32,000-Dalton Subunit of the 1,4-Dihydropyridine Receptor

Polyclonal antibodies to the 32,000-Da polypeptide of the 1,4-dihydropyridine receptor of the voltage-dependent Ca2+ channel have been produced and used to characterize the association of the 32,000-Da polypeptide (gamma subunit) with other subunits of the dihydropyridine receptor. The 32,000-Da polypeptide was found to copurify with alpha 1 and alpha 2 subunits at each step of the purification of the dihydropyridine receptor. Monoclonal antibodies against the alpha 1 and beta subunits immunoprecipitate the digitonin-solubilized dihydropyridine receptor as a multisubunit complex that includes the 32,000-Da polypeptide. Polyclonal antibodies generated against both the nonreduced and reduced forms of the alpha 2 subunit and the gamma subunit have been used to show that the 32,000-Da polypeptide is not a proteolytic fragment of a larger component of the dihydropyridine receptor and not disulfide linked to the alpha 2 subunit. Our results demonstrate that the 32,000-Da polypeptide (gamma subunit) is an integral and distinct component of the dihydropyridine receptor.