Voltage-gated sodium channel
When accessory proteins assemble with α subunits, the resulting complex can display altered voltage dependence and cellular localization.
[2] When stimulated by a change in transmembrane voltage, this segment moves toward the extracellular side of the cell membrane, allowing the channel to become permeable to ions.
The inactivation gate can be thought of as a "plug" tethered to domains III and IV of the channel's intracellular alpha subunit.
This refractory period eliminates the possibility of an action potential moving in the opposite direction back towards the soma.
The refractory period of each channel is therefore vital in propagating the action potential unidirectionally down an axon for proper communication between neurons.
Mutations that interfere with Na+ channel inactivation can contribute to cardiovascular diseases or epileptic seizures by window currents, which can cause muscle and/or nerve cells to become over-excited.
The cations flow into a more constricted part of the pore that is 0.3 by 0.5 nm wide, which is just large enough to allow a single Na+ ion with a water molecule associated to pass through.
Ions of different sizes also cannot interact as well with the negatively charged glutamic acid residues that line the pore.
The family of sodium channels has 9 known members, with amino acid identity >50% in the trans-membrane segments and extracellular loop regions.
[10] The probable evolutionary relationship between these channels, based on the similarity of their amino acid sequences, is shown in figure 1.
Gastrointestinal: Irritable bowel syndrome;[15] Sodium channel beta subunits are type 1 transmembrane glycoproteins with an extracellular N-terminus and a cytoplasmic C-terminus.
[20] Sodium channels are more likely to stay open at the subthreshold membrane potential when interacting with beta toxins, which in turn induces an immediate sensation of pain.
[31] A voltage-gated sodium channel is present in members of the choanoflagellates, thought to be the closest living, unicellular relative of animals.
[36] The resulting four-domain channel is thought to have been permeable primarily for calcium, and to have achieved sodium selectivity a number of times independently.
[39][40] After the tetrapod/teleost split, the teleosts likely underwent a third WGD leading to the eight sodium channel prologues expressed in many modern fishes.
[39] The modern, ten-paralogue sodium gene complement of mammals is thought to have arisen from a series of parallel and nested duplications involving two of the four paralogues present in the ancestor of all tetrapods.
[41] This article incorporates text by Maryam Iman, Atefeh Saadabadi, and Asghar Davood available under the CC BY 4.0 license.
