Sodium Channel Alpha Subunit Research Articles

A novel Ile1455Thr variant in the skeletal muscle sodium channel alpha-subunit in a patient with a severe adult-onset proximal myopathy with electrical myotonia and a patient with mild paramyotonia phenotype

In sodium channelopathies, a severe fixed myopathy caused by a dominant mutation is rare. We describe two unrelated patients with a novel variant, p.Ile1455Thr, with phenotypes of paramyotonia in one case and fixed proximal myopathy with latent myotonia in another. In-vitro whole cell patch-clamp studies show that the mutation slows inactivation and accelerates recovery, in line with other paramyotonia variants with destabilized fast inactivation as pathomechanism. Additionally, p.IleI1455 causes a loss-of-function by reduced membrane insertion, right-shift of activation, and slowed kinetics. Molecular dynamics simulations comparing wild type and mutant Nav1.4 showed that threonine substitution hindered D4S4 mobility in response to membrane depolarization, consistent with effects of the mutation on channel inactivation. The fixed myopathy is likely to be associated to gain-of-function leading to sodium accumulation, regional edema, T-tubular swelling and mitochondrial stress. A possible contribution of the loss-of-function features towards myotonia and myopathy is discussed.

Dravet Syndrome: Diagnosis and Long-Term Course.

Dravet syndrome is one of the most severe epilepsy syndromes of early childhood, and it comes with very high morbidity and mortality. The typical presentation is characterized by hemiclonic or generalized clonic seizures triggered by fever during the first year of life, followed by myoclonic, absence, focal and generalized tonic-clonic seizures. Non-convulsive status epilepticus and epileptic encephalopathy are common. Development is normal in the first year of life, but most individuals eventually suffer from intellectual impairment. Dravet syndrome is associated with mutations in the sodium channel alpha1 subunit gene (SCN1A) in 70-80% of individuals. SCN1A mutation results in inhibition of the GABAergic inhibitory interneurons, leading to excessive neuronal excitation. The "interneuron hypothesis" is the current most accepted pathophysiological mechanism of Dravet syndrome. The mortality rate is increased significantly in Dravet syndrome. Ataxia, a characteristic crouched gait and Parkinson's symptoms may develop in some individuals. It is likely that Dravet syndrome is underdiagnosed in adults with treatment-resistant epilepsy. Early diagnosis is important to avoid anti-seizure medications that exacerbate seizures.

Abstract 14602: Physical and Biophysical Coupling of the Cardiac Sodium Channel Involves 14-3-3

Introduction: Mutations in SCN5A, the gene encoding for the cardiac sodium channel, produce alterations of the cardiac action potential that lead to life-threatening arrhythmias such as Long QT Syndrome (LQT3) and Brugada Syndrome (BrS). The conventional wisdom that sodium channels exist in complexes containing a single alpha-subunit has been challenged by the existence of dominant-negative (DN) mutations in BrS and the presence of polymorphisms that can restore trafficking and gating deficiencies of mutant channels in LQT and BrS. In fact, we have previously demonstrated that SCN5A subunits can interact with each other. Here we hypothesized that the physical and biophysical interactions between SCN5A alpha-subunits involve the partner protein 14-3-3, known to form dimers. Methods: SCN5A DN-BrS mutants and LQT3 gating deficient mutants were expressed in HEK293 cells and in commercially available iPS-derived cardiomyocytes, iCells©, in presence or absence of 14-3-3 inhibition. Resulting currents were measured using patch-clamp. Results: In order to investigate if the DN-effect seen by some BrS mutants is due to interaction of the sodium channel with the protein 14-3-3 which in turn would be involved in the alpha-alpha interaction, we expressed two different BrS DN-mutants in HEK293 cells with and without difopein, a specific 14-3-3 inhibitor. The presence of difopein abolished the DN-effect of both mutants. The DN-effect was also abolished when we mutated the putative 14-3-3 binding site on SCN5A and expressed the DN-mutants either in HEK293 cells or in iCells©. Inhibition of 14-3-3 also impaired the biophysical coupling observed in presence of SCN5A gating deficient mutants that affect either activation or inactivation of not only the mutants but also of the wild-type channel. Conclusions: Our results suggest that binding of 14-3-3 to the cardiac sodium channel alpha-subunit is involved in the alpha-alpha interaction and biophysical coupling of the channel. This study not only shifts paradigms in regards to sodium channel assembly and structure, but also puts forward the idea that physical and biophysical uncoupling of cardiac sodium channels could be a new therapy target for cardiac arrhythmias caused by SCN5A mutations.

