Oxidative phosphorylation in isolated canine myocardial mitochondria. Effects of in vitro volume dilution, lactate, phosphate, and calcium addition, and lactic acidosis.

Oxidative phosphorylation of isolated canine myocardial mitochondria was evaluated after exposure to different concentrations of phosphate (5-50 mM), lactate ion in excess (5-40 mM, pH 7.4), and calcium (50-200 microM), to lactic acidosis (pH 6.3), and to mitochondrial protein dilution (in vitro volume expansion) for 10 min to 8 hr. The influence of phosphate and lactate ion addition, lactic acidosis, and in vitro volume expansion on mitochondrial function were studied in the isolation medium (0.18 M KCl, 0.5% bovine serum albumin (BSA) with or without Tris-EDTA, pH 7.4) prior to evaluation of mitochondrial function in the assay medium (0.25 M sucrose, 10 mM Tris-HCl, and 10 mM inorganic phosphate, pH 7.4). The effect of calcium addition was assessed in the assay medium. The results of these studies demonstrate that each of these interventions detrimentally alters mitochondrial oxidative phosphorylative ability. The most severe mitochondrial function impairment resulted from phosphate (5-50 mM) or calcium (50 or 200 microM) addition, each of which decreased the rate of oxygen consumption by 40% or greater. The mitochondrial functional alterations resulting from the interventions that were studied persisted after their removal, but the detrimental effect of phosphate addition and in vitro volume expansion was partially corrected by the addition of cytochrome c. The data are consistent with the possibility that each of these interventions is capaable of altering mitochondrial function but suggest that phosphate and calcium ion accumulation exert the most important detrimental effect on oxidative phosphsorylation in isolated canine cardiac mitochondria.