Postconditioning modulates ischemia-damaged mitochondria during reperfusion.

Cardiac ischemia damages the mitochondrial electron transport chain and the damage persists during reperfusion. Ischemic postconditioning (PC), applied during early reperfusion, decreases cardiac injury. This finding suggests that the ischemia-damaged mitochondria can be regulated to decrease cardiac injury. The reversible blockade of electron transport during ischemia prevents damage to mitochondria. We propose that the targets of PC cytoprotective signaling are mitochondria damaged by ischemia. Thus, if ischemia-mediated mitochondrial damage is prevented, PC at the onset of reperfusion will not result in additional protection. Isolated, Langendorff-perfused adult rat hearts underwent 25-minute global ischemia and 30-minute reperfusion. Amobarbital (2.5 mM) was used to reversibly inhibit electron transport during ischemia. PC (6 cycles of 10-second ischemia-reperfusion) was applied at the onset of reperfusion. Subsarcolemmal and interfibrillar mitochondria were isolated after reperfusion. Blockade of electron transport with amobarbital only during ischemia preserved oxidative phosphorylation and decreased myocardial injury. PC, after untreated ischemia, decreased cardiac injury without improvement of oxidative phosphorylation. Blockade of electron transport during ischemia or PC improved calcium tolerance and inner membrane potential in subsarcolemmal mitochondria after reperfusion. In hearts treated with amobarbital before ischemia, PC did not provide further protection. Thus, PC protects myocardium via the regulation of ischemia-damaged mitochondria during early reperfusion.