We have studied the characteristics of pH(i) regulation at different stages of rat oligodendrocyte differentiation in primary culture. pH(i) was measured at 37 degrees C using the pH-sensitive fluorescent probe BCECF. In immature oligodendrocyte progenitor (OLP), three distinct ionic mechanisms were involved in pH(i) regulation: (i) a sodium-independent Cl(-)/HCO(-)(3) exchanger, (ii) a Na(+)/H(+) exchanger and (iii) a voltage-dependent Na(+)-HCO(-)(3) cotransporter. The two latter mechanisms were also detected in more differentiated pro-oligodendrocytes and in mature oligodendrocytes whereas the Cl(-)/HCO(-)(3) exchanger was not active in these two later stages of differentiation. The presence of this Cl(-)/HCO(-)(3) exchanger (that acts as a chronic acidifying mechanism) only in immature OLP maintains in these cells a steady-state pH(i) value significantly lower than values measured in more differentiated cells. The possible involvement of this pH(i) change in triggering cell differentiation is discussed.
Intracellular pH (pHi) 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 pHi 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 pHi values were strongly dependent on external pH. In Hepes‐buffered solution pHi 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 pHi 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 pHi regulation of mature oligodendrocytes. GLIA 19:74–84, 1997. © 1997 Wiley‐Liss, Inc.
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