P-31 NUCLEAR MAGNETIC-RESONANCE MEASUREMENT OF CARDIAC PH IN PERFUSED GUINEA-PIG HEARTS

Cardiac pH was measured by 31P nuclear magnetic resonance spectroscopy. Measurements were made on 23 control hearts perfused with Krebs-Henseleit bicarbonate buffer containing potassium phosphate (1.2 mm) at pH 7.4, but with no external bathing medium. Only one very weak peak could be observed in the orthophosphate region at pH 7.0±0.1. Previous reports have shown a relatively strong line in this region at pH 7.4. The pH 7.0 value was confirmed by perfusion with Krebs-Henseleit bicarbonate-phosphate at pH 7.5, but this time in the presence of an external bathing medium composed of the same buffer. Two peaks were observed in the orthophosphate region. One was at pH 7.0 while the other was at pH 7.5. Replacement of the external bathing medium and perfusate by one free of phosphate (Krebs-Henseleit bicarbonate-Tris-HCl, 1.2 mm Tris plus 1.2 mm KCl, pH 7.4) caused the pH 7.5 peak to disappear but did not affect the pH 7.0 line. Thus, cardiac pH in well-oxygenated, Krebs-Henseleit bicarbonate-phosphate perfused hearts is 7.0, not 7.4. In addition, the magnitude of the observed acidosis associated with coronary artery ligation was about two times smaller (∼0.4 pH units) than that seen in the other studies owing to this difference in control pH. The current value of cardiac pH determined by nuclear magnetic resonance is now in excellent agreement with the values determined by more conventional methods. © 1979.