| Abstract: | The slow inward calcium channel, identified by physiologic and pharmacologic responses and 3H]nitrendipine-specific binding, has been characterized by radiation inactivation and covalent affinity labeling. Target size analysis of guinea pig ileum longitudinal smooth muscle membranes indicates a molecular weight of 278,000 for the calcium channel. An affinity label analog of nifedipine and nitrendipine, 2,6-dimethyl-3,5-dicarbomethoxy-4-(2-isothiocyanatophenyl)-1,4-dihydropyridine, was found to inhibit the calcium channel by a covalent interaction with a protein subunit (Mr = 45,000) of the calcium channel. |
