Monoclonal antibody identifies a 200-kDa subunit of the dihydropyridine-sensitive calcium channel

A monoclonal antibody, mAb 1A, that immunoprecipitates the [3H]PN200-110-binding complex from rabbit skeletal muscle has been used to study the subunit structure of the dihydropyridine-sensitive, voltage-activated calcium channel. Digitonin-solubilized [3H]PN200-110-binding component, purified by wheat germ agglutinin chromatography, sediments as a 21 S complex. The sedimentation coefficient of the complex is increased to about 24 S after incubation with mAb 1A IgG. Four polypeptides with apparent molecular weights under nonreducing conditions of 220,000, 200,000, 61,000, and 33,000 co-sediment with the 21 S complex. mAb 1A recognizes the Mr 200,000 polypeptide, as shown by Western blotting analysis. [3H] PN200-110 complex purified by wheat germ agglutinin chromatography followed by immunoaffinity chromatography on an mAb 1A column is comprised primarily of the same four polypeptides. When analyzed by sodium dodecyl sulfate gel electrophoresis under reducing conditions, the Mr 220,000 protein migrates as a polypeptide of Mr 143,000; the mobility of the Mr 200,000 protein recognized by mAb 1A is unaffected by reduction. Thus, the Mr 200,000 polypeptide appears to be a previously undescribed component of the dihydropyridine-binding complex and, in association with the other polypeptides, may comprise the voltage-sensitive calcium channel.