[Immunoelectron microscopic studies on the localization of creatine kinase M in normal and ischemic myocardial cells]

The localization of creatine kinase M (CK-M) in both normal and acute ischemic canine myocardial cells was studied by immunoelectron microscopy using the anti-CK-M Fab'-horseradish peroxidase conjugate. Myocardial ischemia was induced by occlusion of the left anterior descending coronary artery for 15, 60, or 180 minutes. In the normal myocardial cells, CK-M was localized mostly in the A-band and some in the Z-line, M-line, sarcolemmal membrane, and membrane of sarcoplasmic reticulum. Most CK-M in the A-band appeared to associate with thick fibers. This finding strongly suggests that the CK associated with thick fibers may be the enzyme to rephosphorylate ADP produced by myosin ATPase. In 15 minutes of myocardial ischemia, CK-M showed only minimal changes in its location, i.e., almost similar to normal, indicating that the CK in the A-band still has the ability to couple with myosin ATPase. However, in 60 and 180 minutes of ischemia, the A-band CK dissociated markedly from thick fibers, diffused to the I-band and leaked out to the intercellular spaces. These results suggest that the dissociation and disappearance of the A-band CK from thick fibers induced by progress of myocardial ischemia disrupt the myocardial energy transport system via CK reaction, and lead to the irreversible injury of myocardial cells.