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Analysis of paralytic shellfish poisoning toxin congeners by a sodium channel receptor binding assay

Usup G, Leaw CP, Cheah MY, Ahmad A, Ng BK

Toxicon, 2004 Jul;44(1):37-43.
PMID: 15225560

This study was carried out to characterize the detection and quantitation of several paralytic shellfish poisoning (PSP) toxin congeners using a receptor binding assay (RBA). This involved competitive binding of the toxin congeners against tritium-labeled STX for receptor sites on rat brain sodium channels. Competitive binding curves were described by a four-parameter logistic equation. Half-saturation values (EC(50)) ranged from 4.38 nM for STX to 142 nM for GTX5. Receptor binding affinity was in the order STX>GTX1/4>neoSTX>GTX2/3>dcSTX>GTX5, and this was similar to the order of mouse toxicity of these congeners. Predicted toxin concentrations from observed STXeq values and EC(50) ratios relative to STX were within 20% or better of the actual concentrations used in the assay. In contrast predicted toxin concentrations using mouse toxicity ratios relative to STX did not provide a good match to actual concentrations, except for GTX1/4. This study has shown that the rat brain sodium channel RBA will provide a reliable integration of total toxicity of various PSP toxin congeners present in a sample.

Matched MeSH terms: Sodium Channels/metabolism*
Case-control association study of polymorphisms in the voltage-gated sodium channel genes SCN1A, SCN2A, SCN3A, SCN1B, and SCN2B and epilepsy

Baum L, Haerian BS, Ng HK, Wong VC, Ng PW, Lui CH, et al.

Hum Genet, 2014 May;133(5):651-9.
PMID: 24337656 DOI: 10.1007/s00439-013-1405-1

High-frequency action potentials are mediated by voltage-gated sodium channels, composed of one large α subunit and two small β subunits, encoded mainly by SCN1A, SCN2A, SCN3A, SCN1B, and SCN2B genes in the brain. These play a key role in epilepsy, with the most commonly mutated gene in epilepsy being SCN1A. We examined whether polymorphisms in the above genes affect epilepsy risk in 1,529 epilepsy patients and 1,935 controls from four ethnicities or locations: Malay, Indian, and Chinese, all from Malaysia, and Chinese from Hong Kong. Of patients, 19 % were idiopathic, 42 % symptomatic, and 40 % cryptogenic. We genotyped 43 polymorphisms: 27 in Hong Kong, 28 in Malaysia, and 12 in both locations. The strongest association with epilepsy was rs3812718, or SCN1A IVS5N+5G>A: odds ratio (OR) = 0.85 for allele G (p = 0.0009) and 0.73 for genotype GG versus AA (p = 0.003). The OR was between 0.76 and 0.87 for all ethnicities. Meta-analysis confirmed the association (OR = 0.81 and p = 0.002 for G, and OR = 0.67 and p = 0.007 for GG versus AA), which appeared particularly strong for Indians and for febrile seizures. Allele G affects splicing and speeds recovery from inactivation. Since SCN1A is preferentially expressed in inhibitory neurons, G may decrease epilepsy risk. SCN1A rs10188577 displayed OR = 1.20 for allele C (p = 0.003); SCN2A rs12467383 had OR = 1.16 for allele A (p = 0.01), and displayed linkage disequilibrium with rs2082366 (r (2) = 0.67), whose genotypes tended toward association with SCN2A brain expression (p = 0.10). SCN1A rs2298771 was associated in Indians (OR = 0.56, p = 0.005) and SCN2B rs602594 with idiopathic epilepsy (OR = 0.62, p = 0.002). Therefore, sodium channel polymorphisms are associated with epilepsy.

Matched MeSH terms: Sodium Channels/genetics*; Sodium Channels/physiology
Changes in plasma aldosterone and electrolytes levels, kidney epithelial sodium channel (ENaC) and blood pressure in normotensive WKY and hypertensive SHR rats following gonadectomy and chronic testosterone treatment

Loh SY, Giribabu N, Salleh N

Steroids, 2017 Dec;128:128-135.
PMID: 28954214 DOI: 10.1016/j.steroids.2017.09.008

