Role of pH in protection by low sodium against hypoxic injury in isolated perfused rat livers

Background/Aims: The purpose of the present study was to characterize the role of Na⁺, pH and cellular swelling in the pathogenesis of hypoxic injury to rat livers. Methods and Results: When livers were perfused with hypoxic Krebs-Henseleit bicarbonate buffer (KHB) containing 143 mM Na⁺, release of LDH began after 30 min and was maximal after 60 min. In livers perfused with choline-substituted low-Na⁺ KHB (25 mM Na⁺), LDH release began after 60 min and peaked after 120 min or longer. Supplementation of KHB with mannitol, a permeant sugar with antioxidant properties, suppressed LDH release, whereas sucrose, an impermeant disaccharide, did not afford protection. At the end of hypoxic perfusions with KHB and low-Na⁺ KHB, liver weight was not different, whereas mannitol but not sucrose increased liver weight after hypoxia. At pH 7.4, monensin, a Na⁺-H⁺ ionophore, reversed protection against hypoxia by low-Na⁺ KHB (10 mM Na⁺) but had no effect at pH 6.8. As measured directly by confocal microscopy of biscarboxyethylcarboxyfluorescein fluorescence, pH was lower during perfusion with low-Na⁺ KHB than KHB. Conclusions: Cytoprotection by low Na⁺ was not mediated by prevention of Na⁺-dependent tissue swelling. Rather, promotion of intracellular acidification likely mediates cytoprotection in low-Na⁺ buffer.