Tissue-specific expression of calcium channels.

The high-voltage-activated calcium channel is a multimeric protein complex containing α(1), α(2)/δ, β, and γ subunits. The α(1) subunit is the ion conduction channel and contains the binding sites for calcium channel blockers and toxins. Three genes code for distinct L-type, dihydropyridine-sensitive α(1) subunits; one gene codes for the neuronal P-type (Purkinje) α(1) subunit; and one gene codes for the neuronal N-type α(1) subunit. The smooth and cardiac muscle L-type calcium channel α(1) subunits are splice variants of the same gene. The α(1) subunits are coexpressed with a common α(2)/δ subunit and tissue-specific β subunits (at least three genes). The γ subunit apparently is expressed only in skeletal muscle. The properties of these cloned and expressed calcium channels are discussed here.