The role of dexamethasone in scorpion venom-induced deregulation of sodium and water transport in rat lungs.

BackgroundSevere scorpion envenomation can evolve to lung injury and, in some cases, death. The lung injury could be attributed to acute left ventricular failure and increased pulmonary vascular permeability secondary to the release of inflammatory mediators. In clinical practice, corticosteroids have been administered to reduce the early side effects of the anti-venom. We propose to study the effects of Tityus serrulatus venom and dexamethasone on pulmonary expression of sodium and water transporters, as well as on the inflammatory response.MethodsWistar rats were injected intraperitoneally with saline (control group), dexamethasone, and saline (2.0 mg/kg body weight—60 min before saline injection; dexamethasone + saline group), venom (T. serrulatus venom—3.8 mg/kg body weight), or dexamethasone and venom (2.0 mg/kg body weight—60 min before venom injection; dexamethasone + venom group). At 60 min after venom/saline injection, experiments were performed in ventilated and non-ventilated animals. We analyzed sodium transporters, water transporters, and Toll-like receptor 4 (TLR4) by Western blotting, macrophage infiltration by immunohistochemistry, and serum interleukin (IL) by cytokine assay.ResultsIn the lung tissue of non-ventilated envenomed animals, protein expression of the epithelial sodium channel alpha subunit (α-ENaC) and aquaporin 5 (AQP5) were markedly downregulated whereas that of the Na-K-2Cl cotransporter (NKCC1) and TLR4 was elevated although expression of the Na,K-ATPase alpha 1 subunit was unaffected. Dexamethasone protected protein expression of α-ENaC, NKCC1, and TLR4 but not that of AQP5. We found that IL-6, IL-10, and tumor necrosis factor alpha were elevated in the venom and dexamethasone + venom groups although CD68 expression in lung tissue was elevated only in the venom group. Among the ventilated animals, both envenomed groups presented hypotension at 50 min after injection, and the arterial oxygen tension/fraction of inspired oxygen ratio was lower at 60 min than at baseline.ConclusionsOur results suggest that T. serrulatus venom and dexamethasone both regulate sodium transport in the lung and that T serrulatus venom regulates sodium transport via the TLR4 pathway.

Familial SCN1A missense mutation over three generations, from febrile seizures to severe myoclonic epilepsy in infancy

Mutations of the sodium channel alpha subunit type 1 gene (SCN1A) gene, encoding the voltage gated sodium channel alpha-subunit, represent the most frequent genetic cause of severe myoclonic epilepsy in infancy (SMEI). So far over 250 SMEI related SCN1A mutations have been identified of which 95% are considered de novo. We report a familial SCN1A missense mutation over three generations with extremely variable phenotypes, from simple febrile seizures to SMEI. Severe myoclonic epilepsy in infancy (SMEI) or Dravet syndrome is an age-dependent epileptic en- cephalopathy with onset during the first year of life. Common manifestations of the disorder are often pro- longed hemiclonic or generalized tonic-clonic seizures, usually associated with fever, in previously healthy in- fants with normal psychomotor development. Inter- ictal electroencephalography (EEG) shows no sign of epileptic activity in the early course of the disease. The condition evolves with a variety of afebrile or fever- induced seizure types (myoclonic, atonic, absence and partial seizures) in the second year of life. Develop- mental stagnation occurs with many children showing ataxia and slowing in speech development; cognitive outcome is poor with a high risk of mental retarda-

