The role of phospholipase in mitochondrial dysfunction after coronary reperfusion in the canine myocardium

The left anterior descending coronary artery of a dog was occluded for 15 min followed by a 5 min reperfusion in order to investigate the mechanism responsible for the paradoxical exacerbation of heart mitochondrial dysfunction caused by reperfusion. The mitochondrial function was assessed and the concentration of Ca++, phospholipids and free fatty acids (FFA) were determined. The relative importance of mitochondrial lysophospholipids was also investigated. Eleven dogs (30.6%) developed "reperfusion arrhythmia" (arrhythmia group) but 25 did not (control group). Although mitochondrial dysfunction was observed in the reperfused area even in the control group, a greater impairment of mitochondrial function was observed in the reperfused area in the arrhythmia group. There was no significant difference in the contents of FFA and phospholipids in the mitochondria from the normal area of both groups and from the reperfused area of the control group. However, a marked increase in eight FFA and a significant decrease in phospholipids were observed in the mitochondria from the reperfused area of the arrhythmia group. A significant increase in Ca++ content both in the myocardium and the mitochondria from the reperfused area was observed in the arrhythmia group but not in the control group. In separate experiments, the mitochondria prepared from dog left ventricle were incubated with either phospholipase C (PhC) or phospholipase A2 ( PhA2 ). Both phospholipases induced severe mitochondrial dysfunction. PhC induced a significant increase in FFA, quite analogous to the changes in mitochondrial FFA caused by reperfusion in vivo. PhA2 also induced a tremendous increase in FFA but only in the content of unsaturated FFA. Although PhC did not affect the lysophospholipid profiles, PhA2 induced lysophosphatidyl choline. These results indicate that mitochondrial damages characteristic of the early phase of coronary reperfusion may be caused by the action of PhC, activated by increased intracellular Ca++, which in turn induces degradation of the mitochondrial membrane.