Comparison of intracellular pH measurements by 31P NMR and weak acid partitioning in Chinese hamster ovary fibroblasts.

Intracellular pH measurements obtained by 31P NMR and DMO partitioning are compared. A continuous-flow culture system was used to measure the intracellular pH of Chinese hamster ovary fibroblasts in response to changes in the extracellular pH. These measurements were repeated with the CHO cells in suspension and under similar experimental conditions using the weak acid partitioning technique employing 14C-DMO. It is shown that the pHi values are identical, within experimental error, for both techniques in the 6.80-7.70 pH range, with the DMO technique giving slightly more acidic intracellular pH in the 6.00-6.80 range. It is concluded that both techniques give similar values for intracellular pH in the physiological range, with the DMO partitioning giving more acidic values at pH's less than 6.80. The range of validity for pHi measurements using 31P NMR lies between 6.70 and 7.50.