Undiminished mitochondrial function during stunning in rabbit heart at 288C

Objective: To investigate effect of brief ischemia on mitochondrial function in intact myocardium, rather than in isolated .mitochondria. Methods: The mitochondrial response was characterized by the mean response time t of cardiac mitochondrial Omito 2 consumption to steps in heart rate. Isolated isovolumic rabbit hearts were perfused at 288C with a constant flow of Tyrode solution containing 11 mM glucose. O consumption and t were determined before ischemia and after 25 min of no-flow global ischemia2 mito . . .during which hearts were either paced IqP, ns8 or unpaced IyP, ns8. A non-ischemic control group ns8 was also examined. . Results: At 20 min reperfusion, developed left ventricular pressure DLVP after IqP was decreased to 47"3 % mean"s.e.m.;.P-0.05 of control DLVP without significant changes in venous creatine kinase efflux, indicating contractile stunning. In contrast, complete contractile recovery was observed after IyP. Before ischemia, t was 11.2"0.6 and 14.9"0.7 s for heart rate steps frommito . 60 to 70 and from 60 to 120 beatsrmin, respectively. The t was lower P-0.05 for the corresponding downward steps 10.5"0.6mito. . .and 12.4"0.6 s, respectively. An increase P-0.05 in t was observed in the course of the experiment for upward 1.2"0.3 s andmito . downward steps 1.4"0.3 s, but the change was similar after ischemia to that in time-matched controls P)0.05, both for IyP and.IqP vs. control. Oxygen consumption, compared at fixed levels of the rate=pressure product, was unchanged after ischemia .P)0.05, for both IyP and IqP vs. controls, suggesting undiminished efficiency of mitochondrial ATP production. Conclusions: Twenty-five minutes ischemia does not affect mitochondrial function in rabbit hearts at 288C, even when contractile stunning resulted