OBJECTIVETo detect the expression of voltage-gated Na(+) channel (NaCh) isoforms in rat sinoatrial node and explore their functions.

METHODSExpressions of NaCh isoforms Nav1.1, Nav1.2, Nav1.3, Nav1.5, Nav1.6 and Nav1.7 in the rat sinoatrial node were detected by immunohistochemistry. The functional roles of the NaChs were tested by observing the effect of tetrodotoxin, a specific blocker of NaChs, on the intrinsic heart rate of isolated rat working heart.

RESULTSThe tetrodotoxin- sensitive neuronal isoforms Nav1.1, Nav1.6 and Nav1.7 as well as the tetrodotoxin-resistant cardiac isoform Nav1.5 were present in the rat sinoatrial node, and the neuronal isoforms were more abundant than Nav1.5 (P<0.05). The selective blockade of tetrodotoxin-sensitive isoforms (presumably Nav1.1, Nav1.6 and Nav1.7) by 100 nmol/L tetrodotoxin scarcely affected the intrinsic heart rate (0.5-/+2.9%, P>0.05) while blockade of tetrodotoxin-resistant isoform (presumably Nav1.5) by 2 micromol/L tetrodotoxin resulted in an obvious decline in the intrinsic heart rate (22.1-/+2.1%, P<0.001).

CONCLUSIONSNav1.1, Nav1.5, Nav1.6 and Nav1.7 are all present in rat sinoatrial node. Although neuronal isoforms are more abundant, Nav1.5 seems to contribute more to activity of the sinoatrial node.

Animals ; Heart Rate ; drug effects ; physiology ; Immunohistochemistry ; Ion Channel Gating ; drug effects ; physiology ; Male ; NAV1.1 Voltage-Gated Sodium Channel ; NAV1.5 Voltage-Gated Sodium Channel ; NAV1.6 Voltage-Gated Sodium Channel ; Nerve Tissue Proteins ; biosynthesis ; Protein Isoforms ; biosynthesis ; Rats ; Sinoatrial Node ; drug effects ; metabolism ; physiology ; Sodium Channels ; biosynthesis ; Tetrodotoxin ; pharmacology

Voltage-gated sodium (Na) channels are essential for the rapid upstroke of action potentials and the propagation of electrical signals in nerves and muscles. Defects of Na channels are associated with a variety of channelopathies. More than 1000 disease-related mutations have been identified in Na channels, with Na1.1 and Na1.5 each harboring more than 400 mutations. Na channels represent major targets for a wide array of neurotoxins and drugs. Atomic structures of Na channels are required to understand their function and disease mechanisms. The recently determined atomic structure of the rabbit voltage-gated calcium (Ca) channel Ca1.1 provides a template for homology-based structural modeling of the evolutionarily related Na channels. In this Resource article, we summarized all the reported disease-related mutations in human Na channels, generated a homologous model of human Na1.7, and structurally mapped disease-associated mutations. Before the determination of structures of human Na channels, the analysis presented here serves as the base framework for mechanistic investigation of Na channelopathies and for potential structure-based drug discovery.
Animals ; Calcium Channels, L-Type ; chemistry ; genetics ; metabolism ; Channelopathies ; genetics ; metabolism ; Humans ; Mutation ; NAV1.1 Voltage-Gated Sodium Channel ; chemistry ; genetics ; metabolism ; NAV1.5 Voltage-Gated Sodium Channel ; chemistry ; genetics ; metabolism ; NAV1.7 Voltage-Gated Sodium Channel ; chemistry ; genetics ; metabolism ; Protein Domains ; Rabbits ; Structure-Activity Relationship

A new method of axon recording through axon bleb has boosted the studies on the functional role of central nervous system (CNS) axons. Using this method, we have revealed the mechanisms underlying the initiation and propagation of the digital-mode signal, all-or-none action potentials (APs), in neocortical pyramidal neurons. Accumulation of the low-threshold Na(+) channel subtype Na(v)1.6 at the distal end of the axon initial segment (AIS) determines the lowest threshold for AP initiation, whereas accumulation of the high-threshold subtype Na(v)1.2 at the proximal region of the AIS promotes AP backpropagation to the soma and dendrites. Through dual recording from the soma and the axon, we have showed that subthreshold membrane potential (V(m)) fluctuations in the soma propagate along the axon to a long distance and probably reach the axon terminals. Paired recording from cortical neurons has revealed that these V(m) changes in the soma modulate AP-triggered synaptic transmission. This new V(m)-dependent mode of synaptic transmission is called analog communication. Unique properties of axonal K(+) channels (K(v)1 channels) may contribute to shaping the AP waveform, particularly its duration, and thus controlling synaptic strength at different levels of presynaptic V(m). The level of background Ca(2+) may also participate in mediating the analog signaling. Together, these findings enrich our knowledge on the principles of neuronal signaling in the CNS and help understand how the brain works.
Action Potentials ; physiology ; Animals ; Axons ; physiology ; Central Nervous System ; cytology ; physiology ; Humans ; Membrane Potentials ; physiology ; NAV1.2 Voltage-Gated Sodium Channel ; physiology ; NAV1.6 Voltage-Gated Sodium Channel ; physiology ; Neocortex ; cytology ; physiology ; Patch-Clamp Techniques ; Pyramidal Cells ; physiology ; Sodium Channels ; physiology

