Intracellular pH determination by ¹³C-NMR spectroscopy

A noninvasive method for the determination of pH by the ¹³C-nuclear magnetic resonance (NMR) chemical shift of the C-3 carbon of sn-glycerol 3- phosphate is described. Nonlinear least-squares analysis of the chemical shift variation of the C-3 resonance of sn-glycerol 3-phosphate with pH at 37°C in solutions and in perchloric acid extracts of tissue yielded a pK(a) of 6.2, making it a very sensitive indicator of pH in the approximate range of 5-7. Intracellular pH determined by the present ¹³C-NMR method correlated well with simultaneous measurements of pH by ³¹P-NMR spectroscopy over a wide range during normal perfusion and ischemic conditions in intact rat hearts. These findings indicate that this approach is particularly suited for quantification of intracellular pH over the physiological range in intact tissues and that observed in ischemic myocardium.