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 (PubMed:1309946, PubMed:21447824, PubMed:25370050, PubMed:23420830, PubMed:23085483, PubMed:26279430, PubMed:26392562, PubMed:26776555). It is a tetrodotoxin-resistant Na(+) channel isoform (PubMed:1309946). This channel is responsible for the initial upstroke of the action potential. Channel inactivation is regulated by intracellular calcium levels (PubMed:19074138). Interacts with the PDZ domain of the syntrophin SNTA1, SNTB1 and SNTB2 (By similarity). Interacts with NEDD4, NEDD4L, WWP2 and GPD1L (PubMed:15217910, PubMed:15548568, PubMed:19666841). Interacts with CALM (PubMed:21167176, PubMed:22705208, PubMed:25370050). Interacts with FGF13; the interaction is direct and FGF13 may regulate SNC5A density at membranes and function (PubMed:21817159, PubMed:22705208, PubMed:26392562). May also interact with FGF12 and FGF14 (PubMed:26392562). Interacts with the spider Jingzhaotoxin-I (AC P83974, AC B1P1B7, AC B1P1B8) (PubMed:26721415). Interacts with ANK3 (PubMed:15579534). RANGRF promotes trafficking to the cell membrane. Found in jejunal circular smooth muscle cells (at protein level). Expressed in human atrial and ventricular cardiac muscle but not in adult skeletal muscle, brain, myometrium, liver, or spleen. Isoform 4 is expressed in brain. 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. The IQ domain mediates association with calmodulin. Ubiquitinated by NEDD4L; which promotes its endocytosis. Does not seem to be ubiquitinated by NEDD4 or WWP2. Phosphorylation at Ser-1503 by PKC in a highly conserved cytoplasmic loop slows inactivation of the sodium channel and reduces peak sodium currents (Probable). Regulated through phosphorylation by CaMK2D (By similarity). Lacks the cysteine which covalently binds the conotoxin GVIIJ. This cysteine (position 868) is speculated in other sodium channel subunits alpha to be implied in covalent binding with the sodium channel subunit beta-2 or beta-4. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Disease susceptibility is associated with variants affecting the gene represented in this entry. The disease may be caused by variants affecting distinct genetic loci, including the gene represented in this entry. A mutation in SCN5A has been detected in combination with a rare GJA5 genotype in a large family with atrial standstill. The disease is caused by variants affecting the gene represented in this entry. The disease is caused by variants affecting the gene represented in this entry. Na(+) channels in mammalian cardiac membrane have functional properties quite distinct from Na(+) channels in nerve and skeletal muscle. Most abundant isoform in heart. Very abundant isoform. Abundantly expressed in neonatal brain and heart, slower kinetics of activation and inactivation. Only detected in neuroblastoma in humans. High expression in brain where it accounts for nearly 50% of the total transcripts. Non-functional channel, may exist to limit the number of undesired functional Nav1.5 channels. Belongs to the sodium channel (TC 1.A.1.10) family. Nav1.5/SCN5A subfamily.