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:7720699, PubMed:17167479, PubMed:25240195, PubMed:26680203, PubMed:15385606, PubMed:16988069, PubMed:17145499, PubMed:19369487, PubMed:24311784). It is a tetrodotoxin-sensitive Na(+) channel isoform (PubMed:7720699). Plays a role in pain mechanisms, especially in the development of inflammatory pain (PubMed:17167479, PubMed:17145499, PubMed:19369487, PubMed:24311784). Inhibited by tetrodotoxin (PubMed:23077250). Weakly inhibited by saxitoxin (PubMed:23077250). The sodium channel complex consists of a large, channel-forming alpha subunit (SCN9A) regulated by one or more beta subunits (SCN1B, SCN2B, SCN3B and SCN4B) (PubMed:7720699, PubMed:17167479, PubMed:25240195). SCN1B and SCN3B are non-covalently associated with SCN2A. SCN2B and SCN4B are disulfide-linked to SCN2A. Interacts with NEDD4 and NEDD4L (By similarity). Interacts with the scorpion alpha-toxin CvIV4 (PubMed:21887265). Interacts with the conotoxin GVIIJ (PubMed:24497506). Interacts with the spider huwentoxin-IV (through the extracellular loop S3-S4 of repeat II) (PubMed:20855463, PubMed:21659528, PubMed:30661758, PubMed:30765606). Interacts with the spider protoxin-II (through the extracellular loop S3-S4 of repeats II and IV) (PubMed:20855463, PubMed:21659528, PubMed:30661758, PubMed:30765606). Interacts with the spider beta/delta-theraphotoxin-Pre1a (PubMed:28428547). In neurite terminals. Expressed strongly in dorsal root ganglion, with only minor levels elsewhere in the body, smooth muscle cells, MTC cell line and C-cell carcinoma. Also expressed in vagus nerves within the head and neck region (PubMed:31647222). Isoform 1 is expressed preferentially in the central and peripheral nervous system. Isoform 2 is expressed preferentially in the dorsal root ganglion. 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. Phosphorylation at Ser-1490 by PKC in a highly conserved cytoplasmic loop increases peak sodium currents. Ubiquitinated by NEDD4L; which may promote its endocytosis. Does not seem to be ubiquitinated by NEDD4. 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. Belongs to the sodium channel (TC 1.A.1.10) family. Nav1.7/SCN9A subfamily. SCN9A has been originally reported to be involved in generalized epilepsy with febrile seizures plus (GEFS+)(PubMed:19763161). However, it has later been shown that SCN9A variants are not a likely cause of autosomal dominant febrile seizures/febrile seizures plus and other monogenic seizure phenotypes (PubMed:33216760). SCN9A entry Silent pain - Issue 102 of February 2009