31P nuclear magnetic resonance evidence for the regulation of intracellular pH by Ehrlich ascites tumor cells

The phenomenon of intracellular pH (pHin) regulation in cultured Ehrlich ascites cells was investigated using 31P nuclear magnetic resonance (NMR) spectroscopy. Measurements were made with a Bruker WH 360 wide bore NMR spectrometer at a 31P frequency of 145.78 MHz. Samples at a density of 10(8) cells ml-1 were suspended in a final volume of 2 ml of growth medium in 10 mm diameter NMR tubes. Intracellular pH was calculated from the chemical shifts of either intracellular inorganic phosphate (Piin) or intracellular 2-deoxyglucose-6-phosphate (2dG6Pin). The sugar phosphate was used as a pH probe to supplement the Piin measurements, which could not always be observed. When available, the pHin calculated from the Piin peak was identical within experimental error to the pHin calculated from the 2dG6Pin peak. Intracellular pH was measured to be more alkaline than the medium at an external pH (pHex) below 7.1. Typical values were pHin = 7.00 for pHex = 6.50. These measurements were constant for times up to 165 min using well-energized, respiring cells. This pH gradient was seen to collapse immediately upon onset of anaerobic shock. Above a pHex of 7.2 there was no significant difference between pHin and pHex. These results unequivocally demonstrate the steady state nature of the pH regulation and its dependence upon energization.