ROS and NO trigger early preconditioning:: relationship to mitochondrial KATP channel

Reactive oxygen species (ROS) and nitric oxide (NO) are implicated in induction of ischemic preconditioning. However, the relationship between these oxidant signals and opening of the mitochondrial ATP-dependent potassium (K-ATP) channel during early preconditioning is not fully understood. We observed preconditioning protection by hypoxia, exogenous H2O2, or PKC activator PMA in cardiomyocytes subjected to 1-h ischemia and 3-h reperfusion. Protection was abolished by K-ATP channel blocker 5-hydroxydecanoate (5-HD) in each case, indicating that these triggers must act upstream from the K-ATP channel. Inhibitors of NO synthase abolished protection in preconditioned cells, suggesting that NO is also required for protection. DAF-2 fluorescence (NO sensitive) increased during hypoxic triggering. This was amplified by pinacidil and inhibited by 5-HD, indicating that NO is generated subsequent to K-ATP channel activation. Exogenous NO during the triggering phase conferred protection blocked by 5-HD. Exogenous NO also restored protection abolished by 5-HD or N-omega-nitro-L-arginine methyl ester in preconditioned cells. Antioxidants given during pinacidil or NO triggering abolished protection, confirming that ROS are generated by K-ATP channel activation. Coadministration of H2O2 and NO restored PMA-induced protection in 5-HD-treated cells, indicating that ROS and NO are required downstream from the K-ATP channel. We conclude that ROS can trigger preconditioning by causing activation of the K-ATP channel, which then induces generation of ROS and NO that are both required for preconditioning protection.