We hypothesized that testosterone-induced increase in blood pressure involve changes in aldosterone levels and expression of epithelial sodium channel (ENaC) in the kidneys.
METHODS: Ovariectomized female normotensive Wistar Kyoto (WKY) and Spontaneous hypertensive (SHR) rats were given six weeks treatment with testosterone via subcutaneous silastic implant. The rats were anesthetized and mean arterial pressure (MAP) was measured via direct cannulation of the carotid artery. Animals were sacrificed and kidneys were removed and subjected for α, β and γ-ENaC protein and mRNA expression analyses by Western blotting and Real-time polymerase chain reaction (qPCR), respectively. Distributions of α, β and γ-ENaC proteins in kidneys were observed by immunofluorescence. Plasma testosterone, aldosterone, electrolytes, osmolality, urea and creatinine levels were determined by biochemical assays. Analysis were also performed in non-testosterone treated orchidectomized and sham-operated male WKY and SHR rats.
RESULTS: Treatment of ovariectomized female WKY and SHR rats with testosterone causes increased in MAP but decreased in plasma aldosterone, sodium (Na+), osmolality and expression and distribution of α, β and γ-ENaC subunits in the kidneys. Orchidectomy decreased the MAP but increased plasma aldosterone, Na+, osmolality and α, β and γ-ENaC expression and distribution in the kidneys of male WKY and SHR rats.
CONCLUSIONS: Decreased in plasma aldosterone, Na+ and ENaC levels in kidneys under testosterone influence indicated that testosterone-induced increased in MAP were not due to increased plasma aldosterone and ENaC levels in kidneys, and thus the testosterone effect on MAP likely involve other mechanisms.

Matched MeSH terms: Epithelial Sodium Channels/genetics*
Fulltext Combinatorial effects of quercetin and sex-steroids on fluid and electrolytes' (Na+, Cl-, HCO3-) secretory mechanisms in the uterus of ovariectomised female Sprague-Dawley rats

Shahzad H, Giribabu N, Karim K, Kassim NM, Muniandy S, Salleh N

PLoS One, 2017;12(3):e0172765.
PMID: 28253299 DOI: 10.1371/journal.pone.0172765

Dysregulation of uterine fluid environment could impair successful reproduction and this could be due to the effect of environmental estrogens. Therefore, in this study, effect of quercetin, an environmental estrogen on uterine fluid and electrolytes concentrations were investigated under sex-steroid influence. Ovariectomised adult female Sprague-Dawley rats were given 10, 50 or 100mg/kg/day quercetin subcutaneously with 17-β estradiol (E) for seven days or three days E, then three days E plus progesterone (P) (E+P) treatment. Uterine fluid secretion rate, Na+, Cl- and HCO3- concentrations were determined by in-vivo perfusion. Following sacrifice, uteri were harvested and levels of the proteins of interest were identified by Western blotting and Realtime PCR. Distribution of these proteins in the uterus was observed by immunofluorescence. Levels of uterine cAMP were measured by enzyme-linked immunoassay (EIA). Administration of quercetin at increasing doses increased uterine fluid secretion rate, Na+, Cl- and HCO3- concentrations, but to the levels lesser than that of E. In concordant, levels of CFTR, SLC4A4, ENaC (α, β and γ), Na+/K+-ATPase, GPα/β, AC and cAMP in the uterus increased following increased in the doses of quercetin. Co-administration of quercetin with E caused uterine fluid secretion rate, Na+, Cl- and HCO3- concentrations to decrease. In concordant, uterine CFTR, SLC26A6, SLC4A4, ENaC (α, β and γ), Na+/K+-ATPase, GPα/β, AC and cAMP decreased. Greatest effects were observed following co-administration of 10mg/kg/day quercetin with E. Co-administration of quercetin with E+P caused uterine fluid Na+ and HCO3- concentrations to increase but no changes in fluid secretion rate and Cl- concentration were observed. Co-administration of high dose quercetin (100 mg/kg/day) with E+P caused uterine CFTR, SLC26A6, AC, GPα/β and ENaC (α, β and γ) to increase. Quercetin-induced changes in the uterine fluid secretion rate and electrolytes concentrations could potentially affect the uterine reproductive functions under female sex-steroid influence.

Matched MeSH terms: Epithelial Sodium Channels/genetics; Epithelial Sodium Channels/metabolism
Effect of age, weight, race and sex on blood pressure and erythrocyte sodium pump characteristics

Adeeb N, Ton SH, Muslim N

Clin Exp Hypertens A, 1990;12(6):1115-34.
PMID: 2173984

In order to examine whether erythrocyte membrane handling of sodium is influenced by factors other than hypertension, measurements of red cell sodium transport were studied in one hundred normotensive volunteers. Erythrocyte sodium content was found to increase with increasing age, body weight and mean arterial pressure (MAP). It is also significantly correlated with age, body weight and MAP. Total sodium efflux was found to be reduced and negatively correlated with age and body weight. A reduction in ouabain-sensitive sodium efflux was also observed with increasing age and body weight. In males, the rate of ouabain-sensitive sodium efflux is higher than in females. Race was found to have no effect on erythrocyte electrolyte content and cationic flux rates of subjects. These data suggest that when studies in hypertension are going to be carried out, control subjects carefully matched for age, body weight and sex should be used if confounding results are not to be obtained.

