STUDIES OF ACIDOSIS IN THE ISCHEMIC HEART BY PHOSPHORUS NUCLEAR MAGNETIC-RESONANCE

Phosphorus-nuclear-magnetic-resonance measurements were made on perfused rat hearts at 37°C. With the improved sensitivity obtained by using a wide-bore 4.3 T superconducting magnet, spectra could be recorded in 1 min. The concentrations of ATP, phosphocreatine and P(i) and, from the position of the P(i) resonance, the intracellular pH (pH(i)) were measured under a variety of conditions. In a normal perfused heart pH(i)=7.05±0.02 (mean ± S.E.M. for seven hearts). During global ischaemia pH(i) drops to 6.2±0.06 (mean ± S.E.M.) in 13 min in a pseudoexponential decay with a rate constant of 0.25 min-1. The relation between glycogen content and acidosis in ischaemia is studied in glycogen-depleted hearts. Perfusion of hearts with a buffer containing 100 mM-Hepes before ischaemia gives a significant protective effect on the ischaemic myocardium. Intracellular pH and ATP and phosphocreatine concentrations decline more slowly under these conditions and metabolic recovery is observed on reperfusion after 30 min of ischaemia at 37°C. The relation between acidosis and the export of protons is discussed and the significance of glycogenolysis in ischaemic acid production is evaluated.