Dravet syndrome: A case report with a new missense substitution as 1274 Tyr > Asp

Dravet syndrome is a severe form of epilepsy and also is called severe myoclonic epilepsy of infancy (SMEI). It appears during the first year of life with frequent febrile se izures, fever related seizures, which is rare beyond the age of 5 years. Children with SMEI typically experience poor development of language, motor skills, hyperactivity, and difficulty in m aking relationship. Thirty to eighty percent of patients with Dra vet syndrome, which is known as classical form of SMEI, suffer from defects in a gene involved in proper function of brain cells. The patient is a 3-years-old girl presenting with a sudden epileptic seizure. She had 2-year history of severe myoclonic epilepsy and developmental delay that was diagnosed as Dravet syndrome. A novel missense substitution in sodium channel alpha subunit type 1 was detected and the novelty of substitution confirm ed by molecular analysis in healthy family members as well as control group. As an early diagnosis, the clinical screening pro cedure used by pediatricians as well as a sodium channel alpha subunit type 1 mutation analysis could help to predict Dravet syndrome before 1 year of age, so the pediatricians could be able to manage clinical work-up properly.

A Common Polymorphism of the Human Cardiac Sodium Channel Alpha Subunit (SCN5A) Gene Is Associated with Sudden Cardiac Death in Chronic Ischemic Heart Disease.

Cardiac death remains one of the leading causes of mortality worldwide. Recent research has shed light on pathophysiological mechanisms underlying cardiac death, and several genetic variants in novel candidate genes have been identified as risk factors. However, the vast majority of studies performed so far investigated genetic associations with specific forms of cardiac death only (sudden, arrhythmogenic, ischemic etc.). The aim of the present investigation was to find a genetic marker that can be used as a general, powerful predictor of cardiac death risk. To this end, a case-control association study was performed on a heterogeneous cohort of cardiac death victims (n=360) and age-matched controls (n=300). Five single nucleotide polymorphisms (SNPs) from five candidate genes (beta2 adrenergic receptor, nitric oxide synthase 1 adaptor protein, ryanodine receptor 2, sodium channel type V alpha subunit and transforming growth factor-beta receptor 2) that had previously been shown to associate with certain forms of cardiac death were genotyped using sequence-specific real-time PCR probes. Logistic regression analysis revealed that the CC genotype of the rs11720524 polymorphism in the SCN5A gene encoding a subunit of the cardiac voltage-gated sodium channel occurred more frequently in the highly heterogeneous cardiac death cohort compared to the control population (p=0.019, odds ratio: 1.351). A detailed subgroup analysis uncovered that this effect was due to an association of this variant with cardiac death in chronic ischemic heart disease (p=0.012, odds ratio = 1.455). None of the other investigated polymorphisms showed association with cardiac death in this context. In conclusion, our results shed light on the role of this non-coding polymorphism in cardiac death in ischemic cardiomyopathy. Functional studies are needed to explore the pathophysiological background of this association.

The role of the SCN5A-encoded channelopathy in irritable bowel syndrome and other gastrointestinal disorders.

Gastrointestinal functional and motility disorders, like irritable bowel syndrome (IBS), have a high prevalence in the Western population and cause significant morbidity and loss of quality of life leading to considerable costs for health care. A decade ago, it has been demonstrated that interstitial cells of Cajal and intestinal smooth muscle cells, cells important for gastrointestinal motility, express the sodium channel alpha subunit Nav 1.5. In the heart, aberrant variants in this sodium channel, encoded by SCN5A, are linked to inherited arrhythmia syndromes, like the long-QT syndrome type 3 and Brugada syndrome. Mounting data show a possible contribution of SCN5A mutants to gastrointestinal functional and motility disorders. Two percent of IBS patients harbor SCN5A mutations with electrophysiological evidence of loss- and gain-of-function. In addition, gastrointestinal symptoms are more prevalent in cardiac SCN5A-mutation positive patients. This review firstly describes the Nav 1.5 channel and its physiological role in ventricular cardiomyocytes and gastrointestinal cells, then we focus on the involvement of mutant Nav 1.5 in gastrointestinal functional and motility disorders. Future research might uncover novel mutation-specific treatment strategies for SCN5A-encoded gastrointestinal channelopathies.