Matched MeSH terms: Sodium Channels/metabolism*
Effects of a high-salt diet on MAP and expression levels of renal ENaCs and aquaporins in SHR

Ramachandran CD, Gholami K, Lam SK, Hoe SZ

Exp Biol Med (Maywood), 2023 Oct;248(20):1768-1779.
PMID: 37828834 DOI: 10.1177/15353702231198085

An increase in blood pressure by a high-salt (HS) diet may change the expression levels of renal epithelial sodium channels (ENaCs) and aquaporins (AQPs). Spontaneously hypertensive rats (SHRs) and Wistar Kyoto (WKY) rats were exposed to HS and regular-salt (RS) diets for 6 weeks. Mean arterial pressure (MAP) and plasma atrial natriuretic peptide (ANP), angiotensin II (Ang II), aldosterone, and arginine vasopressin (AVP) levels were determined. Expression of mRNA levels of ENaCs and AQPs were quantified by real-time PCR. The MAP was higher in SHRs on the HS diet. Plasma Ang II and aldosterone levels were low while plasma ANP level was high in both strains of rats. Renal expression of mRNA levels of α-, β-, and γ-ENaCs was lowered in SHRs on the HS diet. Meanwhile, renal AQP1, AQP2, and AQP7 mRNA expression levels were lowered in both strains of rats on the HS diet. Suppression of mRNA expression levels of ENaC and AQP subunits suggests that the high-salt-induced increase in the MAP of SHR may not be solely due to renal sodium and water retention.

Matched MeSH terms: Epithelial Sodium Channels/genetics; Epithelial Sodium Channels/metabolism
Fulltext Enzymatic and molecular characterization of insecticide resistance mechanisms in field populations of Aedes aegypti from Selangor, Malaysia

Leong CS, Vythilingam I, Liew JW, Wong ML, Wan-Yusoff WS, Lau YL

Parasit Vectors, 2019 May 16;12(1):236.
PMID: 31097010 DOI: 10.1186/s13071-019-3472-1

BACKGROUND: Dengue is a serious public health problem worldwide, including in Selangor, Malaysia. Being an important vector of dengue virus, Aedes aegypti are subjected to control measures which rely heavily on the usage of insecticides. Evidently, insecticide resistance in Ae. aegypti, which arise from several different point mutations within the voltage-gated sodium channel genes, has been documented in many countries. Thus, this robust study was conducted in all nine districts of Selangor to understand the mechanisms of resistance to various insecticides in Ae. aegypti. Mosquitoes were collected from dengue epidemic and non-dengue outbreak areas in Selangor.
METHODS: Using the Center for Disease Control and Prevention (CDC) bottle assays, the insecticide resistance status of nine different Ae. aegypti strains from Selangor was accessed. Synergism tests and biochemical assays were conducted to further understand the metabolic mechanisms of insecticide resistance. Polymerase chain reaction (PCR) amplification and sequencing of the IIP-IIS6 as well as IIIS4-IIIS6 regions of the sodium channel gene were performed to enable comparisons between susceptible and resistant mosquito strains. Additionally, genomic DNA was used for allele-specific PCR (AS-PCR) genotyping of the gene to detect the presence of F1534C, V1016G and S989P mutations.
RESULTS: Adult female Ae. aegypti from various locations were susceptible to malathion and propoxur. However, they exhibited different levels of resistance against dichlorodiphenyltrichloroethane (DDT) and pyrethroids. The results of synergism tests and biochemical assays indicated that the mixed functions of oxidases and glutathione S-transferases contributed to the DDT and pyrethroid resistance observed in the present study. Besides detecting three single kdr mutations, namely F1534C, V1016G and S989P, co-occurrence of homozygous V1016G/S989P (double allele) and F1534C/V1016G/S989P (triple allele) mutations were also found in Ae. aegypti. As per the results, the three kdr mutations had positive correlations with the expressions of resistance to DDT and pyrethroids.
CONCLUSIONS: In view of the above outcomes, it is important to seek new tools for vector management instead of merely relying on insecticides. If the latter must be used, regular monitoring of insecticide resistance should also be carried out at all dengue epidemic areas. Since the eggs of Ae. aegypti can be easily transferred from one location to another, it is probable that insecticide-resistant Ae. aegypti can be found at non-dengue outbreak sites as well.

