Roles of connexin-43 in cardiomyocyte tolerance against ischemic injury

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Myocardial ischemia induced complex formation of gap junction connexin-43 (Cx43) with Src, PKC-ε and p38MAPK-α in rat hearts. Ischemic preconditioning (PC) did not modify Cx34-Src interaction during ischemia but significantly increased binding of Cx43 with PKC-ε. PC suppressed Cx43-p38MAPK binding and p38MAPK activity in the Cx43 immunoprecipitates. Gap junction permeability assessed by Lucifer yellow was significantly suppressed by PC, and this effect of PC was abolished by inhibition of PKC-ε. In contrast, inhibition of p38MAPK modestly increased gap junction permeability during myocardial ischemia. Contribution of suppressed gap junction permeability to myocardial salvage was assessed by activation of the δ-opioid receptor, which is one of receptors responsible for triggering PC mechanisms. A δ-opioid receptor agonist, DADLE, mimicked the effect of PC on gap junction permeability and infarct size, and elimination of its effect on gap junction by a PKC-ε inhibitor attenuated infarct … More size-limiting effect of DADLE by 35%. In cardiomyocyte cell line (H9c2 cell), activation of the δ-opioid receptor, or the IGF receptor induces phosphorylation of Akt and GSK-3β and afford cytoprotection against oxidant stress-induced cell necrosis. Suppression of Cx43 expression by use of its siRNA abolished both PI3K-Akt-GSK-3β signaling and cytoprotection induced by a δ-opioid receptor agonist. However, Akt and GSK-3β phosphorylation and cytoprotection against necrosis by IGF-1 were preserved even after knock-down of Cx43. The results of the present study indicate that Cx43 plays two, at least, important roles as a determinant of myocardial tolerance against ischemia/reperfusion injury. First, gap junction Cx43 is a target of PC mechanisms which suppress propagation of cell injury via the gap junction. PKC-ε and p38MAPKα are a primary inhibitory factor and a counter-acting modulation factor, respectively, of the gap junction regulation by PC. Second, Cx43 plays a crucial role in transmission of cytoprotective PI3K-Akt-GSK-3β signaling from activated G-protein coupled receptors. Less