The incidence of SCN1A‐related Dravet syndrome in Denmark is 1:22,000: A population‐based study from 2004 to 2009

Dravet syndrome is a severe infantile-onset epileptic encephalopathy associated with mutations in the sodium channel alpha-1 subunit gene SCN1A. We aimed to describe the incidence of Dravet syndrome in the Danish population. Based on a 6-year birth cohort from 2004 to 2009, we propose an incidence of 1:22,000, which is higher than what has been established earlier. We identified 17 cases with SCN1A mutation-positive Dravet syndrome. Fifteen patients were found, by conventional Sanger sequencing. Two additional patients with clinical Dravet syndrome, but without a detectable SCN1A mutation by Sanger sequencing, were diagnosed with a SCN1A mutation after using a targeted next-generation sequencing gene panel.

A long isoform of the epithelial sodium channel alpha subunit forms a highly active channel

A long isoform of the human Epithelial Sodium Channel (ENaC) α subunit has been identified, but little data exist regarding the properties or regulation of channels formed by α728. The baseline whole cell conductance of oocytes expressing trimeric α728βγ channels was 898.1 ± 277.2 and 49.59 ± 13.2 µS in low and high sodium solutions, respectively, and was 11 and 2 fold higher than the conductances of α669βγ in same solutions. α728βγ channels were also 2 to 5 fold less sensitive to activation by the serine proteases subtilisin and trypsin than α669βγ in low and high Na+ conditions. The long isoform exhibited lower levels of full length and cleaved protein at the plasma membrane and a rightward shifted sensitivity to inhibition by increases of [Na+]i. Both channels displayed similar single channel conductances of 4 pS, and both were activated to a similar extent by reducing temperature, altogether indicating that activation of baseline conductance of α728βγ was likely mediated by enhanced channel activity or open probability. Expression of α728 in native kidneys was validated in human urinary exosomes. These data demonstrate that the long isoform of αENaC forms the structural basis of a channel with different activity and regulation, which may not be easily distinguishable in native tissue, but may underlie sodium hyperabsorption and salt sensitive differences in humans.

Single-Channel Analysis of the Molecular Pharmacology of the Long QT Syndrome Variant 3

The Long QT Syndrome (LQTS) is characterized by a prolongation of the QT interval on an ECG and occurrences of ventricular fibrillation, polymorphic ventricular tachycardia, and sudden cardiac death. In patients with LQTS variant 3 (LQT3), mutations in the cardiac sodium channel alpha subunit, Nav1.5, disrupt channel inactivation by multiple mechanisms and can cause a sustained depolarizing current (INaL) sufficient to prolong the ventricular action potential. LQT3 mutant sodium channels are therefore a reliable experimental model for the study of the function and pharmacology of dysfunctional sodium currents in a wide range of more common acquired disorders that are linked by disease-altered INaL, including ischemic heart disease and heart failure. While preferential pharmacological block of INaL by several Na+-channel blocking drugs has proven to be an important and useful clinical approach to manage LQT-3 arrhythmias, we still lack a fundamental understanding of the pharmacological determinants of this selectivity. We have previously identified a novel lethal LQT3 variant, F1473C, which displays slowed inactivation, altered channel availability, and a significant INaL. Here we report for the first time single channel recordings from F1473C channels and find that late reopening events during prolonged depolarizations underlie pathological INaL for this mutation. To further unravel the mechanism of action of of Ranolazine, a drug known to preferentially block INaL, we studied its effects on single F1473C channels. Ranolazine reduced the number of late reopening events in a manner consistent with block of whole cell currents. These experiments represent the first exploration of the block of INaL caused by late reopening, and present a framework for further studies of the mechanisms of drug block in these channels.

