Cytochemical methods of detecting the ultrastructural localization of calcium

Conditions and potentialities of electron-cytochemical techniques for calcium detection are analysed in terms of current evidence on the role of membranes in sequestration of intracellular calcium pools. In most cases these conditions did not allow to preserve a native localization of calcium because the lability of calcium pools enclosed within membranes and the action of electron microscopic fixatives on the membrane permeability to Ca2+ and Ca-precipitating agents were not taken into account. Considering these factors it is essential that both the fixator and Ca-precipitating agent could diffuse through membranes simultaneously. The modes to ensure this essential condition as well as the reasons and ways to avoid artifacts in cytochemical studies are given.