Mediates the voltage-dependent sodium ion permeability of excitable membranes. Assuming opened or closed conformations in response to the voltage difference across the membrane, forms a sodium-selective channel through which Na(+) ions may pass in accordance with their electrochemical gradient (PubMed:24157691, PubMed:28235671, PubMed:29466837). May contribute to the regulation of serotonin/5-hydroxytryptamine release by enterochromaffin cells (By similarity). In pancreatic endocrine cells, required for both glucagon and glucose-induced insulin secretion (By similarity). Heterooligomer of a large alpha subunit and 2-3 smaller beta subunits. Heterooligomer with SCN2B or SCN4B; disulfide-linked. Interacts with NEDD4L (PubMed:15548568). Interacts with the conotoxin GVIIJ (PubMed:24497506). Exons 6A and 6N only differ by a single residue. Expressed in enterochromaffin cells in both colon and small bowel (at protein level). 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-1501 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. Belongs to the sodium channel (TC 1.A.1.10) family. Nav1.3/SCN3A subfamily.