MiP2005: Session 8

Mitochondrial Physiology Network 10.9: 96-97 (2005) - download pdf

 

Role of matrix calcium accumulation in mitochondrial permeability transition in postconditioned versus preconditioned myocardium.

Odile Gateau-Roesch, L Argaud, J Loufouat, E Couture-Lepetit, J Adobati, M Ovize

INSERM E0226 "Cardioprotection" - Laboratoire de Physiologie Lyon-Nord / Université Claude Bernard Lyon1 – Hospices Civils de Lyon, France. – roesch@rockefeller.univ-lyon1.fr

    Calcium is a major trigger of mitochondrial permeability transition. Inhibition of the mitochondrial permeability transition pore (mPTP) opening plays a key role in cardioprotection afforded by both postconditioning (PostC) and preconditioning (PreC). We investigated whether inhibition of mPTP in PostC and PreC might be related to a change in mitochondrial calcium after ischemia-reperfusion.

    Anesthetized NZW rabbits (n=9/group) underwent either no intervention (sham) or 30 min of ischemia (I) followed by 1 h of reperfusion R. Animals underwent either no intervention (control, C), PreC by 5 min ischemia / 5 min reperfusion, or PostC with 4 episodes of 1 min ischemia / 1 min reperfusion performed after 1 min of reperfusion after the 30 min ischemia. At the end of the protocol, area at risk mitochondria were isolated by differential centrifugations. Total mitochondrial calcium content was assessed after mineralisation by HNO3 and measured by Induced Coupled Plasma Atomic Emission Spectrometry (ICP AES). Using freezed/thawed detergent-treated mitochondria, ionized (free) mitochondrial calcium content was measured using a calibrated Ca2+‑selective microelectrode. We also assessed the Ca2+ resistance capacity CRC of mPTP defined as the calcium overload required to induce mPTP opening. Moreover we checked mitochondrial integrity by electron microscopy.

    In controls, CRC was significantly reduced with Ca2+ overload required for mPTP opening averaging 0.73 ± 0.16 µg calcium/mg of mitochondrial proteins versus 4.23 ± 0.17 in sham hearts (P<0.0001). PostC, as PreC attenuated CRC reduction with Ca2+ overload averaging 1.58 ± 0.14 and 1.91 ± 0.26 µg calcium/mg prot. respectively (P<0.005 versus C). When compared to shams (1.42 ± 0.09), total mitochondrial Ca2+ content was significantly increased in both controls (2.39 ± 0.43 µg calcium/mg prot.) and PostC (2.34 ± 0.37), but not in PreC group (1.29 ± 0.17). Similar patterns were obtained for ionized mitochondrial Ca2+ content with a significant difference (P<0.001) versus sham (0.16 ± 0.01 µg calcium/mg Prot.) in controls (0.61 ± 0.10) and PostC group (0.77 ± 0.15), but not in PreC (0.26 ± 0.05). Electron photomicrograph clearly showed a lot of swollen mitochondria with damaged cristae in control group myocardium, while many mitochondria in PreC and particularly in PostC group displayed  intact membranes and dense matrix.

    These data suggest that restoration of mitochondria integrity play a major role in cardioprotection by PreC and PostC treatment. Mitochondrial permeability transition may be regulated in different ways in postconditioning versus preconditioning since reduced susceptibility to calcium overload observed in PreC and PostC were not correlated with the same repartition of mitochondrial calcium in these 2 groups.


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