Matched MeSH terms: Sodium Channels/genetics
Fulltext Epac-induced ryanodine receptor type 2 activation inhibits sodium currents in atrial and ventricular murine cardiomyocytes

Valli H, Ahmad S, Sriharan S, Dean LD, Grace AA, Jeevaratnam K, et al.

Clin Exp Pharmacol Physiol, 2018 03;45(3):278-292.
PMID: 29027245 DOI: 10.1111/1440-1681.12870

Acute RyR2 activation by exchange protein directly activated by cAMP (Epac) reversibly perturbs myocyte Ca2+ homeostasis, slows myocardial action potential conduction, and exerts pro-arrhythmic effects. Loose patch-clamp studies, preserving in vivo extracellular and intracellular conditions, investigated Na+ current in intact cardiomyocytes in murine atrial and ventricular preparations following Epac activation. Depolarising steps to varying test voltages activated typical voltage-dependent Na+ currents. Plots of peak current against depolarisation from resting potential gave pretreatment maximum atrial and ventricular currents of -20.23 ± 1.48 (17) and -29.8 ± 2.4 (10) pA/μm2 (mean ± SEM [n]). Challenge by 8-CPT (1 μmol/L) reduced these currents to -11.21 ± 0.91 (12) (P .05). Assessment of the inactivation that followed by applying subsequent steps to a fixed voltage 100 mV positive to resting potential gave concordant results. Half-maximal inactivation voltages and steepness factors, and time constants for Na+ current recovery from inactivation in double-pulse experiments, were similar through all the pharmacological conditions. Intracellular sharp microelectrode membrane potential recordings in intact Langendorff-perfused preparations demonstrated concordant variations in maximum rates of atrial and ventricular action potential upstroke, (dV/dt)max . We thus demonstrate an acute, reversible, Na+ channel inhibition offering a possible mechanism for previously reported pro-arrhythmic slowing of AP propagation following modifications of Ca2+ homeostasis, complementing earlier findings from chronic alterations in Ca2+ homeostasis in genetically-modified RyR2-P2328S hearts.

Matched MeSH terms: Sodium Channels
Estrogen, progesterone, and genistein differentially regulate levels of expression of α-, β-, and γ-epithelial sodium channel (ENaC) and α-sodium potassium pump (Na⁺/K⁺-ATPase) in the uteri of sex steroid-deficient rats

Chinigarzadeh A, Muniandy S, Salleh N

Theriogenology, 2015 Oct 1;84(6):911-26.
PMID: 26154487 DOI: 10.1016/j.theriogenology.2015.05.029

Estrogen, progesterone, and genistein could induce changes in uterine fluid volume and Na(+) concentration. Progesterone upregulates expression of epithelial sodium channel (ENaC) and Na(+)/K(+)-ATPase which contributed toward these changes. However, effects of estrogen and genistein were unknown. This study therefore investigated changes in expression of these proteins in the uterus under estrogen, progesterone, and genistein influences to further understand mechanisms underlying sex steroids and phytoestrogen effects on uterine fluid Na(+) regulation. In this study, uteri of ovariectomized female rats receiving 7-day treatment with genistein (25, 50, and 100 mg/kg/day), estrogen (0.8 × 10(-4) mg/kg/day), or progesterone (4 mg/kg/day) were harvested, and expression levels of α-, β-, and γ-ENaC proteins and messenger RNAs (mRNAs) and α-Na(+)/K(+)-ATPase protein were determined by Western blotting (proteins) and real-time polymerase chain reaction (mRNA). Meanwhile, distribution of α-, β-, and γ-ENaC and α-Na(+)/K(+)-ATPase proteins in the uterus was identified by immunohistochemistry. Our findings indicated that expression of α-, β-, and γ-ENaC proteins and mRNAs and α-Na(+)/K(+)-ATPase protein were enhanced under progesterone influence. Lower expressions were noted under estrogen and genistein influences compared to progesterone. Under estrogen, progesterone, and genistein influences, α- and β-ENaC were distributed at apical membrane and γ-ENaC was distributed at apical and basolateral membranes of uterine luminal epithelia. Under progesterone influence, α-Na(+)/K(+)-ATPase was highly expressed at basolateral membrane. In conclusion, high expression of α-, β-, and γ-ENaC and α-Na(+)/K(+)-ATPase under progesterone influence would contribute toward increased uterine fluid Na(+) reabsorption, whereas lesser expression of these proteins under estrogen and genistein influences would contribute toward lower reabsorption of uterine fluid Na(+).