Epilepsy is one of the most common and debilitating neurological diseases that affects more than 40 million people worldwide. Genetic factors contribute to the pathogenesis of epilepsy. Molecular genetic studies have identified 15 disease-causing genes for epilepsy. The majority of the genes encode ion channels, including voltage-gated potassium channels KCNQ2 and KCNQ3, sodium channels SCN1A, SCN2A, and SCN1B, chloride channels CLCN2, and ligand-gated ion channels CHRNA4, CHRNB2, GABRG2, and GABRA1. Interestingly, non-ion channel genes have also been identified as epilepsy genes, and these genes include G-protein-coupled receptor MASS1/VLGR1, GM3 synthase, and proteins with unknown functions such as LGI1, NHLRC1, and EFHC1. These studies make genetic testing possible in some patients, and further characterization of the identified epilepsy genes may lead to the development of new drugs and new treatments for patients with epilepsy.
Chloride Channels ; genetics ; Epilepsies, Myoclonic ; genetics ; Epilepsy ; genetics ; Epilepsy, Absence ; genetics ; Humans ; KCNQ2 Potassium Channel ; genetics ; KCNQ3 Potassium Channel ; genetics ; NAV1.1 Voltage-Gated Sodium Channel ; NAV1.2 Voltage-Gated Sodium Channel ; Nerve Tissue Proteins ; genetics ; Sodium Channels ; genetics

Epilepsy is a group of disorders characterized by recurrent seizures. The etiologies of idiopathic epilepsy commonly have a genetic basis. Gene mutations causing several of the inherited epilepsies have been mapped. In this review, the authors summarize the available information on the genetic basis of human epilepsies and epilepsy syndromes, emphasizing how genetic defects may correlate with the pathophysiological mechanisms of brain hyperexcitability and gene defects can lead to epilepsy by altering multiple and diverse aspects of neuronal function.
Epilepsy ; genetics ; Humans ; KCNQ2 Potassium Channel ; Mutation ; NAV1.1 Voltage-Gated Sodium Channel ; Nerve Tissue Proteins ; genetics ; Potassium Channels ; genetics ; Potassium Channels, Voltage-Gated ; Receptors, Nicotinic ; genetics ; Research ; trends ; Research Design ; Sodium Channels ; genetics ; Voltage-Gated Sodium Channel beta-1 Subunit

Cardiomyopathy, Dilated ; genetics ; Humans ; NAV1.5 Voltage-Gated Sodium Channel ; Sodium Channels ; genetics

This study is to explore a new method of investigating molecular basis for electrophysiological properties of early fetal cardiomyocytes. Single embryonic cardiomyocytes of mouse early developmental heart (E10.5) were obtained by a collagenase B digestion approach. After recording spontaneous action potential using whole cell patch clamp technique, the single cell was picked by a glass micropipette, followed by a standard RT-PCR to explore the expression levels of several ion channel genes. Three phenotypes of cardiomyocytes were demonstrated with distinct properties: ventricular-like, atrial-like, and pacemaker-like action potentials. Ventricular-like and atrial-like cells were characterized with much negative maximum diastolic potential (MDP) and a higher V(max) (maximum velocity of depolarization) compared to pacemaker-like cells. MDP of ventricular-like cells was the most negative. In parallel, stronger expression of SCN5a, SCN1b and Kir2.1 were observed in ventricular-like and atrial-like cells compared to that of pacemaker-like cells, where Kir2.1 in ventricular-like cells was the most abundant. Cardiomyocytes with distinct electrophysiological properties had distinct gene expression pattern. Single cell RT-PCR combined with patch clamp technique could serve as a precise detector to analyze the molecular basis of the special electrophysiological characteristics of cardiomyocytes.
Animals ; Electrophysiological Phenomena ; Female ; Fetus ; Male ; Mice ; Myocytes, Cardiac ; metabolism ; physiology ; NAV1.5 Voltage-Gated Sodium Channel ; genetics ; metabolism ; Patch-Clamp Techniques ; Potassium Channels, Inwardly Rectifying ; genetics ; metabolism ; Real-Time Polymerase Chain Reaction ; Voltage-Gated Sodium Channel beta-1 Subunit ; genetics ; metabolism

OBJECTIVEThree long QT syndrome(LQTS) pedigrees were brought together for genetic diagnosis by using short tandem repeat(STR) markers.

METHODSGenomic DNA was extracted from blood samples. STR markers (D7S1824, D7S2439, D7S483, D3S1298, D3S1767, D3S3521) in or spanning the HERG and SCN5A gene were amplified; the haplotype analysis for LQTS was performed.

