FUNCTION: SwissProt: Q14524 # This protein mediates the voltage-dependent sodium ion permeability of excitable membranes. Assuming opened or closed conformations in response to the voltage difference across the membrane, the protein forms a sodium-selective channel through which Na(+) ions may pass in accordance with their electrochemical gradient. It is a tetrodotoxin-resistant Na(+) channel isoform. This channel is responsible for the initial upstroke of the action potential in the electrocardiogram.
SIZE: 2016 amino acids; 227162 Da
SUBUNIT: Interacts with the PDZ domain of the syntrophin SNTA1, SNTB1 and SNTB2 (By similarity). Interacts with NEDD4, NEDD4L and WWP2.
SUBCELLULAR LOCATION: Membrane; Multi-pass membrane protein.
TISSUE SPECIFICITY: Expressed in human atrial and ventricular cardiac muscle but not in adult skeletal muscle, brain, myometrium, liver, or spleen.
DOMAIN: SwissProt: Q14524 The sequence contains 4 internal repeats, each with 5 hydrophobic segments (S1,S2,S3,S5,S6) and one positively charged segment (S4). Segments S4 are probably the voltage-sensors and are characterized by a series of positively charged amino acids at every third position.
PTM: Ubiquitinated by NEDD4L; which promotes its endocytosis. Does not seem to be ubiquitinated by NEDD4 or WWP2.
DISEASE: SwissProt: Q14524 # Defects in SCN5A are a cause of progressive familial heart block type I (PFHBI) [MIM:113900]; also known as Lenegre-Lev disease or progressive cardiac conduction defect (PCCD). PFHBI is characterized by progressive alteration of cardiac conduction through the His-Purkinje system with right or left bundle branch block and widening of QRS complexes, leading to complete atrio- ventricular block and causing syncope and sudden death. PFHBI inheritance is autosomal dominant. & Defects in SCN5A are the cause of long QT syndrome type 3 (LQT3) [MIM:603830]. Long QT syndromes are heart disorders characterized by a prolonged QT interval on the ECG and polymorphic ventricular arrhythmias. They cause syncope and sudden death in response to exercise or emotional stress. LQT3 inheritance is an autosomal dominant. & Defects in SCN5A are the cause of Brugada syndrome [MIM:601144]. Brugada syndrome is an autosomal dominant inherited arrhythmia that causes the ventricles to beat so fast that they can prevent the blood from circulating efficiently in the body. When this situation occurs (called ventricular fibrillation), the individual will faint and may die in a few minutes if the heart is not reset. Brugada syndrome is an idiopathic ventricular fibrillation (IVF) syndrome characterized by right bundle branch block and ST elevation on an electrocardiogram (ECG). While Brugada syndrome is a disease that usually affects people in their 30's, it has actually been described at all ages. & Defects in SCN5A are the cause of autosomal recessive sick sinus syndrome 1 (SSS1) [MIM:608567]. The term 'sick sinus syndrome' encompasses a variety of conditions caused by sinus node dysfunction. The most common clinical manifestations are syncope, presyncope, dizziness, and fatigue. Electrocardiogram typically shows sinus bradycardia, sinus arrest, and/or sinoatrial block. Episodes of atrial tachycardias coexisting with sinus bradycardia ('tachycardia-bradycardia syndrome') are also common in this disorder. SSS occurs most often in the elderly associated with underlying heart disease or previous cardiac surgery, but can also occur in the fetus, infant, or child without heart disease or other contributing factors, in which case it is considered to be a congenital disorder. & Defects in SCN5A are a cause of idiopathic ventricular fibrillation (IVF) [MIM:603829]; also called paroxysmal familial ventricular fibrillation. IVF is a self originated, of unknown causation, ventricular fibrillation that causes the ventricles to beat so fast that they can prevent the blood from circulating efficiently in the body. This disorder is not truly idiopathic in many cases but can be caused by specific mutations such as those in the SCN5A gene. IVF is said to cause more than 300,000 sudden deaths each year in the United States alone. In approximately 5 to 12% of cases, there are no demonstrable cardiac or non-cardiac causes to account for the episode, which is therefore classified as idiopathic ventricular fibrillation. & Defects in SCN5A are a cause of sudden infant death syndrome (SIDS) [MIM:272120]. SIDS remains elusive in its causes and devastating in its consequences. Despite the impressive decline in the incidence of SIDS since the recommendation to avoid the prone sleep position, SIDS remains a leading cause of death in the first year of life. & Defects in SCN5A may be a cause of familial atrial standstill [MIM:108770]. Atrial standstill is an extremely rare arrhythmia, characterized by the absence of electrical and mechanical activity in the atria. Electrocardiographically, it is characterized by bradycardia, the absence of P waves, and a junctional narrow complex escape rhythm. & Defects in SCN5A are the cause of dilated cardiomyopathy 1E (CMD1E) [MIM:601154]; also known as dilated cardiomyopathy with conduction disorder and arrhythmia or dilated cardiomyopathy with conduction defect 2. CMD1E is characterized by autosomal dominant transmission, young age of onset, arrhythmia and conduction disorder that culminates, in most cases, in biatrial and biventricular dilation.
SIMILARITY: Belongs to the sodium channel family. & Contains 1 IQ domain.
MISCELLANEOUS: Na(+) channels in mammalian cardiac membrane have functional properties quite distinct from Na(+) channels in nerve and skeletal muscle.