45Ca2+ uptake in rat brain neurons: absence of sensitivity to the Ca2+ channel ligands nitrendipine and Bay K 8644

Abstract

K+-stimulated 45Ca2+ uptake into intact rat brain cells was biphasic, consisting of a fast first phase and a slow second phase; the latter was Na+ dependent. Cobalt and cadmium at 10-4 and 10-3 M produced 19-97% block of first phase 45Ca2+ uptake, but nitrendipine (to 10-6 M) and Bay K 8644 (to 10-6 M) were without effect on uptake and were similarly without effect in cells prepared in the presence of ATP, cAMP, Mg2+, and protease inhibitors. The second of K+-stimulated 45Ca2+ uptake was inhibited by 3,4-dichlorobenzamil (IC50, 29.6 .mu.M). Depolarization-induced 45Ca2+ uptake into intact rat brain cells occurs by at least two different mechanisms. The first phase probably represents uptake through 1,4-dihydropyridine-insensitive Ca2+ channels, while the second phase is probably due to Na+-Ca2+ exchange.