Structural characterization of the 1,4-dihydropyridine receptor of the voltage-dependent Ca2+ channel from rabbit skeletal muscle. Evidence for two distinct high molecular weight subunits.

The 1,4-dihydropyridine receptor purified from rabbit skeletal muscle triads was shown to contain four protein components of 175,000, 170,000, 52,000, and 32,000 Da when analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis under nonreducing conditions. Monoclonal antibodies capable of specifically immunoprecipitating the [3H]PN200-110-labeled dihydropyridine receptor from digitonin-solubilized triads recognized the 170,000-Da protein on nitrocellulose transfers of skeletal muscle triads, transverse tubular membranes, and purified dihydropyridine receptor. Wheat germ agglutinin peroxidase stained the 175,000-Da protein on similar nitrocellulose transfers, demonstrating that the 175,000-Da protein is the glycoprotein subunit of the purified dihydropyridine receptor. The apparent molecular weight of the Mr 170,000 protein remained unchanged with reduction, whereas the apparent molecular weight of the glycoprotein subunit shifted from 175,000 to 150,000 upon reduction. These results demonstrate that the 1,4-dihydropyridine receptor of the voltage-dependent Ca2+ channel from rabbit skeletal muscle contains two distinct high molecular weight subunits of 175,000 and 170,000.