Voltage-dependent Na+-HCO3? cotransporter and Na+/H+ exchanger are involved in intracellular pH regulation of cultured mature rat cerebellar oligodendrocytes

Abstract

Intracellular pH (pH_i) was measured at 37°C in mature rat cerebellar oligodendrocytes dissociated in culture by using the pH‐sensitive probe BCECF. Cells were identified by anti‐galactocerebroside antibody. The mean steady‐state pH_i was 7.02 in the absence of CO₂/bicarbonate (Hepes‐buffered solution) at an external pH of 7.40 and 7.04 in 5% CO₂/25 mM bicarbonate‐buffered solution at the same external pH; this value was modified neither by the removal of external chloride nor by the addition of the chloride‐coupled transport blocker DIDS. In both external solutions steady‐state pH_i values were strongly dependent on external pH. In Hepes‐buffered solution pH_i recovery following an acid load required external Na⁺ and was completely inhibited by amiloride, indicating the presence of a Na⁺/H⁺ exchanger. In CO₂/bicarbonate‐buffered solution amiloride partially reduced the pHi recovery rate, indicating the presence of a bicarbonate‐dependent pH_i regulating mechanism. Membrane depolarization induced by increasing external K⁺ concentration elicited an alkalinization only in the presence of external Na⁺ and bicarbonate. Analysis of the calculated HCO₃ fluxes with respect to membrane potential indicated that these fluxes were mediated by a Na⁺‐HCO₃ cotransport with a stoichiometry of 1:3. These results demonstrate that a Na⁺/H⁺ exchanger and a Na⁺ HCO₃ cotransporter are involved in pH_i regulation of mature oligodendrocytes. GLIA 19:74–84, 1997.