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 Kd of 0.15 +/- 0.05 nM and a Bmax of 87 +/- 12 fmol/mg protein. Inhibition of (+)-[3H]PN200-110 binding by nitrendipine revealed a Ki of 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 IC50 of 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.