Effect of pressure overload on cardioprotection of mitochondrial K _ATP channels and GSK-3β: Interaction with the MPT pore

Background: The mitochondrial permeability transition (MPT) pore may serve as the end-effector of cardioprotective mechanisms, namely the mitochondrial K_ATP channels and glycogen synthase kinase-3β (GSK-3β). We recently showed that augmented MPT pore induction contributes to pressure overload-induced exacerbation of infarct size. This study tests the hypotheses that (i) elevation in perfusion pressure attenuates cardioprotection associated with activation of mitochondrial K_ATP channels or inhibition of GSK-3β and (ii) perfusion pressure modulates the regulation of the MPT pore by mitochondrial K_ATP channels and/or GSK-3β. Methods: Langendorff-perfused hearts were subjected to a regional ischemia-reperfusion insult at a perfusion pressure of either 80 or 160 cm H₂O. The perfusion medium contained no drug, diazoxide (80 μmol/l; mitochondrial K_ATP channel opener), lithium chloride (LiCl, 1 mmol/l; nonselective inhibitor of GSK-3β), SB-216763 (3 μmol/l; selective inhibitor of GSK-3β), cyclosporine A (0.2 μmol/l; inhibitor of MPT pore induction), glibenclamide (50 μmol/l; inhibitor of K_ATP channels), and the combination of cyclosporine A and glibenclamide or the combination of glibenclamide and LiCl. Results: The increase in perfusion pressure in the absence of a drug caused larger infarcts, an effect associated with poorer recovery of function following ischemia reperfusion. Treatment with either diazoxide or cyclosporine A reduced infarct size at both perfusion pressures but in contrast to diazoxide, cyclosporine A was more protective at the higher pressure. On the other hand, LiCl and SB-216763 reduced infarct size at both pressures, with the effect more marked at the higher perfusion pressure. Glibenclamide did not affect infarct size but eliminated the cardioprotective effect of cyclosporine A while having no effect on LiCl-induced cardioprotection. Conclusion: Perfusion pressure primarily affects GSK-3β-mediated regulation of MPT pore formation in the ischemic reperfused heart.