Sodium- and bicarbonate-independent regulation of intracellular pH in culture mouse astrocytes.

The intracellular pH (pHi) of cultured mouse astrocytes was measured with double-barrelled pH-sensitive microelectrodes. In bicarbonate-buffered saline pHi was 7.05 and in HEPES-buffered saline 6.68. In both solutions H+ was not in electrochemical equilibrium; pHi was 0.7-1 pH unit more alkaline than expected from passive H+ distribution. Cells were acidified by applying NH4+ and the subsequent regulation of pHi was studied in bicarbonate-free saline. The mean rate of pHi recovery was 0.2 pH units min-1 which was not changed by amiloride or by removal of external Na+. Thus, the cells recovered from an acid load independently of Na(+)-H+ exchange, Na(+)-HCO3- cotransport or any other bicarbonate- or Na(+)-dependent mechanism.