Time-dependent changes in canine cardiac mitochondrial function and ultrastructure resulting from coronary occlusion...

Time-dependent changes in mitochondrial function and structure resulting from 1 hr of left circumflex coronary artery occlusion followed by 2 to 24 hr of reperfusion were examined. These changes were correlated with changes in myocardial ultrastructure, tissue water content, infarct size and mitochondrial calcium content. The heart was removed after different periods of reperfusion, and mitochondria were isolated from ischemic and nonischemic regions of the left ventricle. Tissue samples from ischemic and nonischemic myocardium also were taken for electron microscopy and tissue water content determinations. Infarct size was measured by the nitroblue tetrazolium staining method. Oxygen consumption by mitochondria isolated from ischemic and nonischemic myocardium was measured in vitro. Mitochondria from ischemic myocardium showed time-dependent decreases in rates of oxygen consumption and tightness of coupling. Electron microscopy revealed progressive ultrastructural deterioration in ischemic myocardium, including accumulation of calcium deposits within mitochondria, a finding corroborated by elevated concentrations of calcium in mitochondria isolated from the same area. Tissue wet-to-dry weight ratios were increased significantly in ischemic myocardium. A small, but significant, decrease in respiratory function was observed in mitochondria isolated from nonischemic myocardium several hrs after reperfusion; however, normal respiration was observed 24 hrs after release of occlusion. This latter observation indicates that the nonischemic zone also is affected by regional ischemia. The results obtained indicate that temporary left circumflex artery occlusion and reperfusion result in progressively decreasing mitochondrial function and structure within the ischemic myocardium, and that these changes are accompanied by cellular electrolyte alterations.