Mitochondrial permeability transition in pH-dependent reperfusion injury to rat hepatocytes

To simulate ischemia and reperfusion, cultured rat hepatocytes were incubated in anoxic buffer at pH 6.2 for 4 h and reoxygenated at pH 7.4. During anoxia, intracellular pH (pH(i)) decreased to 6.3, mitochondria depolarized, and ATP decreased to <1% of basal values, but the mitochondrial permeability transition (MPT) did not occur as assessed by confocal microscopy from the redistribution of cytosolic calcein into mitochondria. Moreover, cell viability remained >90%. After reperfusion at pH 7.4, pH(i) returned to pH 7.2, the MPT occurred, and most hepatocytes lost viability. In contrast, after reperfusion at pH 6.2 or with Na⁺-free buffer at pH 7.4, pH(i) did not rise and cell viability remained >80%. After acidotic reperfusion, the MPT did not occur. When hepatocytes were reperfused with cyclosporin A (0.5-1 μM) at pH 7.4, the MPT was prevented and cell viability remained >80%, although phi increased to 7.2. Reperfusion with glycine (5 mM) also prevented cell killing but did not block recovery of pH(i) or the MPT. Retention of cell viability was associated with recovery of 30-40% of ATP. In conclusion, preventing the rise of pH(i) after reperfusion blocked the MPT, improved ATP recovery, and prevented cell death. Cyclosporin A also prevented cell killing by blocking the MPT without blocking recovery of pH(i). Glycine prevented cell killing but did not inhibit recovery of pH(i) or the MPT.