Voltage-dependent sodium channels are transmembrane (TM) proteins responsible for the depolarising phase of the action potential in mostelectrically excitable cells []. They may exist in 3 states []: the resting state, where the channel is closed; the activated state, where the channel is open; and the inactivated state, where the channel is closed and refractory to opening. Several different structurally and functionally distinct isoforms are found in mammals, coded for by a multigene family, these being responsible for the different types of sodium ion currents found in excitable tissues.There are nine pore-forming alpha subunit of voltage-gated sodium channels consisting of four membrane-embedded homologous domains (I-IV), each consisting of six α-helical segments (S1-S6), three cytoplasmic loops connecting the domains, and a cytoplasmic C-terminal tail. The S6 segments of the four domains form the inner surface of the pore, while the S4 segments bear clusters of basic residues that constitute the channel's voltage sensors [, , ].The SCN1A gene encodes the NaB1 channel and is particularly expressed inthe brain, but is also found in a variety of other tissues, ranging from theretina to the olfactory bulb. Epilepsy, a disorder of neuronalhyperexcitability, has been associated with altered kinetics of SCN1A, aswell as delayed inactivation of SCN2A [].This entry represents the alpha 1 subunits of the voltage-gated Na+ channel superfamily. For entries containing other members of this superfamily see , , .
