[3H]nimodipine specific binding to cardiac myocytes and subcellular fractions

[3H]Nimodipine binding was studied in isolated myocytes from rat heart and in partially purified sarcolemma, sarcoplasmic reticulum and mitochondrial fractions from dog heart. In isolated myocytes, the density of [3H]nimodipine specific sites (10(6) per cell) was close to density of [3H]QNB sites (0.8 x 10(6) per cell) and higher than that of [3H]DHA sites (0.2 x 10(6) per cell). During subcellular fractionation, [3H]nimodipine binding did not copurify with plasma membrane markers. The highest densities were found in fractions enriched in sarcolemma or in sarcoplasmic reticulum. No specific binding was found in mitochondria. These results indicate that the localization of [3H]nimodipine sites is not restricted to areas of the plasma membrane rich in beta-adrenoceptors, muscarinic receptors and sodium pump sites.