Tissue-specific expression of calcium channels.

The high-voltage-activated calcium channel is a multimeric protein complex containing alpha1, alpha2/delta, beta, and gamma subunits. The alpha1 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 alpha1, subunits; one gene codes for the neuronal P-type (Purkinje) alpha1 subunits; and one gene codes for the neuronal N-type alpha1 subunit. The smooth and cardiac muscle L-type calcium channel alpha1 subunits are splice variants of the same gene. The alpha1 subunits are coexpressed with a common alpha2/delta subunit and tissue-specific beta subunits (at least three genes). The gamma subunit apparently is expressed only in skeletal muscle. The properties of these cloned and expressed calcium channels are discussed here.