SIMULTANEOUS INTRACELLULAR AND EXTRACELLULAR PH MEASUREMENT IN THE HEART BY F-19 NMR OF 6-FLUOROPYRIDOXOL

6-Fluoropyridoxol (6-FPOL) was evaluated as a simultaneous indicator o f intracellular and extracellular pH and, hence, pH gradient in perfus ed rat hearts. After infusion, F-19 NMR spectra rapidly showed two wel l-resolved peaks assigned to the intracellular and extracellular compa rtments, and pH was calculated on the basis of chemical shift with res pect to a sodium trifluoroacetate standard. To demonstrate use of this molecule, dynamic changes in myocardial pH were assessed with a time resolution of 2 min during respiratory and metabolic alkalosis or acid osis and ischemia. For a typical heart, intracellular pH (pHi) = 7.14 +/- 0.01 and extracellular pH (pHe) = 7.52 +/- 0.02. In response to me tabolic alkalosis, pHi remained relatively constant and the pH gradien t increased. In contrast, respiratory challenge caused a significant i ncrease in pHi. Independent measurements using pH electrodes and P-31 NMR confirmed validity of the F-19 NMR results.