| Modification Notes |
L-type (long lasting current) voltage-dependent calcium channels are composed of four subunits, designated å1, ∫, © and å2/∂, all of which work together to mediate neurotransmitter release. The å subunit contains a tetrameric association of four domains each containing a series of six transmembrane å-helical segments, numbered S1–S6, which are connected by both intracellular and extracellular loops. The å subunit is comprised of an ion-conducting pore, which determines the main characteristics of the cation channel complex, including ion selectivity, voltage sensitivity and pharmacology, and binding characteristics for endogenous and exogenous ligands. There are ten genes in the human genome that encode pore-forming å1 subunits of voltage-gated calcium channels. In combination with accessory subunits, these ten å1 subunits, which include L-type Ca++ CP å1S, 1C, 1D and 1F, must mediate diverse functions such as intracellular calcium homeostasis, regulation of gene expression and coupling of membrane potential changes to various downstream processes like neurotransmitter release or muscle contraction. |