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Background and purpose: The mitochondrial permeability transition pore (mPTP), an energy-dissipating channel activated by calcium, contributes to reperfusion damage by depolarizing the mitochondrial inner membrane potential. As mitochondrial Ca 2 þ overload is a main inductor of mPTP opening, we examined the effect of Ru 360 , a selective inhibitor of the mitochondrial calcium uptake system against myocardial damage induced by reperfusion in a rat model. Experimental approach: Myocardial reperfusion injury was induced by a 5-min occlusion of the left anterior descending coronary artery, followed by a 5-min reperfusion in anaesthetized open-chest rats. We measured reperfusion-induced arrhythmias and functions indicative of unimpaired mitochondrial integrity to evaluate the effect of Ru 360 treatment. Key results: Reperfusion elicited a high incidence of arrhythmias, haemodynamic dysfunction and loss of mitochondrial integrity. A bolus intravenous injection of Ru 360 (15-50 nmol kg À1 ), given 30-min before ischaemia, significantly improved the above mentioned variables in the ischaemic/reperfused myocardium. Calcium uptake in isolated mitochondria from Ru 360 -treated ventricles was partially diminished, suggesting an interaction of this compound with the calcium uniporter. Conclusions and implications:We showed that Ru 360 treatment abolishes the incidence of arrhythmias and haemodynamic dysfunction elicited by reperfusion in a whole rat model. Ru 360 administration partially inhibits calcium uptake, preventing mitochondria from depolarization by the opening of the mPTP. We conclude that myocardial damage could be a consequence of failure of the mitochondrial network to maintain the membrane potential at reperfusion. Hence, it is plausible that Ru 360 could be used in reperfusion therapy to prevent the occurrence of arrhythmia.

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