Abstract
1. Ultrastructural histochemical distribution and intensity of adenylate cyclase (ACLase) activity were studied in the normal myocardial cells of the dog utilizing adenylylimidodiphosphate (AMP-PNP) as a substrate and their alterations in acute ischemia were examined in correlation with the ischemic fine structural changes. 2. In the normal myocardial cell, the electron dense reaction precipitate of ACLase activity was intensely found in the terminal cisternae, subsarcolemmal cisternae of the sarcoplasmic reticulum (SR) and moderately longitudinal tubules of SR, along the gap junction of the intercalated disc and sarcolemmal membrane. 3. In the ischemic myocardial cells, the reaction precipitate was transiently increased at 15 to 30 min after coronary occlusion and then decreased after 60 min in SR, together with the ischemic substructural changes such as loss of glycogen granules, the appearance of dense deposits in mitochondria, etc. After 3 to 12 hours, ACLase activity was faint or disappeared with the increasing ischemic ultrastructural changes. 4. Activation of ACLase activity in the early stage of myocardial ischemia is conceivable to be due to tissue reaction such as release of catecholamine from the ischemic myocardium and a comformational change in ACLase molecule in the ischemic state and its decrease from 60 min to 3 hours to the degradation of ACLase itself in the degenerative process of ischemic myocardial cells.
