Opening of potassium channels protects mitochondrial function from calcium overload

Ischemic preconditioning (IPC) protects myocardium from ischemia reperfusion injury by activating mitochondrial K-ATP channels. However, the mechanism underlying the protective effect of R-ATP channel activation has not been elucidated. It has been suggested that activation of mitochondrial R-ATP channels may prevent mitochondrial dysfunction associated with Ca2+ overload during reperfusion. The purpose of this experiment was to study, in an isolated mitochondrial preparation, the effects of mitochondrial K-ATP channel opening on mitochondrial function and to determine whether it protects mitochondria form Ca2+ overload. Mitochondria (mito) were isolated from rat hearts by differential centrifugation (n = 5/group). Mito respiratory function was measured by polarography without (CONTROL) or with a potassium channel opener (PINACIDIL, 100 muM). Different Ca2+ concentrations (0 to 5 x 10(-7) M) were used to simulate the effect of Ca2+ overload; state 2, mite oxygen consumption with substrate only; state 3, oxygen consumption stimulated by ADP; state 4, oxygen consumption after cessation of ADP phosphorylation; respiratory control index (RCI: ratio of state 3 to state 4); rate of oxidative phosphorylation (ADP/Deltat); and ADP:O ratio were measured. PINACIDIL increased state 2 respiration and decreased RCI compared to CONTROL. Low Ca2+ concentrations stimulated state 2 and state 4 respiration and decreased RCI and ADP:O ratios. High Ca2+ concentrations increased state 2 and state 4 respiration and further decreased RCI, state 3, and ADP/Deltat. PINACIDIL improved state 3, ADP/Deltat and RCI at high Ca2+ concentrations compared to CONTROL. Pinacidil depolarized inner mitochondrial membrane, as evidenced by decreased RCI and increased state 2 at baseline. Depolarization may decrease Ca2+ influx into mite, protecting mite from Ca2+ overload, as evidenced by improved state 3 and RCI at high Ca2+ concentrations. The myocardial protective effects resulting from activating K-ATP channels either pharmacologically or by IPC may be the result of protecting mite from Ca2+ overload. (C) 2000 Academic Press.