Matched MeSH terms: Epithelial Sodium Channels
First molecular genotyping of voltage gated sodium channel alleles in Culex quinquefasciatus populations in Malaysia

Low VL, Chen CD, Lim PE, Lee HL, Tan TK, Lim YA, et al.

Pestic Biochem Physiol, 2013 Sep;107(1):127-31.
PMID: 25149246 DOI: 10.1016/j.pestbp.2013.06.004

A nationwide investigation was performed to detect the presence of 1014 mutation(s) in voltage gated sodium channel (kdr) gene of Culex quinquefasciatus from 14 residential areas across 13 states and a federal territory in Malaysia. Molecular genotyping of kdr mutation was performed via a modified three tubes allele-specific-polymerase chain reaction (AS-PCR) and direct sequencing of kdr gene. Based on the results of AS-PCR, homozygous susceptible (SS) genotype was found in nine out of 14 populations with 38 individuals from a total sample size of 140. Heterozygous (RS) genotype was most predominant (99 individuals) and distributed across all study sites. Homozygous resistance (RR) genotype was detected in Perak (one individual) and Selangor (two individuals). The resistance kdr allele frequencies ranged from 0.1 to 0.55, with the highest being detected in Cx. quinquefasciatus population from Selangor. This study has documented the first field-evolved instance of 1014F mutation in Malaysian mosquitoes and the findings of this study could be utilized in the implementation of strategic measures in vector control programs in Malaysia.

Matched MeSH terms: Voltage-Gated Sodium Channels/genetics*
Fulltext Generalized epilepsy with febrile seizure plus (GEFS+) spectrum: Novel de novo mutation of SCN1A detected in a Malaysian patient

Tan EH, Yusoff AA, Abdullah JM, Razak SA

J Pediatr Neurosci, 2012 May;7(2):123-5.
PMID: 23248692 DOI: 10.4103/1817-1745.102575

In this report, we describe a 15-year-old Malaysian male patient with a de novo SCN1A mutation who experienced prolonged febrile seizures after his first seizure at 6 months of age. This boy had generalized tonic clonic seizure (GTCS) which occurred with and without fever. Sequencing analysis of voltage-gated sodium channel a1-subunit gene, SCN1A, confirmed a homozygous A to G change at nucleotide 5197 (c.5197A > G) in exon 26 resulting in amino acid substitution of asparagines to aspartate at codon 1733 of sodium channel. The mutation identified in this patient is located in the pore-forming loop of SCN1A and this case report suggests missense mutation in pore-forming loop causes generalized epilepsy with febrile seizure plus (GEFS+) with clinically more severe neurologic phenotype including intellectual disabilities (mental retardation and autism features) and neuropsychiatric disease (anxiety disorder).

Matched MeSH terms: Sodium Channels
Identification of putative kdr mutations in the tropical bed bug, Cimex hemipterus (Hemiptera: Cimicidae)

Dang K, Toi CS, Lilly DG, Lee CY, Naylor R, Tawatsin A, et al.

Pest Manag Sci, 2015 Jul;71(7):1015-20.
PMID: 25132449 DOI: 10.1002/ps.3880

Bed bugs [both Cimex hemipterus (F.) and Cimex lectularius L.] are highly resistant to pyrethroids worldwide. An important resistance mechanism known as 'knockdown resistance' (kdr) is caused by genetic point mutations on the voltage-gated sodium channel (VGSC) gene. Previous studies have identified two point mutations (V419L and L925I) on the VGSC gene in C. lectularius that are responsible for kdr-type resistance. However, the kdr mutations in C. hemipterus have not been investigated.

Matched MeSH terms: Voltage-Gated Sodium Channels/genetics
Fulltext Lack of meaningful genotype-phenotype association in SCN1A-related infantile-onset epileptic encephalopathies

Siti Aishah Abdul Wahab, Yusnita Yakob, Khoo,Teik-Beng, Sangita Dharshini Terumalay, Vigneswari Ganesan, Teh,Chee-Ming, et al.

Neurology Asia, 2017;22(2):99-111.
MyJurnal

Background & Objective: SCN1A gene which encodes for sodium channel alpha 1 subunit has been
found to be the most common mutated gene in patients with epilepsy. This study aims to characterize the
SCN1A mutations as well as to describe genotype and phenotype association in children with SCN1Arelated
infantile-onset epileptic encephalopathies in Malaysia.

