Regulation of intracellular pH in neuronal and glial tumour cells, studied by multinuclear NMR spectroscopy

The effect of extracellular pH (pH e ) on intracellular pH (pH i ) and cellular metabolism was examined by multinuclear NMR spectroscopy of cells in vivo and in vitro . A decrease in pH e from 7.4 to 6.4 led to a significant drop in pH i , in both neuronal and glial tumour cells, as detected by in vivo 31 P NMR of cells embedded in basement membrane gel threads. A more than 50% decrease in both the phosphocreatine (PCr) level and derivatives of glycolysis (i.e., glycerol 3‐phosphate) was observed, concomitantly to the fall in pH i . A 50% decrease in intracellular lactate levels was seen in in vivo 1 H NMR spectra under these conditions. Reperfusion with fresh medium (pH e 7.4) resulted in the full recovery of pH i , simultaneously with an increase in both PCr and intracellular lactate back to their control levels. Perchloric acid and lipid extract measurements confirmed the observations made by in vivo 31 P and 1 H NMR spectroscopy and further showed a decrease both in tricarboxylic acid cycle activity and phospholipid synthesis. The data revealed no significant differences between the neuronal and glial tumour cells investigated. pH i measurements in the presence of inhibitors of the various pH regulatory mechanisms showed that the Na + /H + exchanger, the carbonic anhydrase and at least one of the bicarbonate‐transport systems are involved in pH regulation of both cell types. The results suggest that Na + /H + exchange is the preferred mechanism by which both neuronal and glial cells regulate their pH i after extracellular acidification.