The Relationship between Phosphorylation Potential and Redox State in the Isolated Working Rabbit Heart

The effects of the cytosolic and mitochondrial redox state on the function and phosphorylation potential of working perfused rabbit hearts were studied. Hearts were perfused with glucose, while lactate, aminooxy-acetate (an inhibitor of the malate-aspartate shuttle). β-hydroxybutyrate, and pyruvate were sequentially added to the perfusate to manipulate the cytosolic and mitochondrial NAD+/NADH ratio. The phosphorylation potential and product of ADP and P1 were both found to be proportional to mitochondrial redox state. There was no overall relationship between cytosolic redox potential and the ratio, although at high mitochondrial NADH, there was a tendency for the states with more reduced cytoplasm to be associated with a lower phosphorylation potential. Cardiac output and dP/dt were decreased after 75 μM aminooxy-acetate was present for 15 min, and remained low when 0.5-1.0 mM β-hydroxybutyrate was added, even though the β-hydroxybutyrate period was characterized by both very low cytosolic NAD+/NADH and high mitochondrial NADH. Function returned to normal when the cytoplasm was oxidized by addition of 10 mM pyruvate, and although MVO2 rose from 4.0 ± 0.4 to 5.0 ± 0.5, this was not accompanied by statistical changes in either mitochondrial NADH or phosphorylation potential. Therefore, the cytosolic redox state may play a role in cardiac function, but has only a minor contribution to the regulation of the phosphorylation potential in the working perfused rabbit heart.