Roles of phospho-GSK-3β in myocardial protection afforded by activation of the mitochondrial KATP channel

The aim of this study was to determine the roles of glycogen synthase kinase-3 beta (GSK-3 beta) in cardioprotection by activation of the mitochondrial ATP-sensitive K(+)channel (mK(ATp) channel). In isolated rat hearts, an mK(ATp) activator, diazoxide, and a GSK-3 beta inhibitor, SB216763, similarly limited infarct size and the combination of these agents did not afford further protection. The protection by pre-ischernic treatment with diazoxide was abolished by inhibition of protein kinase C-epsilon (PKC-epsilon) or phosphatidylinositol-3-kinase (PI3K) upon reperfusion. Infusion of a GSK-3 beta inhibitor ( LiCl), but not diazoxide, during reperfusion limited infarct size. Inhibition of PKC-epsilon or PI3K did not affect the protection by LiCl. Diazoxide infusion alone did not induce GSK-3 beta phosphorylation. However, diazoxide infusion before ischemia increased mitochondrial phospho-GSK-3 beta level and reduced cyclophilin-D (CypD) binding to adenine nucleotide translocase (ANT) at 10 min after reperfusion. This diazoxide-induced GSK-3 beta phosphorylation was inhibited by blockade of the mK(ATP) channel before ischemia and by blockade of PKC-epsilon, PI3K or the adenosine A2b receptor at the time of reperfusion. Inhibition of GSK-3 beta by LiCl during reperfusion increased phospho-GSK-3 beta but had no significant effect on CypD-ANT binding. These results suggest that GSK-3 beta phosphorylation at the time of reperfusion by a PKC-epsilon, PI3K- and A2b receptor-dependent mechanism contributes to prevention of myocardial necrosis by pre-ischemic activation of the mK(ATP) channel. Inhibition of CypD-ANT interaction may contribute to mK(ATP)-induced myocardial protection, though it is not the sole mechanism of phospho-GSK-3 beta-mediated cytoprotection. (C) 2010 Elsevier Ltd. All rights reserved.