Diazoxide-induced cardioprotection requires signaling through a redox-sensitive mechanism

Diazoxide, a selective opener of the mitochondrial ATP-sensitive potassium channel, has been shown to elicit tolerance to ischemia in cardiac myocytes and in perfused heart. However, the mechanism of this cardioprotection is poorly understood. Because reactive oxygen species (ROS) are recognized as important intracellular signaling molecules and have been implicated in isc hemic preconditioning, we examined diazoxide-induced ROS production in adul t cardiomyocytes, Cells treated with 50 mu mol/L diazoxide showed a 173% in crease in ROS production relative to baseline. 5-Hydroxydecanoate was found to attenuate the diazoxide-induced increase in ROS generation. The diazoxi de-induced increase in ROS also was abrogated by the addition of either the antioxidant N-acetylcysteine (NAC) or N-mercaptopropionylglycine. We also examined the ability of NAC to block the protective effects of diazoxide in the perfused rat heart. After 20 minutes of global ischemia and 20 minutes of reflow, hearts perfused with 100 mu mol/L diazoxide before ischemia sho wed significantly improved postischemic contractile function relative to un treated hearts (84% versus 29% of initial left ventricular developed pressu re, respectively). Hearts treated with diazoxide in the presence of 4 mmol/ L NAC recovered 53% of initial left ventricular developed pressure, whereas hearts treated with NAC alone recovered 46% of preischemic function. Using P-31 NMR spectroscopy, we found that, similar to preconditioning, diazoxid e significantly attenuated ischemia-induced intracellular acidification and enhanced postischemic recovery of phosphocreatine levels, both of which we re blocked by cotreatment with NAG. These data suggest that the cardioprote ctive actions of diazoxide are mediated by generation of a pro-oxidant envi ronment.