Mediates the voltage-dependent sodium ion permeability of excitable membranes (PubMed:29726066). 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. In macrophages and melanoma cells, may participate in the control of podosome and invadopodia formation. The voltage-sensitive sodium channel consists of an ion conducting pore forming alpha-subunit regulated by one or more beta-1 (SCN1B), beta-2 (SCN2B), beta-3 (SCN3B) and/or beta-4 (SCN4B). Beta-1 (SCN1B) and beta-3 (SCN3B) are non-covalently associated with alpha, while beta-2 (SCN2B) and beta-4 (SCN4B) are covalently linked by disulfide bonds. Interacts with NEDD4 and NEDD4L (By similarity). Interacts with FGF13 (PubMed:33245860). Interacts with FGF14, GBG3, GBB2 and SCN1B (PubMed:26900580). Interacts with the conotoxin GVIIJ (PubMed:24497506). Interacts with the conotoxin GVIIJ (PubMed:24497506). Interacts with the spider beta/delta-theraphotoxin-Pre1a (PubMed:28428547). Interacts with CALM1; the interaction modulates the inactivation rate of SCN8A (By similarity). Mainly localizes to the axon initial segment. Some vesicles are localized adjacent to melanoma invadopodia and macrophage podosomes. Does not localize to the plasma membrane. Expressed in the hippocampus with increased expression in epileptic tissue compared to normal adjacent tissue (at protein level) (PubMed:28842554). Isoform 5: Expressed in non-neuronal tissues, such as monocytes/macrophages. Up-regulated in the hippocampus after epilepsy. 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. May be ubiquitinated by NEDD4L; which would promote its endocytosis. Phosphorylation at Ser-1497 by PKC in a highly conserved cytoplasmic loop slows inactivation of the sodium channel and reduces peak sodium currents. 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 may be caused by variants affecting the gene represented in this entry. Belongs to the sodium channel (TC 1.A.1.10) family. Nav1.6/SCN8A subfamily.