1. Alterations in the localization and the intensity of acid phosphatase activity were studied electron microscopically in acute ischemic myocardial cells in the dog, in relation to processes of cellular degradation.
2. In normal myocardial cells, the acid phosphatase activity was concentrated in the terminal cisternae, the longitudinal elements and the subsarcolemmal cisternae of the sarcoplasmic reticulum and the primary lysosomes. Activity was moderate in the secondary lysosomes, residual bodies and Golgi apparatus.
3. As early as 15min after coronary ligation the intensity of acid phosphatase activity increased in the enlarged lysosomes and the sarcoplasmic reticulum of the ischemic myocardial cells. Fine deposits of the reaction product were distributed in the sarcoplasm around lysosomes and the sarcoplasmic reticulum after 30min, and the activity began to decrease in lysosomes and in the sarcoplasmic reticulum. One to 3 hours after ligation, intramitochondrial dense deposits appeared, and the reaction product decreased both in lysosomes and the sarcoplasmic reticulum. The fine reaction product, which leaked from lysosomes and the sarcoplasmic reticulum, was scattered in the sarcoplasm and was accompanied by fine structural changes indicating cellular necrosis.
4. From these findings it is strongly suggested that acid hydrolases in lysosomes and the sarcoplasmic reticulum are closely related to the necrotic process in ischemic myocardial cells.