Calcium channels are found in all excitable membranes, where they provide a link between membrane changes and cellular responses that are controlled by cytosolic Ca 2+ . Channel opening is activated by depolarization and modulated by changes in [Ca 2+ ] 1 , by hormones and neural transmitters, and by phosphorylation. Ca-channels appear to select for Ca 2+ over monovalent cations such as Na + and K + by momentarily binding Ca 2+ as it permeates. Certain divalent cations, like Cd 2+ , block channels, as do organic Ca-antagonists like verapamil, which however act at a different site within the channel. Dihydropyridine drugs act as modifiers of channel gating. Though a number of Ca-channel types have been identified, all are probably glycoproteins. In skeletal muscle, the molecular weight is 240 kD, apparently composed of three sub-units, one of which may be phosphorylated in a regulatory way.
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Peter Stanfield (1986) studied this question.