Methods: Children with infantile-onset
epileptic encephalopathy mostly suspected to have Dravet syndrome who had mutational analysis for
SCN1A gene from hospitals all over Malaysia were included in the study. Their epilepsy syndrome
diagnosis was classified into severe myoclonic epilepsy in infancy and its variants. Polymerase chain
reaction and bidirectional sequencing were used to identify SCN1A mutations.

Results: A total of 38
children with heterozygous mutations were analysed, 22 (57.9%) of which were novel mutations.
Truncated mutations were the most common mutation type (19, 50%). Other mutation types were
missense mutations (14, 36.8%), splice site mutations (4, 10.5%) and in-frame deletion (1, 2.6%). The
mean age of seizure onset was 4.7 months. Seizure following vaccination was observed in 26.3% of
the children. All of them had drug resistant epilepsy. There was no significant association between
the type of mutation with the syndromic diagnosis, age of seizure onset, tendency of the seizures to
cluster or having status epilepticus, mean age when developmental delay was observed and response
to various antiepileptic drugs.

Conclusion: This study expands the spectrum of SCN1A mutations and proves the importance of
SCN1A gene testing in diagnosing infantile-onset epileptic encephalopathies patients. Although, our
study does not support any clinically meaningful genotype-phenotype association for SCN1A-related
infantile-onset epileptic encephalopathies, the clinical characteristics of our cohort are similar to those
that have been described in previous studies.

Matched MeSH terms: Sodium Channels
Fulltext Low efficacy of delthamethrin-treated net against Singapore Aedes aegypti is associated with kdr-type resistance

Pang SC, Chiang LP, Tan CH, Vythilingam I, Lam-Phua SG, Ng LC

Trop Biomed, 2015 Mar;32(1):140-50.
PMID: 25801264 MyJurnal

There has been a worldwide surge in the number and severity of dengue in the past decades. In Singapore, relentless vector control efforts have been put in to control the disease since the 1960's. Space spraying, fogging, chemical treatment and source reduction are some commonly used methodologies for controlling its vectors, particularly Aedes aegypti. Here, as we explored the use of a commercially available delthamethrin-treated net as an alternative strategy and the efficacy of the treated net was found to be limited. Through bioassays and molecular studies, the failure of the treated net to render high mortality rate was found to be associated with the knockdown resistance (kdr) mutation. This is the first report of kdr- mutations in Singapore's Ae. aegypti. At least one point mutation, either homozygous or heterozygous, at amino acid residue V1016G of DIIS6 or F1269C of DIIIS6 was detected in 93% of field strains of Ae. aegypti. Various permutations of wild type and mutant amino acids of the four alleles were found to result in varying degree of survival rate among local field Ae. aegypti when exposed to the deltamethrin treated net. Together with the association of higher survival rate with the presence of both V1016G and F1269C, the data suggest the role of these mutations in the resistance to the deltamethrin. The high prevalence of these mutations were confirmed in a country wide survey where 70% and 72% of the 201 Ae. aegypti analysed possessed the mutations at residues 1016 and 1269 respectively. The highest mutated frequency combination was found to be heterozygous alleles (VG/FC) at both residues 1016 and 1269 (37.8%), followed by homozygous mutation at allele 1269 (24.4%) and homozygous mutation at allele 1016 (22.9%). The kdr- type of resistance among the vector is likely to undermine the effectiveness of pyrethroids treated materials against these mosquitoes.

Matched MeSH terms: Sodium Channels/genetics*
Fulltext Mechanical Strain-Mediated Tenogenic Differentiation of Mesenchymal Stromal Cells Is Regulated through Epithelial Sodium Channels

Nam HY, Murali MR, Ahmad RE, Pingguan-Murphy B, Raghavendran HRB, Kamarul T

Stem Cells Int, 2020;2020:5385960.
PMID: 32908542 DOI: 10.1155/2020/5385960

It has been suggested that mechanical strain may elicit cell differentiation in adult somatic cells through activation of epithelial sodium channels (ENaC). However, such phenomenon has not been previously demonstrated in mesenchymal stromal cells (MSCs). The present study was thus conducted to investigate the role of ENaC in human bone marrow-derived MSCs (hMSCs) tenogenic differentiation during uniaxial tensile loading. Passaged-2 hMSCs were seeded onto silicone chambers coated with collagen I and subjected to stretching at 1 Hz frequency and 8% strain for 6, 24, 48, and 72 hours. Analyses at these time points included cell morphology and alignment observation, immunocytochemistry and immunofluorescence staining (collagen I, collagen III, fibronectin, and N-cadherin), and gene expression (ENaC subunits, and tenogenic markers). Unstrained cells at similar time points served as the control group. To demonstrate the involvement of ENaC in the differentiation process, an ENaC blocker (benzamil) was used and the results were compared to the noninhibited hMSCs. ENaC subunits' (α, β, γ, and δ) expression was observed in hMSCs, although only α subunit was significantly increased during stretching. An increase in tenogenic genes' (collagen1, collagen3, decorin, tenascin-c, scleraxis, and tenomodulin) and proteins' (collagen I, collagen III, fibronectin, and N-cadherin) expression suggests that hMSCs underwent tenogenic differentiation when subjected to uniaxial loading. Inhibition of ENaC function resulted in decreased expression of these markers, thereby suggesting that ENaC plays a vital role in tenogenic differentiation of hMSCs during mechanical loading.

