Degrading process of acute ischemic myocardial cells.

1. Development of acute ischemic myocardial injury was studied in mongrel dogs, induced by ligation of left anterior descending coronary artery (LAD), by biochemical analysis of myocardial fractions such as sarcoplasmic reticulum (SR) and mitochondria (Mt) and by electron microscopic observation of ischemic myocardial cells with lanthanum probe method. 2. Irreversible injury of ischemic myocardium initiated in subendocardial muscle as early as 20 min after occlusion of LAD as expressed degradation of major ATPase protein and phosphatidylcholine and phosphatidylethanolamine of SR and irreversible impairment of state III respiratory and dinitrophenol (DNP)-ATPase activities of Mt, and these necrotic changes advanced to subepicardial layer at about 60 min. 3. Ultrastructural irreversible findings appeared later at about 60 min following inflow of lanthanum ions in ischemia for 30 min. 4. Activation of cathepsin B inside of SR under ischemic acidic metabolism and abnormal inflow of Ca++ into ischemic cardiac myocytes are suspective of very important factors for the initiation of myocardial ischemic injury in early myocardial ischemia.