Postconditioning inhibits mPTP opening independent of oxidative phosphorylation and membrane potential

Mitochondrial permeability transition pore (mPTP) inhibition plays a relevant role in postconditioning (PostC). Ischemia damages the electron transport chain, and the potential contribution of additional modifications in mitochondrial function caused by PostC remains unknown. We sought to determine which mitochondrial functions are involved in the inhibition of mPTP opening during the first minutes of reperfusion. Anesthetized New Zealand White rabbits underwent 30-min ischemia followed by 10-min reperfusion. At reperfusion, they received either no intervention (Control, C), PostC with 4 cycles of 1-min ischemia followed by 1-min reperfusion, or an IV injection of 5 mg/kg cyclosporine A (CsA: a powerful inhibitor of mPTP opening). Sham rabbits underwent no ischemia throughout the 40-min experiment. At the end of the 10-min reperfusion, mitochondria were isolated from the area at risk by differential centrifugations. Calcium retention capacity (CRC) and mitochondrial membrane potential (Delta Psi(m)) were assessed by fluorimetry in subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria. Oxidative phosphorylation was assessed using a Clark-type electrode, and oxidative stress via protein carbonylation by Western blotting. PostC and CsA treatments improved CRC when compared to the C group. Control, PostC and CsA mitochondria exhibited a comparable significant dissipation of Delta Psi(m), together with a comparable significant decrease in state 3 and an increase in state 4 respiration, in both SSM and IFM. However, PostC but not CsA treatment reduced total heart oxidative stress. These data suggest that during the early minutes of reperfusion, PostC reduces oxidative stress and inhibits mPTP opening, independent of alteration of oxidative phosphorylation or of Delta Psi(m). (C) 2009 Elsevier Inc. All rights reserved.