Received for publication January 17, 2006.
Revised April 7, 2006.
Accepted for publication April 10, 2006.

IB-MECA confers cardioprotection at reperfusion by inhibiting mitochondrial permeability transition pore opening via glycogen synthase kinase 3

Abstract

While the adenosine A₃ receptor agonist N⁶-(3-iodobenzyl)-adenosine-5'-N-methylcarboxamide (IB-MECA) has been reported to be cardioprotective at reperfusion, little is known about the mechanisms underlying the protection. We hypothesized that IB-MECA may protect the heart at reperfusion by preventing the opening of mitochondrial permeability transition pore (mPTP) through inactivation of glycogen synthase kinase 3 (GSK-3). IB-MECA (1 µM) applied during reperfusion reduced infarct size in isolated rat hearts, an effect that was abrogated by the selective A₃ receptor antagonist MRS1334 (100 nM). The effect of IB-MECA was abrogated by the mPTP opener atractyloside (20 µM), implying that the action of IB-MECA may be mediated by inhibition of the mPTP opening. In cardiomyocytes, IB-MECA attenuated oxidant-induced loss of mitochondrial membrane potential (_m), which was reversed by MRS1334. IB-MECA also reduced Ca²⁺-induced mitochondrial swelling. IB-MECA enhanced phosphorylation of GSK-3 (Ser⁹) upon reperfusion, and the GSK-3 inhibitor SB216763 (3 µM) mimicked the protective effect of IB-MECA by attenuating both infarction and the loss of _m. In addition, the effect of IB-MECA on GSK-3 was reversed by wortmannin (100 nM), and IB-MECA was shown to enhance Akt phosphorylation upon reperfusion. In contrast, rapamycin (2 nM) failed to affect GSK-3 phosphorylation by IB-MECA and IB-MECA did not alter phosphorylation of either mTOR (Ser²⁴⁴⁸) or p70s6K (Thr³⁸⁹). Taken together, these data suggest that IB-MECA prevents myocardial reperfusion injury by inhibiting the mPTP opening through the inactivation of GSK-3 at reperfusion. IB-MECA-induced GSK-3 inhibition is mediated by the PI3-kinase/Akt signal pathway but not by the mTOR/p70s6K pathway.

Key words: Adenosine A3 receptors, GSK-3, mPTP, oxidant stress, reperfusion injury, signal transduction

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