Matched MeSH terms: Epithelial Sodium Channels
Protein kinase D2 regulates epithelial sodium channel activity and aldosterone non-genomic responses in renal cortical collecting duct cells

Thomas W, Dooley R, Quinn S, Robles MY, Harvey BJ

Steroids, 2020 03;155:108553.
PMID: 31836481 DOI: 10.1016/j.steroids.2019.108553

Protein kinase D2 (PKD2) is a serine/threonine protein kinase which plays an important role in vesicle fission at the trans-Golgi network (TGN) to coordinate subcellular trafficking with gene expression. We found that in the rat kidney, PKD2 is specifically expressed in collecting duct principal cells predominantly at the apical membrane and with lower basal expression in cytosolic compartments. When rats were maintained on a Na+ depleted diet (<0.87 mmol Na+/kg) to increase plasma aldosterone levels, PKD2 became internalized to a cytoplasmic compartment. Treatment of murine M1 cortical collecting duct (M1-CCD) cells with aldosterone (10 nM) promoted PKD2 co-localization with the trans-Golgi network within 30 min. PKD2 underwent autophosphorylation at Ser876 within 10 min of aldosterone treatment and remained phosphorylated (active) for at least 24 h. A stable PKD2 shRNA knock-down (PKD2 KD) M1-CCD cell line was developed to study the role of PKD2 in epithelial Na+ channel (ENaC) trafficking and transepithelial Na+ transport (SCC) in epithelial monolayers grown in Ussing chambers. The PKD2 KD cells developed transepithelial resistance with kinetics equivalent to wild-type cells, however the transepithelial voltage and Na+ current were significantly elevated in PKD2 knock-down CCD epithelia. The higher basal SCC was due to increased ENaC activity. Aldosterone treatment for 24 h resulted in a decline in ENaC activity in the PKD2 KD cells as opposed to the increase observed in the wild-type cells. The paradoxical inhibition of SCC by aldosterone in PKD2 KD epithelium was attributed to a reduction in ENaC current and lower membrane abundance of ENaC, demonstrating that PKD2 plays a critical tonic role in ENaC trafficking and channel subunit stability. The rapid activation of PKD2 by aldosterone is synergistic with the transcriptional activity of MR and contributes to increased ENaC activity.

Matched MeSH terms: Epithelial Sodium Channels/metabolism*
Response to: Depolarization vs. repolarization: what is the mechanism of ventricular arrhythmogenesis underlying sodium channel haploinsufficiency in mouse hearts?

Jeevaratnam K, Guzadhur L, Goh YM, Grace AA, Huang CL

Acta Physiol (Oxf), 2016 12;218(4):236-238.
PMID: 27272698 DOI: 10.1111/apha.12731
Matched MeSH terms: Sodium Channels/genetics*
SCN1A, SCN2A and SCN3A gene polymorphisms and responsiveness to antiepileptic drugs: a multicenter cohort study and meta-analysis

Haerian BS, Baum L, Kwan P, Tan HJ, Raymond AA, Mohamed Z

Pharmacogenomics, 2013 Jul;14(10):1153-66.
PMID: 23859570 DOI: 10.2217/pgs.13.104

Aim: Approximately a third of newly diagnosed epilepsy patients do not respond to antiepileptic drugs (AEDs). Evidence suggests that low penetrance variants in the genes of drug targets such as voltage-gated sodium channels may be involved in drug responsiveness. To examine this hypothesis, we compared data from two epilepsy cohorts from Malaysia and Hong Kong, as well as a meta-analysis from published data.

Materials & methods: Genotype analysis of 39 polymorphisms located in the SCN1A, SCN2A and SCN3A genes was performed on 1504 epilepsy patients from Malaysia and Hong Kong who were receiving AEDs. Meta-analysis was performed for pooled data of SCN1A rs3812718 and rs2298771, and SCN2A rs17183814 polymorphisms.

