Effect of calcium on Na-K-ATPase activity in depolarized rat cortical synaptosomes as determined on the basis of oxygen consumption

Summary The oxygen consumption of rat cortical synaptosomes together with its ouabain-sensitive component were measured after veratrine-induced depolarization in the presence and in the absence of calcium, and with calcium added after depolarization by veratrine or potassium. Taking the ouabainsensitive component of oxygen consumption as an indicator of Na-K-ATPase activity it was concluded that calcium entry during depolarization decreased synaptosomal Na-K-ATPase activity only slightly and in a protracted manner. Consequently, Ca⁺⁺-induced inhibition of Na-K-ATPase does not seem to serve as a trigger mechanism of transmitter release.