Influence of volume dilution, lactate, phosphate, and calcium on mitochondrial functions

Oxidative phosphorylation of isolated canine myocardial mitochondria has been evaluated after exposure to different concentrations of phosphate (5--50 mM), lactate ion in excess (5--40 mM, pH 7.4), calcium (50--270 nmol/mg protein), to lactic acidosis (pH 6.3), and to mitochondrial protein dilution (in vitro volume expansion) for 10 min to 8 h. 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% BSA (bovine serum albumin), 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 functional impairment resulted from phosphate or calcium addition. The detrimental effect of phosphate and in vitro volume expansion was partially corrected by the addition of cytochrome c.