<i>In Silico</i> Modeling of Voltage-gated Sodium Channel Alpha Subunit to Understand Insecticide Binding Simulation in Mosquitoes

The Voltage Gated Sodium Channel (VGSC) is critical for binding of different insecticides and play key role in insecticide resistance. An important mechanism of resistance to DDT and pyrethroids is termed knockdown resistance (kdr), caused by mutations in IIS6 domain of sodium channels. To attain a better management strategy for insecticide resistance and screening of new insecticide molecules, it is important to understand the three-dimensional structure of insecticide-binding domain of VGSC and its molecular interaction with insecticides. We constructed a theoretical model of ion transport domain–II of VGSC from mosquitoes, Culex quinquefasciatus . The stereochemistry of the model shows 91.1% residues are in the most favored region. Docking studies with DDT and deltamethrin indicated that deltamethrin showed interaction with Thr 929 , Met 918 , Ile 936 , Cys 933 , Leu 925 , Glu 881 , Met 857 and Gly 866 and DDT showed interaction with Ile 936 , Thr 929 , Ser 878 , Phe 863 , Gln 864 , Trp 861 and Met 857 . We also predicted that mutation of Thr 929 should confer resistance to both DDT and deltamethrin.

Interaction of the Cardiac Sodium Channel Alpha-Subunits Leads to Coupled Gating Properties

Objective: The cardiac sodium channel has been linked to cardiac arrhythmias. We have shown the existence of dominant-negative mutations in Brugada Syndrome due to interactions between alpha-subunits. Here we investigated the stoichiometry of the interaction and whether the interaction leads to coupled gating properties.Methods: Single-molecule pull-down experiments and blue native gels have been performed to study the stoichiometry of the interaction, while FRET/TIRF experiments were performed to investigate the interaction at the cell surface. Biophysical properties were studied by patch-clamp analysis in the whole-cell configuration.Results: Biochemistry results support the dimerization of alpha-subunits. FRET/TIRF experiments showed interacting channels at the plasma membrane. Also, we investigated if the dimerization of the channel leads to biophysical consequences. To do so, we used different mutants leading to specific biophysical. R1860X and R1629Q mutants were used for inactivation and R878C for gating deficiency. When cells expressed WT and R1629Q mutant channels, inactivation properties behaved more closely to the WT contrarily to what would be expected of 2 channels working independently. In addition, when R1629Q was coepxressed with the gating deficient mutant R878C we showed a significant improvement of the R1629Q inactivation properties, even though R878C is not conducting. We then used a truncated channel R1860X and once again the coexpression with R878C significantly improved the inactivation defect, which was not the case with the expression of a C-terminus fragment alone. This, strongly suggest that the presence of the full length channel could rescue the inactivation defect of the delta-Cter channel.Conclusions: Our data indicate that the alpha-subunits of the cardiac sodium channel present coupled gating properties due to the formation of dimers.

Super-resolution imaging reveals that loss of the C-terminus of connexin43 limits microtubule plus-end capture and NaV1.5 localization at the intercalated disc.

It is well known that connexin43 (Cx43) forms gap junctions. We recently showed that Cx43 is also part of a protein-interacting network that regulates excitability. Cardiac-specific truncation of Cx43 C-terminus (mutant 'Cx43D378stop') led to lethal arrhythmias. Cx43D378stop localized to the intercalated disc (ID); cell-cell coupling was normal, but there was significant sodium current (INa) loss. We proposed that the microtubule plus-end is at the crux of the Cx43-INa relation. Yet, specific localization of relevant molecular players was prevented due to the resolution limit of fluorescence microscopy. Here, we use nanoscale imaging to establish: (i) the morphology of clusters formed by the microtubule plus-end tracking protein 'end-binding 1' (EB1), (ii) their position, and that of sodium channel alpha-subunit NaV1.5, relative to N-cadherin-rich sites, and (iii) the role of Cx43 C-terminus on the above-mentioned parameters and on the location-specific function of INa. Super-resolution fluorescence localization microscopy in murine adult cardiomyocytes revealed EB1 and NaV1.5 as distinct clusters preferentially localized to N-cadherin-rich sites. Extent of co-localization decreased in Cx43D378stop cells. Macropatch and scanning patch clamp showed reduced INa exclusively at cell end, without changes in unitary conductance. Experiments in Cx43-modified HL1 cells confirmed the relation between Cx43, INa, and microtubules. NaV1.5 and EB1 localization at the cell end is Cx43-dependent. Cx43 is part of a molecular complex that determines capture of the microtubule plus-end at the ID, facilitating cargo delivery. These observations link excitability and electrical coupling through a common molecular mechanism.

