Oxygen Consumption and Mitochondrial Membrane Potential in Postischemic Myocardium

Abstract

Oxygen consumption may be disproportionately high relative to contractile function in postischemic reperfused myocardium. The study reported in this chapter investigated the mechanism of the dissociation between oxygen consumption and contractile function in postischemic reperfused myocardium using isolated rat hearts. Mitochondrial dysfunction secondary to increased calcium uptake has been implicated as an important mediator of reperfusion injury in the heart. In postischemic, isovolumic, antegrate-perfused rat hearts, the myocardial oxygen consumption rate (MVO2) and contractile function were studied in relation to mitochondrial function. Left ventricular pressure, coronary blood flow, and oxygen consumption were determined. Mitochondrial respiration and the mitochondrial membrane potential were measured by polarography and flow cytometry, respectively. To examine the role of mitochondrial calcium uptake in ischemia reperfusion injury, isolated rat hearts perfused with ruthenium red, which inhibits calcium uptake by mitochondria, were compared to control perfused hearts. After stabilization, hearts were subjected to 60 minutes of no-flow ischemia, followed by 60 minutes of reperfusion. At 15 minutes after the onset of reperfusion, there was poor recovery of left ventricular developed pressure to 64% of the control level, but myocardial oxygen consumption was increased to 134% of control. The addition of 2.5 μM ruthenium red to the perfusate resulted in a decrease of myocardial oxygen consumption. The oxygen consumption rate in state 3 of mitochondria decreased similarly following reperfusion in control and ruthenium red hearts. The mitochondrial membrane potential was reduced to 89% (logarithmic scale) after 15 minutes of reperfusion and then returned to preischemic level. These data suggest that the dissociation between oxygen consumption and contractile function following early reperfusion is partly caused by the repair of intracellular damage resulting from calcium accumulation to mitochondria.