Opening of mitochondrial ATP-sensitive potassium channels enhances cardioplegic protection

Background. Mitochondrial and sarcolemmal ATP-sensitive potassium channels have been implicated in cardioprotection; however, the role of these channels in magnesium-supplemented potassium (K/Mg) cardioplegia during ischemia or reperfusion is unknown. Methods. Rabbit hearts (n = 76) were used for Langendorff perfusion. Sham hearts were perfused for 180 minutes. Global ischemia hearts received 30 minutes of global ischemia and 120 minutes of reperfusion. K/Mg hearts received cardioplegia before ischemia. The role of ATP-sensitive potassium channels in K/Mg cardioprotection during ischemia and reperfusion was investigated, separately using the selective mitochondrial ATP sensitive potassium and channel blocker, 5-hydroxydecanoate, and the selective sarcolemmal ATP-sensitive potassium channel blocker HMR1883. Separate studies were performed using the selective mitochondrial ATP-sensitive potassium channel opener, diazoxide, and the nonselective ATP-sensitive potassium channel opener pinacidil. Results. Infarct size was 1.9% +/- 0.4% in sham, 3.7% +/- 0.5% in K/Mg, and 27.8% +/- 2.4% in global ischemia hearts (p < 0.05 versus K/Mg). Left ventricular peak-developed pressure (percent of equilibrium) at the end of 120 minutes of reperfusion was 91% +/- 6% in sham 92% +/- 2% in K/Mg, and 47% +/- 6% in global ischemia (p < 0.05 versus K/Mg). Blockade of sarcolemmal ATP-sensitive potassium channels in K/Mg hearts had no effect on infarct size or left ventricular peak-developed pressure. However, blockade of mitochondrial ATP-sensitive potassium channels before ischemia significantly increased infarct size to 23% +/- 2% in K/Mg hearts (p < 0.05 versus K/Mg; no statistical significance [NS] as compared to global ischemia) and significantly decreased left ventricular peak-developed pressure to 69% <plus/minus> 4% (p < 0.05 versus K/Mg). Diazoxide when added to K/Mg cardioplegia significantly decreased infarct size to 1.5% <plus/minus> 0.4% (p < 0.05 versus K/Mg). Conclusions. The cardioprotection afforded by K/Mg cardioplegia is modulated by mitochondrial ATP-sensitive potassium channels. Diazoxide when added to K/Mg cardioplegia significantly reduces infarct size, suggesting that the opening of mitochondrial ATP-sensitive potassium channels with K/Mg cardioplegic protection would allow for enhanced myocardial protection in cardiac operations. (C) 2001 by The Society of Thoracic Surgeons.