A new method for cytochemical demonstration of calcium in heart muscle.

The ortho-cresolphtalein complex was successfully adapted for the electron microscopic cytochemical demonstration of calcium. The reaction product is of granular nature with sufficient electron density for finer localization. Intense precipitation was found on the sarcolemma and transverse tubules and in the sarcoplasmic reticulum. Myofilaments, mitochondria and capillary endothelial cells also showed a positive reaction. The electron microprobe analysis of the precipitate proved the presence of calcium. Disturbing effects of magnesium ions were prevented by the incorporation of 8-hydroxyquinoline in the incubation medium.