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

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 phase of K⁺-stimulated ⁴⁵Ca²⁺ uptake was inhibited by 3,4-dichlorobenzamil (IG₅₀, 29.6 μM). 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.