Dihydropyridine‐sensitive Ca2+channel in aneurally cultured human muscles Relationship between high‐affinity binding site and inhibition of calcium uptake

Dihydropyridine‐sensitive Ca2+channels and the relationship between binding of dihydropyridine derivatives and depolarization‐induced Ca2+uptake have been studied in aneurally cultured human muscle. Analysis of the equilibrium binding of the 1,4‐dihydropyridine derivative (+)‐PN200‐110 revealed a single high‐affinity binding site with a Kdof 0.15±0.05 nM and a Bmaxof 87±12 fmol/mg protein. Inhibition of (+)‐[3H]PN200‐110 binding by nitrendipine revealed a Kiof 0.8 nM for the nitrendipine‐receptor complex. Depolarization of cultured human muscle achieved by elevating the K+concentration increased the uptake 45Ca2+which was inhibited by nitrendipine with an IC50of 1.1 nM. This study demonstrates that aneurally cultured human muscle has dihydropyridine‐sensitive voltage‐dependent Ca2+channels which are functional when the fibers are depolarized.