Structure and regulation of voltage-gated Ca$^2+$ channels.
Annu. Rev. Cell. Dev. Biol. (2000)

Voltage-gated Ca$^2+$ channels mediate Ca$^2+$ entry into cells in response to membrane depolarization. Electrophysiological studies reveal different Ca$^2+$ currents designated L-, N-, P-, Q-, R-, and T-type. The high-voltage-activated Ca$^2+$ channels that have been characterized biochemically are complexes of a pore-forming alpha1 subunit of approximately 190-250 kDa; a transmembrane, disulfide-linked complex of alpha2 and delta subunits; an intracellular beta subunit; and in some cases a transmembrane gamma subunit. Ten alpha1 subunits, four alpha2delta complexes, four beta subunits, and two gamma subunits are known. The Cav1 family of alpha1 subunits conduct L-type Ca$^2+$ currents, which initiate muscle contraction, endocrine secretion, and gene transcription, and are regulated primarily by second messenger-activated protein phosphorylation pathways. The Cav2 family of alpha1 subunits conduct N-type, P/Q-type, and R-type Ca$^2+$ currents, which initiate rapid synaptic transmission and are regulated primarily by direct interaction with G proteins and SNARE proteins and secondarily by protein phosphorylation. The Cav3 family of alpha1 subunits conduct T-type Ca$^2+$ currents, which are activated and inactivated more rapidly and at more negative membrane potentials than other Ca$^2+$ current types. The distinct structures and patterns of regulation of these three families of Ca$^2+$ channels provide a flexible array of Ca$^2+$ entry pathways in response to changes in membrane potential and a range of possibilities for regulation of Ca$^2+$ entry by second messenger pathways and interacting proteins.
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