THE REGULATION OF INTRACELLULAR PH IS STRONGLY DEPENDENT ON EXTRACELLULAR PH IN CULTURED RAT ASTROCYTES AND NEURONS

We studied the mechanisms regulating intracellular pH (pH(i)) in cultu red rat astrocytes and neurons, with particular reference to the influ ence of extracellular pH (pH(e)) on these mechanisms, using microspect rofluorometric monitoring from single cells, loaded with the pH-sensit ive fluorophore BCECF. The pH regulatory mechanisms differ between neu rons and astrocytes. The experimental data suggest the presence of a N a+/H+ and a Na+-independent HCO3-/Cl- exchanger in both types of cells , while astrocytes, in addition, utilise a Na+-dependent HCO3-/Cl- exc hanger for regulating acid transients. In both cell types the pH regul atory mechanisms are strongly dependent on pH(e). Thus, at pH, 6.85 or below, there was no recovery of pH(i). Steady state pH(i) was also st rongly dependent on pH(e), in both astrocytes and neurons. The pH(i) r ecovery following normalisation of pH(e) was very rapid, (indicating t hat a prolonged exposure to a low pH stimulates pH regulating mechanis ms), and was inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulphon ic acid (DIDS) and amiloride, or in the absence of Na+. The results ch allenge the concept of a H+-regulatory site solely at the internal sid e of the exchanger regulating pH(i) to a constant value.