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

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 ouabain-sensitive 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.