Intracellular pH regulation in rat Schwann cells

We examined H+ and HCO3- transport mechanisms that are involved in the regulation of intracellular pH of Schwann cells. Primary cultures of Schwann cells were prepared from the sciatic nerves of 1-3-day-old rats. pHi of single cells attached to cover slips was continuously monitored by measuring the absorbance spectra of the pH-sensitive dye dimethylcarboxyfluorescein incorporated intracellularly. The average pHi of neonatal Schwann cells bathed in HEPES mammalian solution was 7.17 +/- 0.02 (n = 32). In the nominal absence of HCO3-, pHi spontaneously recovered from an acute acid load induced by exposing the Schwann cells to 20 mM NH4+ (NH4+ prepulse). This pHi recovery from the acute acid load was totally inhibited in the absence of external Na+ or in the presence of 1 mM amiloride. In both cases, the pHi recovery was readily restored upon readdition of external Na+ or removal of amiloride. In the steady-state, addition of amiloride caused a small and slow decrease in pHi which was readily reversed upon removal of amiloride. In the presence of HCO3-, removal of external Cl- caused pHi to rapidly and reversibly increase by 0.23 +/- 0.03 (n = 15) and the initial rate of alkalinization was 20.6 +/- 2.7 x 10(-4) pH/sec. In the absence of external Na+, removal of bath Cl- still caused pHi to increase by 0.15 +/- 0.02 and the initial rate of pHi increase was not significantly altered. In the nominal absence of HCO3-, removal of bath Cl- caused pHi to increase very slightly (0.05 +/- 0.01) with an initial dpHi/dt of only 4.4 +/- 0.2 x 10(-4) pH/sec (n = 4). Addition of 100 microM DIDS did not inhibit the pHi increase caused by removal of bath Cl-. These data indicate that 1) Rat Schwann cells regulate their pHi via an Na-H exchange mechanism which is moderately active at steady-state pHi. 2) In the presence of HCO3-, there is a Na-independent Cl-HCO3 (base) exchanger which also contributes to regulation of intracellular pH in Schwann cells.