Abstract 14853: Ischemic Preconditioning Protects Mitochondria Against Respiratory Failure Secondary To Ischemia-reperfusion Independently Of Cytosolic Signaling And Permeability Transition. Role Of Connexin43.
Ischemic preconditioning (IP) protects against reperfusion injury. Several membrane receptor-triggered cascades involving kinase pathways that ultimately prevent mitochondrial permeability transition (MPT) participate in protection.
Hypothesis: IP may attenuate the alterations caused by ischemia/reperfusion (IR) on mitochondrial respiration by mechanisms independent of cytosolic signaling and MPT.
Methods: Subsarcolemmal (SSM) and interfibrillar (IFM) mitochondria were isolated from rat hearts previously submitted to sublethal IR (20min), preceded or not by 2 brief episodes of IP. In paralel, isolated SSM and IFM obtained from normoxic hearts were resuspended in a substrate, ADP-containing buffer at pH6.4, and were allowed to exhaust O2 (Clark electrode). After 15min of simulated ischemia mitochondria were switched to an oxygenated, substrate-containing buffer at pH7.4 (IR group). This protocol was preceded or not by a brief episode of simulated IR (IP group). Respiration was monitored at different time points using substrates for each respiratory complex.
Results: Sublethal IR did not result in LDH release in rat myocardium. However, reperfusion resulted in depressed ADP-stimulated respiration and lower respiratory control rate, both in mitochondria isolated from previously IR rat hearts and in mitochondria submitted to in vitro IR, independently of the substrate used. Respiratory reduction was significantly attenuated by IP in SSM from both preparations, but this protection was less pronounced or absent in IFM. The alterations induced by IR and the protection afforded by IP could be reproduced in mitochondria from genetically modified mice lacking cyclophilinD (CyD KO) resistant to MPT. Because connexin 43 (Cx43) is present in SSM but not in IFM we analyzed its role in mitochondrial IP in mice in which Cx43 was replaced by Cx32 (Cx43KI32) and wild-types. IP significantly improved respiratory control rate after IR in wild-types but not in Cx43KI32.
Conclusions: These results suggest that part of the protective effect of IP against reperfusion injury is triggered and effected within mitochondria in the absence of cytosolic signaling by mechanisms independent of MPT, and that Cx43 participates in this “mitochondrial preconditioning”.
- © 2011 by American Heart Association, Inc.