A NUCLEAR MAGNETIC-RESONANCE STUDY OF METABOLISM IN THE FERRET HEART DURING HYPOXIA AND INHIBITION OF GLYCOLYSIS

31P NMR was used to measure the relative concentrations of phosphorus-containing metabolites in Langendorff-perfused ferret hearts. Intracellular concentrations of inorganic phosphate ([Pi]i), phosphocreatine ([PCr]i), ATP ([ATP]i) and H+ (pHi) were monitored under control conditions and while oxidative phosphorylation and/or glycolysis were prevented. Mechanical performance was assessed by recording the pressure developed in a balloon placed in the left ventricle. When oxidative phosphorylation alone is prevented, the changes in pHi can account for a substantial part of the changes in developed pressure. The increase in [Pi]i probably also contributes to the decline of developed pressure. When oxidative phosphorylation was prevented under conditions in which the rate of glycolysis was also reduced, the more pronounced decline in developed pressure which occurs within 5 min cannot be accounted for by pHi changes and is probably not explained by the rise in [Pi]i or by the moderate fall of [ATP]i. The possibility that a fall in free energy change of hydrolysis of ATP may account for the decline of developed pressure under these conditions is considered but the evidence is equivocal. The hypoxic contracture which is subsequently observed under these conditions is probably adequately accounted for by the fall in [ATP]i, which reaches low levels at about the same time.