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 sodium ions may pass in accordance with their electrochemical gradient. It is a tetrodotoxin-resistant sodium channel isoform. Also involved, with the contribution of the receptor tyrosine kinase NTRK2, in rapid BDNF-evoked neuronal depolarization. The voltage-resistant sodium channel consists of an ion conducting pore forming alpha-subunit regulated by one or more auxiliary subunits SCN1B, SCN2B and SCN3B. Expressed in the dorsal root ganglia and trigeminal ganglia, olfactory bulb, hippocampus, cerebellar cortex, spinal cord, spleen, small intestine and placenta. 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-1341 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. Nav1.9/SCN11A subfamily.