COE loss-of-function analysis reveals a genetic program underlying maintenance and regeneration of the nervous system in planarians.

Members of the COE family of transcription factors are required for central nervous system (CNS) development. However, the function of COE in the post-embryonic CNS remains largely unknown. An excellent model for investigating gene function in the adult CNS is the freshwater planarian. This animal is capable of regenerating neurons from an adult pluripotent stem cell population and regaining normal function. We previously showed that planarian coe is expressed in differentiating and mature neurons and that its function is required for proper CNS regeneration. Here, we show that coe is essential to maintain nervous system architecture and patterning in intact (uninjured) planarians. We took advantage of the robust phenotype in intact animals to investigate the genetic programs coe regulates in the CNS. We compared the transcriptional profiles of control and coe RNAi planarians using RNA sequencing and identified approximately 900 differentially expressed genes in coe knockdown animals, including 397 downregulated genes that were enriched for nervous system functional annotations. Next, we validated a subset of the downregulated transcripts by analyzing their expression in coe-deficient planarians and testing if the mRNAs could be detected in coe+ cells. These experiments revealed novel candidate targets of coe in the CNS such as ion channel, neuropeptide, and neurotransmitter genes. Finally, to determine if loss of any of the validated transcripts underscores the coe knockdown phenotype, we knocked down their expression by RNAi and uncovered a set of coe-regulated genes implicated in CNS regeneration and patterning, including orthologs of sodium channel alpha-subunit and pou4. Our study broadens the knowledge of gene expression programs regulated by COE that are required for maintenance of neural subtypes and nervous system architecture in adult animals.

Increased cystic fibrosis transmembrane conductance regulators expression and decreased epithelial sodium channel alpha subunits expression in early abortion: findings from a mouse model and clinical cases of abortion.

The status of the maternal endometrium is vital in regulating humoral homeostasis and for ensuring embryo implantation. Cystic fibrosis transmembrane conductance regulators (CFTR) and epithelial sodium channel alpha subunits (ENaC-α) play an important role in female reproduction by maintaining humoral and cell homeostasis. However, it is not clear whether the expression levels of CFTR and ENaC-α in the decidual component during early pregnancy are related with early miscarriage. CBA×DBA/2 mouse mating has been widely accepted as a classical model of early miscarriage. The abortion rate associated with this mating was 33.33% in our study. The decidua of abortion-prone CBA female mice (DBA/2 mated) had higher CFTR mRNA and protein expression and lower ENaC-α mRNA and protein expression, compared to normal pregnant CBA mice (BLAB/C mated). Furthermore, increased CFTR expression and decreased ENaC-α expression were observed in the uterine tissue from women with early miscarriage, as compared to those with successful pregnancy. In conclusion, increased CFTR expression and decreased ENaC-α expression in the decidua of early abortion may relate with failure of early pregnancy.

