Changes in cardiac ultrastructure and myofibrillar proteins during ischemia in dogs, with special reference to changes in Z lines.

This study was designed to examine whether or not coronary ligation produces changes in myofibrillar proteins, especially Z line proteins including alpha-actinin and the 55 kDa protein, in the dog. Changes in ultrastructure of the myocardium after coronary ligation were also studied. A branch of the left anterior descending coronary artery was ligated for a period of 3, 6, 24 or 72 h. Coronary ligation produced ultrastructural changes in Z lines (characterized by broader and wavy Z lines) as well as changes in glycogen granules, mitochondria, and nuclei. Myofibrils were isolated from the myocardium that had been made ischemic by coronary ligation. The yield of myofibrils was reduced as the ischemic period was increased. Phase microscopic examination of the isolated myofibrils from the ischemic myocardium revealed that there were spread Z lines with wider I bands, these changes being essentially the same as those observed by the electron microscope in the ischemic myocardium. The effect of coronary ligation on the myofibrillar proteins was studied by means of polyacrylamide gel electrophoresis. In the isolated myofibrils from the myocardium 3 h after coronary ligation, there were decreases in the percentage of actin, alpha-actinin and the 55 kDa protein, and these changes progressively increased with lengthening of the ischemic period. These results suggest that coronary ligation decreases actin, alpha-actinin and the 55 kDa protein, in association with ultrastructural changes of the Z lines.