The regulation of intracellular pH in cultured astrocytes and neuroblastoma cells, and its dependence on extracellular pH in a HCO3-free solution.

Microspectrofluorometry was used to study the regulation of intracellular pH (pHi) in 2',7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein (BCECF)-loaded astrocytes and the neuroblastoma-glioma cells of the NG 108-15 line. The cells rapidly regulated pHi during an acid transient induced by an NH4+ prepulse. This regulation was blocked by removal of Na+, or by addition of 1 mM amiloride. The back regulation was also inhibited when extracellular pH (pHc) was lowered. Furthermore, when cells were exposed to buffer with reduced or increased pHc, pHi changed in parallel. Thus, although these cells possess at least one efficient H+ extrusion mechanism, which is likely to be the ubiquitous Na+/H+ antiporter, they fail to regulate pHi to a normal value unless pHc is held constant. The implications of these findings are discussed.