Confirming an expanded spectrum of SCN2A mutations: a case series

Mutations in sodium channel genes are highly associated with epilepsy. Mutation of SCN1A, the gene encoding the voltage gated sodium channel (VGSC) alpha subunit type 1 (Nav1.1), causes Dravet syndrome spectrum disorders. Mutations in SCN2A have been identified in patients with benign familial neonatal-infantile epilepsy (BFNIE), generalised epilepsy with febrile seizures plus (GEFS+), and a small number of reported cases of other infantile-onset severe intractable epilepsy. Here, we report three patients with infantile-onset severe intractable epilepsy found to have de novo mutations in SCN2A. While a causal role for these mutations cannot be directly established, these findings contribute to growing evidence that mutation of SCN2A is associated with a range of epilepsy phenotypes including severe infantile-onset epilepsy.

Long‐term course of Dravet syndrome: A study from an epilepsy center in Japan

This study attempted to clarify the long-term course of Dravet syndrome (DS). Sixty-four patients diagnosed with DS (44 with typical DS, and 20 with atypical DS) were studied. The long-term outcomes of clinical seizures, electroencephalographic findings, neuropsychological findings, and social situation were analyzed. The follow-up period ranged from 11 to 34years 5months (median 24years). At the last visit, the ages ranged from 19years to 45years (median 30years). Fifty-nine patients continued to have generalized tonic-clonic seizures (GTCS). Status epilepticus and unilateral seizures were not observed and myoclonic seizures, atypical absence seizures, and photosensitive seizures were resolved in most patients. The frequency of complex partial seizures was equally low, with five patients at presentation and six patients at the last visit, respectively. Five patients achieved seizure remission (seizure-free for 1year or longer). Only 1 of 44 patients with typical DS had seizure remission, whereas 4 of 20 patients with atypical DS remitted, with a statistically significant difference between the two phenotypes (p=0.03). Intellectual disability was found in all patients; especially, severe intellectual disability was prevalent. Patients with atypical DS tended to have milder intellectual disability compared to those with typical DS (p=0.0283). Occipital alpha rhythm in the basic activity was associated with milder intellectual disability (p=0.0085). The freedom from seizures correlated with appearance of occipital alpha rhythms (p=0.0008) and disappearance of epileptic discharges (p=0.0004). Two patients with GTCS died. Mutations of the neuronal voltage-gated sodium channel alpha subunit type 1 gene were detected at a high frequency (33 of 36 patients examined). Seizure remission was found only in the missense mutation group. The long-term seizure and intellectual outcomes are extremely poor in patients with typical DS compared to those with atypical DS. Epilepsy phenotype may influence long-term course of DS.

Cardiac Sodium Channel Display Coupled Gating

Objective: Mutations in SCN5A, the gene encoding the cardiac sodium channel, have been linked to many inherited cardiac arrhythmias. We have shown the existence of dominant-negative mutations in Brugada Syndrome due to interactions between alpha-subunits. Here we investigated whether cardiac sodium channel alpha-subunits also display coupled gating in addition to interacting. Methods: Biophysical properties were studied by patch-clamp analysis in the whole-cell configuration. Results: We used a non-trafficking mutant which can be rescued with mexilitine, unveiling a +15 mV shift in activation compared to WT. When this non-trafficking mutant was co-expressed with WT, we still saw a shift in activation compared to WT alone, even though the mutant is not conducting. Therefore these results demonstrate that the presence of the mutant, affects the activation of the WT suggesting a gating cooperation between the 2 channels. Then we wanted to address whether the inactivation gating process was also synergic between two sodium channel subunits. We used a channel where the C-terminus was deleted and where inactivation was affected. Expression of this delta-Cter alone showed altered inactivation kinetics. Surprisingly, when co-transfected with the trafficking-competent but gating-deficient mutant channel R878C, the inactivation properties of the mutant were partially rescued. Altogether these data suggest that the presence of the full C-terminal region provided by the nonfunctional channel R878C could rescue the inactivation defect of the delta-Cter channel. Conclusions: Mutations impairing either activation or inactivation of one channel can affect the gating properties of the other WT alpha-subunit demonstrating coupled gating properties between sodium channel alpha-subunits.

