CLONING AND EXPRESSION OF A CARDIAC BRAIN BETA-SUBUNIT OF THE L-TYPE CALCIUM-CHANNEL

The skeletal muscle dihydropyridine receptor/Ca2+ channel is composed of five protein components (alpha-1, alpha-2-delta, beta, and gamma). Only two such components, alpha-1 and alpha-2, have been identified in heart. The present study reports the cloning and expression of a novel beta-gene that is expressed in heart, lung, and brain. Coexpression of this beta with a cardiac alpha-1 in Xenopus oocytes causes the following changes in Ca2+ channel activity: it increases peak currents, accelerates activation kinetics, and shifts the current-voltage relationship toward more hyperpolarized potentials. It also increases dihydropyridine binding to alpha-1 in COS cells. These results indicate that the cardiac L-type Ca2+ channel has a similar subunit structure as in skeletal muscle, and provides evidence for the modulatory role of the beta-subunit.