RECONSTITUTION OF THE SKELETAL-MUSCLE DIHYDROPYRIDINE RECEPTOR - FUNCTIONAL INTERACTION AMONG ALPHA(1)-SUBUNIT, BETA-SUBUNIT, GAMMA-SUBUNITAND ALPHA(2)DELTA-SUBUNIT

The L-type voltage-dependent Ca2+ channel purified from skeletal muscl e by virtue of its dihydropyridine (DHP) binding activity, is composed of alpha(1), alpha(2) delta, beta and gamma subunits. The alpha(1) su bunit has the ability to function alone as a Ca2+ channel and a recept or for DHP and other Ca2+ channel antagonists. In this study, the non- alpha(1) components coexpressed with alpha(1) in COS cells were invest igated for their effects on DHP binding and suppression of an anomalou s allosteric regulation of the phenylalkylamine (-)D600 in complexes l acking one or more subunits. (-)D600 increased DHP binding to membrane s of COS cells expressing alpha(1) beta while it did not affect DHP bi nding to skeletal muscle membranes. Coexpression of gamma or alpha(2) delta with alpha(1) beta partially suppressed this effect. Coexpressio n of all the subunits completely eliminated the stimulatory effect of (-)D600, while at the same time increasing the affinity of the complex for DHP to that stabilized in partial complexes by the phenylalkylami ne. These results demonstrate that all of the components that co-purif y are required for the formation of a functional DHP receptor having t he properties of the native skeletal muscle DHP receptor.