⁴⁵Ca²⁺ Uptake into Rat Whole Brain Synaptosomes Unaltered by Dihydropyridine Calcium Antagonists

Voltage-dependent 45Ca2+ uptake into rat whole brain synaptosomes was measured after 3-s KCl-induced depolarization to investigate possible inhibitory effects of calcium antagonists, nitrendipine, nimodipine, and nisoldipine. At a Ca2+ concentration of 1.2 mM, nitrendipine, in concentrations ranging from 0.1 nM to 10 microM, had no effect on 45Ca2+ uptake. When the Ca2+ concentration was lowered to 0.06 and 0.12 mM, nitrendipine, 10 microM, inhibited 45Ca2+ uptake in response to 109 mM KCl depolarization. However, in a separate concentration response study, nitrendipine, nimodipine, and nisoldipine, 0.1 nM to 10 microM, failed to alter the uptake of 45Ca2+ (0.06 mM Ca2+) into 30 mM KCl-depolarized synaptosomes. The high concentrations of these agents required to depress 45Ca2+ uptake indicate that the dihydropyridine calcium antagonists are considerably less potent in brain tissue than in peripheral tissue.