Results: Our data from the Hong Kong and Malaysia cohorts showed no significant allele, genotype and haplotype association of polymorphisms in the SCN1A, SCN2A, and SCN3A genes with drug responsiveness in epilepsy. This finding was supported by a meta-analysis for SCN1A rs3812718 and rs2298771, and for SCN2A rs17183814 polymorphisms.

Conclusion: Our comprehensive study suggests that common polymorphisms in SCN1A, SCN2A and SCN3A do not play major roles in influencing response to AEDs.

Matched MeSH terms: Sodium Channels/genetics*
Fulltext Sodium channel biophysics, late sodium current and genetic arrhythmic syndromes

Chadda KR, Jeevaratnam K, Lei M, Huang CL

Pflugers Arch., 2017 06;469(5-6):629-641.
PMID: 28265756 DOI: 10.1007/s00424-017-1959-1

Arrhythmias arise from breakdown of orderly action potential (AP) activation, propagation and recovery driven by interactive opening and closing of successive voltage-gated ion channels, in which one or more Na+ current components play critical parts. Early peak, Na+ currents (I Na) reflecting channel activation drive the AP upstroke central to cellular activation and its propagation. Sustained late Na+ currents (I Na-L) include contributions from a component with a delayed inactivation timecourse influencing AP duration (APD) and refractoriness, potentially causing pro-arrhythmic phenotypes. The magnitude of I Na-L can be analysed through overlaps or otherwise in the overall voltage dependences of the steady-state properties and kinetics of activation and inactivation of the Na+ conductance. This was useful in analysing repetitive firing associated with paramyotonia congenita in skeletal muscle. Similarly, genetic cardiac Na+ channel abnormalities increasing I Na-L are implicated in triggering phenomena of automaticity, early and delayed afterdepolarisations and arrhythmic substrate. This review illustrates a wide range of situations that may accentuate I Na-L. These include (1) overlaps between steady-state activation and inactivation increasing window current, (2) kinetic deficiencies in Na+ channel inactivation leading to bursting phenomena associated with repetitive channel openings and (3) non-equilibrium gating processes causing channel re-opening due to more rapid recoveries from inactivation. All these biophysical possibilities were identified in a selection of abnormal human SCN5A genotypes. The latter presented as a broad range of clinical arrhythmic phenotypes, for which effective therapeutic intervention would require specific identification and targeting of the diverse electrophysiological abnormalities underlying their increased I Na-L.

Matched MeSH terms: Voltage-Gated Sodium Channels/genetics; Voltage-Gated Sodium Channels/metabolism*; Voltage-Gated Sodium Channels/chemistry
Fulltext Study of Visual Function in Adult Epileptic Patients on Sodium Valproate or Carbamazepine Monotherapy

Matthew TJH, Tharakan J, Tai E, Hussein A

Cureus, 2019 Apr 27;11(4):e4553.
PMID: 31275777 DOI: 10.7759/cureus.4553

Objective Epilepsy is a debilitating disease. Visual function changes have been reported and may be attributed to the epileptic changes or as a result of medication side effect. Sodium valproate and carbamazepine are both first line anti-epileptic medications used in Malaysian health care. Sodium valproate inhibits glutamate and γ-aminobutyric acid (GABA) transaminase while carbamazepine acts on the sodium channel - both are an important part of the retina. This study aimed to compare the visual functions of epilepsy patients on carbamazepine or sodium valproate monotherapy. Design A cross-sectional study was conducted at a tertiary hospital between June 2016 and November 2018. Methods Patients with idiopathic epilepsy that fulfill the inclusion and exclusion criteria were recruited from the neurology clinic. They were divided into two groups and underwent complete eye examinations. Visual functions such as color vision testing, contrast sensitivity, visual field and retinal nerve fiber layer measurement were subsequently performed. Statistical analysis was done using Statistical Package for the Social Science, version 24 (SPSS Inc, Chicago, IL, USA). Results A total of 100 patients (sodium valproate: 50 patients; carbamazepine: 50 patients) were recruited for the study. There were no statistically significant changes in anatomical or visual function between the sodium valproate and carbamazepine group. However, patients from both groups displayed color vision defect in the blue and green axes. Changes in color vision could indicate early retina toxicity secondary to the medication. Although there were no visual field changes, patients recorded a slight reduction of mean deviation. Changes of mean deviation could be attributed to the side effect of medication or the disease process. Conclusions Epileptic patients taking sodium valproate or carbamazepine did not demonstrate statistically significant change in visual function.

Matched MeSH terms: Sodium Channels

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