[Structure, function and expression of Ca2+ channels]

Structure, function and expression of voltage-dependent Ca2+ channels are reviewed. Ca2+ channels have been classified into one low-voltage activated subtype (T type) and at least 5 high-voltage activated subtypes (L, N, P, Q and R types), which are characterized by the sensitivity to specific blockers. Although L-type channel in skeletal muscle is shown to consist of alpha1, alpha2/delta, beta, gamma subunits, it is not clear whether other subtypes have similar subunit structures. Cloning and functional expression of cDNA encoding alpha1 subunits revealed existence of multiple genes and splicing variants. Thus, the diversity in the electrophysiological properties of Ca2+ channels in different tissues and developmental stages comes from, at least in part, the different molecular structure of the channels. Regulation of the expression of Ca2+ channels may be important for the elaborate control of cellular functions.