Binding of [³H]nimodipine to cardiac and smooth muscle membranes

Specific binding of [³H]nimodipine to membranes from rat ventricle and guinea pig ileal longitudinal smooth muscle was studied. Dissociation constants were 0.24 and 0.12 nM, and the maximal number of binding sites were 0.4 and 0.75 pmol/mg protein for cardiac and smooth muscle, respectively. The values obtained for both types of muscle were similar to those obtained for [³H]nitredipine binding, as were the potencies of a series of dihydropyridines for competing with [³H]nimodipine. These results support the hypothesis that the binding site characterized is that mediating the pharmacological effects of these compounds.