In silico docking reveals possible Riluzole binding sites on Nav1.6 sodium channel: implications for drug design strategy on Amyotrophic Lateral Sclerosis

Event Abstract Back to Event In silico docking reveals possible Riluzole binding sites on Nav1.6 sodium channel: implications for drug design strategy on Amyotrophic Lateral Sclerosis Omar Sierra1*, Janneth González1 and George Barreto1 1 Pontificia Universidad Javeriana, Colombia Amyotrophic Lateral Sclerosis (ALS) is a progressive neuromuscular disorder involving primarily motor neurons (Hoffman 2008). Glutamate excitotoxicity has been suggested to contribute to this progressive loss of motor neurons due to astrocytes reduced ability to uptake this neurotransmitter (Van Den Bosch 2006). Previous reports revealed that the Na+ channel blockade may increase motor neurons survival against excitotoxic death by targeting the Sodium channel protein Nav1.6 (Hebert et al. 1994). Riluzole interferes with glutamate-mediated transmission, thereby reducing excitotoxicity (Tavakoli 2002). These effects may be partly due to inactivation of voltage-dependent sodium channels Nav1.6 (Ajroud-Driss et al. 2007), suggesting an indirect effect of this drug on glutamate transporters. However many concerns are still unresolved due to experimental caveats, the lack of significant theoretical guidance (Fu et al. 2002) and experimental data on the structure of Riluzole-VGSc complexes. In this study, we have integrated a docking analysis and homology modeling to understand the association of Riluzole with the alpha subunit of voltage-gated sodium channel Nav 1.6. First, we have constructed the three-dimensional structure model for the voltage-gated sodium channel subunit alpha Nav1.6 via homology modeling. Our results demonstrate that Riluzole interacts with the Nav1.6 channel, more specifically in the key residues TYR 1787, LEU 1843 and GLN 1799, suggesting possible cellular implications driven by these amino acids on Riluzole-Nav1.6 interaction, which may serve as an important output for a more specific and experimental drug design therapy against ALS References. Ajroud-Driss S, et al. 2007. Riluzole metabolism and CYP1A1/2 polymorphisms in patients with ALS. Amyotroph Lateral Scler 8: 305-309. Hebert T, Drapeau P, Pradier L, Dunn R. 1994. Block of the rat brain IIA sodium channel alpha subunit by the neuroprotective drug riluzole. Molecular pharmacology 45: 1055-1060. Hoffman JJ. 2008. Toward a better understanding of amyotrophic lateral sclerosis. Home Healthc Nurse 26: 337-342; quiz 343-334. Tavakoli M. 2002. Disease progression in amyotrophic lateral sclerosis. Identifying the cost-utility of riluzole by disease stage. The european journal health economycs 3: 156-165. Van Den Bosch L, Van Damme, P., Bogaert, E., & Robberecht, W. . 2006.amyotrophic lateral sclerosis. Biochimica Et Biophysica Acta - Mol ecular Basis of Disease: 1762(1711–1712) 1068-1082 Keywords: computational neuroscience, Amyotrophic lateral sclerosis (ALS), glutamate excitotoxicity, 3D structure, nav1.6 Conference: 5th INCF Congress of Neuroinformatics, Munich, Germany, 10 Sep - 12 Sep, 2012. Presentation Type: Poster Topic: Neuroinformatics Citation: Sierra O, González J and Barreto G (2014). In silico docking reveals possible Riluzole binding sites on Nav1.6 sodium channel: implications for drug design strategy on Amyotrophic Lateral Sclerosis. Front. Neuroinform. Conference Abstract: 5th INCF Congress of Neuroinformatics. doi: 10.3389/conf.fninf.2014.08.00078 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 21 Mar 2013; Published Online: 27 Feb 2014. * Correspondence: Dr. Omar Sierra, Pontificia Universidad Javeriana, BOGOTA, Colombia, osierra@javeriana.edu.co Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Omar Sierra Janneth González George Barreto Google Omar Sierra Janneth González George Barreto Google Scholar Omar Sierra Janneth González George Barreto PubMed Omar Sierra Janneth González George Barreto Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.