title: Voltage-sensitive sodium channels: an evolving molecular view.
abstract: Sodium channel proteins have now been isolated from a number of nerve and muscle preparations. All are characterized by the presence of a very large glycoprotein subunit of approximately 260 kilodaltons which may contain the structural features required for voltage-dependent channel gating and cation selectivity. These purified proteins have been reconstituted into vesicle systems and planar bilayers and demonstrate the ensemble and single-channel behavior characteristic of the native sodium channel. Although the sodium channel from eel appears to consist of only the 260-kilodalton protein, the channels from rat brain and rat or rabbit skeletal muscle contain one or more smaller subunits of 37-39 kilodaltons. In skeletal muscle, a 38-kilodalton subunit is present in both conventionally purified channel and channel isolated with immunoaffinity techniques. The stoichiometry of the large (alpha) and the small (beta) subunits appears to be 1:1 in skeletal muscle but 1:2 in rat brain. The role of the small subunits in the normal functioning of the sodium channel remains to be defined.
mesh_terms: D000818:Animals; D002241:Carbohydrates / Q000032:analysis; D006023:Glycoproteins / Q000032:analysis; D007473:Ion Channels / Q000145:classification / Q000187:drug effects / Q000502:physiology*; D046911:Macromolecular Substances; D008564:Membrane Potentials; D008970:Molecular Weight; D009132:Muscles; D011817:Rabbits; D012964:Sodium / Q000502:physiology*
chemical_list: D002241:Carbohydrates; D006023:Glycoproteins; D007473:Ion Channels; D046911:Macromolecular Substances; D012964:Sodium