REGULATION OF INTRACELLULAR PH IN NEURONAL AND GLIAL TUMOR-CELLS, STUDIED BY MULTINUCLEAR NMR-SPECTROSCOPY

The effect of extracellular pH (pH(e)) on intracetlular pH (pH(i)) and cellular metabolism was examined by multinuclear NMR spectroscopy of cells in vivo and in vitro. A decrease in pH, 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 vive P-31 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 H-1 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 P-31 and 1H 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, 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.