Exhaustion of calcium does not terminate evoked neurotransmitter release

Theories are considered which assume that termination of evoked release is caused by the exhaustion of intracellular Ca. It is shown that such theories predict, contrary to experiment, that total release is an unsaturated function of intracellular Ca whose duration depends strongly on extracellular Ca. These and other findings lead to the conclusion that termination must be due to the fast change of another parameter (not intracellular Ca).