current densities for both TTX-R and TTX-S channels were not significantly different in IB4- DRG neurons from the two genotypes. Consistent with these results, we have demonstrated a reduction in Nav1.8 and Nav1.9 immunostaining on peripherin-positive unmyelinated axons in sciatic nerves from CNTN-/- mice but detected no changes in the expression for the two major TTX-S channels Nav1.6 and Nav1.7. These data provide evidence of a role for contactin in selectively regulating the cell surface expression and current densities of TTX-R but not TTX-S Na+ channel isoforms in nociceptive DRG neurons; this regulation could modulate the membrane properties and excitability of these neurons.

Animals↗

PubMed2004

Electrophysiological properties of mutant Nav1.7 sodium channels in a painful inherited neuropathy.

Although the physiological basis of erythermalgia, an autosomal dominant painful neuropathy characterized by redness of the skin and intermittent burning sensation of extremities, is not known, two mutations of Na(v)1.7, a sodium channel that produces a tetrodotoxin-sensitive, fast-inactivating current that is preferentially expressed in dorsal root ganglia (DRG) and sympathetic ganglia neurons, have recently been identified in patients with primary erythermalgia. Na(v)1.7 is preferentially expressed in small-diameter DRG neurons, most of which are nociceptors, and is characterized by slow recovery from inactivation and by slow closed-state inactivation that results in relatively large responses to small, subthreshold depolarizations. Here we show that these mutations in Na(v)1.7 produce a hyperpolarizing shift in activation and slow deactivation. We also show that these mutations cause an increase in amplitude of the current produced by Na(v)1.7 in response to slow, small depolarizations. These observations provide the first demonstration of altered sodium channel function associated with an inherited painful neuropathy and suggest that these physiological changes, which confer hyperexcitability on peripheral sensory and sympathetic neurons, contribute to symptom production in hereditary erythermalgia.

Amino Acid Substitution↗

PubMed2004

Contactin associates with sodium channel Nav1.3 in native tissues and increases channel density at the cell surface.

The upregulation of voltage-gated sodium channel Na(v)1.3 has been linked to hyperexcitability of axotomized dorsal root ganglion (DRG) neurons, which underlies neuropathic pain. However, factors that regulate delivery of Na(v)1.3 to the cell surface are not known. Contactin/F3, a cell adhesion molecule, has been shown to interact with and enhance surface expression of sodium channels Na(v)1.2 and Na(v)1.9. In this study we show that contactin coimmunoprecipitates with Na(v)1.3 from postnatal day 0 rat brain where this channel is abundant, and from human embryonic kidney (HEK) 293 cells stably transfected with Na(v)1.3 (HEK-Na(v)1.3). Purified GST fusion proteins of the N and C termini of Na(v)1.3 pull down contactin from lysates of transfected HEK 293 cells. Transfection of HEK-Na(v)1.3 cells with contactin increases the amplitude of the current threefold without changing the biophysical properties of the channel. Enzymatic removal of contactin from the cell surface of cotransfected cells does not reduce the elevated levels of the Na(v)1.3 current. Finally, we show that, similar to Na(v)1.3, contactin is upregulated in axotomized DRG neurons and accumulates within the neuroma of transected sciatic nerve. We propose that the upregulation of contactin and its colocalization with Na(v)1.3 in axotomized DRG neurons may contribute to the hyper-excitablity of the injured neurons.

Animals↗

PubMed2004

Functional role of the C-terminus of voltage-gated sodium channel Na(v)1.8.

Sodium channel Na(v)1.8 requires stronger depolarization than other sodium channels for activation and inactivation. The contribution of Na(v)1.8 C-terminus to this property was investigated by producing Na(v)1.8 and Na(v)1.4 chimeras and expressing them in ND7/23 cells. Current densities of the chimeras were significantly different than in parental channels, and the voltage-dependence of activation was depolarized in Na(v)1.4/1.8C compared to Na(v)1.4. Analysis of steady-state inactivation showed that only Na(v)1.8 and Na(v)1.4/1.8C currents demonstrate a non-inactivated fraction. Thus, the C-terminus of Na(v)1.8 contributes to regulation of channel density at the cell surface, modulates channel gating, and regulates the generation of sustained current.

Cell Line↗