Preconditioning limits mitochondrial Ca during ischemia in rat hearts: role of KATP channels

Wang, Lianguo, Gennady Cherednichenko, Lisa Hernandez, Jessica Halow, S. Albert Camacho, Vincent Figueredo, and Saul Schaefer. Preconditioning limits mitochondrial Ca21 during ischemia in rat hearts: role of KATP channels. Am J Physiol Heart Circ Physiol 280: H2321–H2328, 2001.—Prolonged myocardial ischemia results in an increase in intracellular calcium concentration ([Ca]i), which is thought to play a critical role in ischemiareperfusion injury. Ischemic preconditioning (PC) improves myocardial function during ischemia-reperfusion, a process that may involve opening mitochondrial ATP-sensitive potassium (KATP) channels. Because pharmacological limitation of mitochondrial calcium concentration ([Ca]m) overload during ischemia-reperfusion has been shown to improve myocardial function, we hypothesized that PC would reduce [Ca]m during ischemia-reperfusion and that this effect was mediated by opening mitochondrial KATP channels. Isolated rat hearts were subjected to 25 min of global ischemia and 30 min of reperfusion with or without PC in the presence of mitochondrial KATP channel opening (diazoxide, 100 mM) and blockade [5-hydroxydecanoic acid (5-HD), 100 mM]. Contracture during ischemia (end-diastolic pressure) and functional recovery on reperfusion (developed pressure) were assessed. Total [Ca]i and [Ca]m were measured using indo 1 fluorescence. Both PC and diazoxide limited the increase in end-diastolic pressure and resulted in greater functional recovery after 30 min of reperfusion, functional effects that were partially or completely abolished by 5-HD. PC and diazoxide also significantly limited the increase in [Ca]m during ischemia-reperfusion. In addition, PC lowered [Ca]i during reperfusion, whereas diazoxide paradoxically resulted in increased [Ca]i during reperfusion. There was an inverse linear relationship between [Ca]m and developed pressure during reperfusion. PC limits the ischemia-induced increase in mitochondrial, but not total, [Ca]i, an effect mediated by opening mitochondrial KATP channels. These data suggest that the lowering of mitochondrial calcium overload is a mechanism of cardioprotection in PC.