Effects of lactate on bovine heart mitochondria-mediated metmyoglobin reduction

Our objective was to determine the combined effects of lactate, LDH, and NAD on metmyoglobin reduction in mitochondria isolated from bovine cardiac muscle. Mitochondria were reacted with various combinations of lactate, LDH, NAD, and mitochondrial inhibitors, and oxygen consumption was measured using a Clark oxygen electrode. Mitochondria (3 mg/mL) and bovine metmyoglobin (0.15 mM) also were reacted with substrates/enzymes/inhibitors to determine mitochondria-mediated metmyoglobin reduction in vitro. Combining lactate-LDH-NAD with isolated mitochondria increased oxygen consumption as well as metmyoglobin reduction compared with those of either control mitochondria (without lactate) or mitochondria with added lactate, at pH 5.6 and 7.4 (p < 0.05). The addition of mitochondrial and LDH inhibitors to lactate-LDH-NAD decreased oxygen consumption and metmyoglobin reduction (p < 0.05). NADH formed from lactate-LDH-NAD can be used for nonenzymatic (via the electron transport chain) and enzymatic (NADH-dependent metmyoglobin reductase) metmyoglobin reduction.