Determination of intracellular pH in the Langendorff-perfused guinea-pig heart by 31P nuclear magnetic resonance spectroscopy.

The 31P NMR spectrum of freshly prepared guinea-pig heart perfused in the Langendorff mode at 37 degrees C with medium containing either glucose or pyruvate as an energy source exhibited no inorganic phosphate peak making the determination of intracellular pH from the chemical shift of this peak impossible. By incorporating 2-deoxyglucose-6-phosphate into the heart to act as an alternative pH indicator, intracellular pH was determined to be 6.98 +/- 0.02 (mean +/- S.E.M. for eight animals). 2-Deoxyglucose was not taken up and phosphorylated by guinea-pig heart in the presence of glucose. Uptake and phosphorylation did proceed if glucose was omitted from the perfusion medium, but a large inorganic phosphate peak was present in the initial spectrum prior to 2-deoxyglucose addition. With pyruvate as sole energy source, an inorganic phosphate peak was absent initially and 2-deoxyglucose was taken up and phosphorylated. During a 12 min period of global ischaemia at 20 degrees C, when inorganic phosphate was visible together with 2-deoxyglucose-6-phosphate, a close correlation was found between the pH estimated from the chemical shift of inorganic phosphate and 2-deoxyglucose-6-phosphate over the pH range 6.3 to 6.9.