calcium channel, a slow voltage-gated channel very permeable to calcium ions and slightly permeable to sodium ions, existing in three subtypes designated L, M, and N and located throughout the body. In excitable cells the action potential results from the transmembrane fluxes of Na+, Ca2+, and K+. Calcium channels are the main cause of action potentials in certain smooth muscles, and the N channels regulate neurotransmitter release. Also called calcium-sodium channel.
