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 K(ATP) channel activation has not been elucidated. It has been suggested that activation of mitochondrial K(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 μM). Different Ca²⁺ concentrations (0 to 5 x 10^-7 M) were used to simulate the effect of Ca²⁺ overload; state 2, mito 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/Δt); 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/Δt. PINACIDIL improved state 3, ADP/Δt, 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 mito, protecting mito 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 mito from Ca²⁺ overload. (C) 2000 Academic Press.