Infarct size limitation by nicorandil: Roles of mitochondrial KATP channels, sarcolemmal KATP channels, and protein kinase C

Objectives This study aimed to examine: 1) whether nicorandil protects the ischemic myocardium by activating sarcolemmal adenosine triphosphate (ATP)-sensitive K+ (sarcKATP) channels or the mitochondrial KATP (mitoKATP) channels, and 2) whether protein kinase C (PKC) activity is necessary for cardioprotection afforded by nicorandil. Background Nicorandil is a hybrid of nitrate and a KATP channel opener that activates the sarcKATP and mitoKATP channels. Both of these KATP channels are regulated by PKC, and this kinase may be activated by nitric oxide and also by oxygen free radicals (OFR) generated after mitoKATP channel opening. Methods In isolated rabbit hearts, infarction was induced by 30-min global ischemia/2-h reperfusion with monitoring of the activation recovery interval (ARI), an index of action potential duration. Protein kinase C translocation was assessed by Western blotting. Results Nicorandil did not change ARI before ischemia, but it accelerated ARI shortening after the onset of ischemia and reduced infarct size by 90%. A sarcKATP channel selective blocker, HMR1098, abolished acceleration of ischemia-induced ARI-shortening by nicorandil and eliminated 40% of nicorandil-induced infarct size limitation. A mitoKATP channel selective blocker, 5-hydroxydecanoate, abolished the protection afforded by nicorandil without affecting ARI. Cardioprotection by nicorandil was inhibited neither by an OFR scavenger, N-2-mercaptopropionylglycine nor by a PKC inhibitor, calphostin C, at a dose that was capable of inhibiting PKC-ε translocation after preconditioning. Conclusions Both the sarcKATP and mitoKATP channels are involved in anti-infarct tolerance afforded by nicorandil, but PKC activation induced by nitric oxide or OFR generation, if any, does not play a crucial role.