The regulation of intracellular pH is strongly dependent on extracellular pH in cultured rat astrocytes and neurons.

Abstract

We studied the mechanisms regulating intracellular pH (pHi) in cultured rat astrocytes and neurons, with particular reference to the influence of extracellular pH (pHe) on these mechanisms, using microspectrofluorometric monitoring from single cells, loaded with the pH-sensitive fluorophore BCECF. The pH regulatory mechanisms differ between neurons and astrocytes. The experimental data suggest the presence of a Na+/H+ and a Na(+)-independent HCO3-/Cl- exchanger in both types of cells, while astrocytes, in addition, utilise a Na(+)-dependent HCO3-/Cl- exchanger for regulating acid transients. In both cell types the pH regulatory mechanisms are strongly dependent on pHe. Thus, at pHe 6.85 or below, there was no recovery of pHi. Steady state pHi was also strongly dependent on pHe, in both astrocytes and neurons. The pHi recovery following normalisation of pHe was very rapid, (indicating that a prolonged exposure to a low pH stimulates pH regulating mechanisms), and was inhibited by 4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid (DIDS) and amiloride, or in the absence of Na+. The results challenge the concept of a H(+)-regulatory site solely at the internal side of the exchanger regulating pHi to a constant value.