RESULTSClinical diagnosis showed that 15 are LQTS patients (3 died) and 11 are probable patients. Linkage analysis showed that LQTS patients are linked with the SCN5A gene in family 1, HERG is linked with the disease in family 2 and 3. Fourteen gene carriers were identified, 2 patients and 7 probable patients were excluded.

CONCLUSIONLinkage analysis using STR markers can serve as useful tool for presymptomatic diagnosis.

ERG1 Potassium Channel ; Ether-A-Go-Go Potassium Channels ; Female ; Genetic Linkage ; Haplotypes ; Humans ; Long QT Syndrome ; genetics ; Male ; NAV1.5 Voltage-Gated Sodium Channel ; Pedigree ; Potassium Channels ; genetics ; Potassium Channels, Voltage-Gated ; Sodium Channels ; genetics ; Tandem Repeat Sequences

BACKGROUNDMutations in the cardiac sodium channel gene (SCN5A) may lead to a broad spectrum of familial arrhythmias, including long QT syndrome (LQTS), idiopathic ventricular fibrillation (IVF), and isolated cardiac conduction diseases. Recent studies have shown that polymorphisms in the SCN5A gene also play an important role in the manifestation of disorders involving cardiac excitability. In this study, we investigated the polymorphisms of the SCN5A gene in Han Chinese and its relation to Brugada syndrome (BS).

METHODSGenomic DNA was isolated from 120 unrelated healthy volunteers and 48 unrelated Brugada syndrome patients by means of standard procedures. All exons including the putative splicing sites of the SCN5A gene were amplified by PCR and sequenced directly or after subcloning using an ABI Prism 377 DNA sequencer.

RESULTSA total of 5 single nucleotide polymorphisms (SNPs) were identified in the Han Chinese population, including 3 novel ones: G87A(A29A), 4245 + 82A > G, and G6174A. The allele frequencies of each SNP in the Han Chinese population were as follows: G87A (A29A) 27.5%, A1673G (H558R) 10.4%, 4245 + 82A > G 32.8%, C5457T (D1819D) 41.3%, and G6174A 44.9%. S1102Y and 10 other SNPs identified in other ethnic populations were not detected in this study. There was no significant difference in the allele frequency of A1673G (H558R) between different ethnic populations (all P > 0.5). On the other hand, the allele frequency of C5457T (D1819D) among Han Chinese was similar to its frequency among Japanese (P > 0.5), but higher than that among Americans (P < 0.005). The allele G1673 (R558) was over-represented in BS patients compared to controls (P < 0.005), but there was no significant difference in genotype frequencies at this locus. There were also no differences in either the allele or genotype frequencies of the 4 other identified SNPs when comparing BS patients with healthy controls.

CONCLUSIONSThe distribution of SCN5A SNPs may vary between different ethnicities. The polymorphism of A1673G might be associated with BS and may contribute to a susceptibility to BS in Han Chinese.

Case-Control Studies ; China ; ethnology ; Gene Frequency ; Humans ; NAV1.5 Voltage-Gated Sodium Channel ; Polymorphism, Single Nucleotide ; Sodium Channels ; genetics ; Syndrome ; Ventricular Fibrillation ; genetics

OBJECTIVEBrugada syndrome is an inherited channelopathy that characterized by ST-segment elevation in the right precordial lead (V(1)-V(3)) on the electrocardiogram with or without right bundle branch block and related with high risk of sudden cardiac death and structurally normal hearts. The first and only gene linked to this disease is SCN5A, a gene encodes for alpha subunit of the cardiac sodium channel. The objective of this study is to explore SCN5A gene mutations in Chinese patients with Brugada syndrome.

METHODSFour patients diagnosed as Brugada syndrome and nine patients with suspected Brugada syndrome were chosen for the study. The exons in the functional regions of SCN5A gene were amplified with polymerase chain reaction and the amplified products were sequenced with Sanger method. If a mutation was identified, patient's family members were also screened.

RESULTSTwo heterozygous mutations were found in one family diagnosed as Brugada syndrome. One missense mutation was a G-->A transition in the first nucleotide of codon 95 in SCN5A gene exon 3, which was predicted to result in substitution of Valine with Isoleucine (V95I). The other missense mutation was a C-->T transition in the second nucleotide of codon 1649 in SCN5A gene exon 28, which was predicted to result in substitution of Alanine with Valine (A1649V). A heterozygous mutation was identified in one family suspected to have the disease. The mutation was a three nucleotides (TCT) deletion that caused Phenylalanine deletion in codon 1617 in SCN5A gene exon 28. The three mutations were not detected in 100 control chromosomes.

CONCLUSIONSMutation in SCN5A gene is one of the causes of Brugada syndrome in Chinese. Three novel SCN5A gene mutations were identified in Chinese with Brugada syndrome, which expands the spectrum of SCN5A mutations associated with the disease.

Adolescent ; Adult ; Aged ; Brugada Syndrome ; genetics ; Case-Control Studies ; Exons ; genetics ; Humans ; Male ; Middle Aged ; Muscle Proteins ; genetics ; Mutation ; NAV1.5 Voltage-Gated Sodium Channel ; Sodium Channels ; genetics