Voltage gated sodium channel, alpha-8 subunit (IPR008054)
Short name: Na_channel_a8su
Overlapping homologous superfamilies
- Voltage gated sodium channel, alpha subunit (IPR001696)
- Voltage gated sodium channel, alpha-8 subunit (IPR008054)
Voltage-dependent sodium channels are transmembrane (TM) proteins responsible for the depolarising phase of the action potential in most electrically excitable cells [PMID: 1317577]. They may exist in 3 states [PMID: 1323284]: 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.
The structure of sodium channels is based on 4 internal repeats of a 6-helix bundle [PMID: 6209577] (in which 5 of the membrane-spanning segments are hydrophobic and the other is positively charged), forming a 24-helical bundle. The charged segments are believed to be localised within clusters formed by their 5 hydrophobic neighbours: it is postulated that the charged domain may be the voltage sensor region, possibly moving outward on depolarisation, causing a conformational change. This model [PMID: 6209577] contrasts with another [PMID: 1323284], in which the TM segments are juxtaposed octagonally. The basic structural motif (the 6-helix bundle) is also found in potassium and calcium channel alpha subunits.
The gene SCN8A encodes the voltage-gated Na+ channel alpha 8 subunit and is strongly expressed in Purkinje cells. Sodium currents are known to generate the rising phase and the prolonged plateau phase of cerebellar purkinje cell action potentials. Experiments in mice with mutated SCN8A subunits suggest its involvement in the persistent sodium current responsible for the prolonged plateau phase [PMID: 9192691]. The SCN8A gene is abundantly expressed throughout the CNS and in the spinal cord. Mutations in mouse SCN8A result in a number of neurological disorders, including paralysis, ataxia and dystonia [PMID: 9698304].
This entry represents a conserved region found towards the N terminus of the protein, which defines the alpha 8 subunits and distinguishes them from other members of the voltage-gated Na+ channel superfamily. For entries containing other members of this superfamily see IPR008051, IPR008052, IPR008053.
- PR01667 (NACHANNEL8)