Putative Ca2+ channels in cardiac membranes. Subcellular distribution of [3H]nitrendipine receptors

The binding of Ca2+ channel blocking drug nitrendipine was studied in purified sarcolemma (SL), fragmented sarcoplasmic reticulum (SR), and crude membranes isolated from porcine left ventricle. The density of specific [3H]nitrendipine binding sites was compared to Na+/Ca2+ exchange and (Na+, K+)ATPase activities of each membrane preparation. Enrichment of [3H]nitrendipine binding sites in purified SL correlates excellently with the purification of the two studied sarcolemmal marker activities. The results suggest that high affinity nitrendipine receptors are solely localized in cardiac SL.