Dexamethasone lowers cytosolic pH in macrophages by altering alkalinizing pH‐regulatory mechanisms

The effect of dexamethasone on cytosolic pH (pH c ) in resident mouse peritoneal macrophages was investigated using the fluorescent probe 2′,7′‐ bis (carboxyethyl)‐5(6)‐carboxyfluorescein tetra‐acetoxymethyl ester (BCECF‐AM). Dexamethasone was found to significantly lower pH c and this reduction of pH c evolved gradually with time, was near maximal at 10 nM dexamethasone, and could be prevented by the glucocorticoid receptor antagonist RU‐38486. The lower pH c of dexamethasone‐treated cells was neither due to a reduction of cellular buffer capacity nor to an altered regulation of pH c by Na + /H + ‐exchange or by acidifying Na + ‐independent Cl − /HCO exchange, as assessed by studies of pH recovery after acute acid and alkali loads, respectively. Instead, an impaired pH c recovery by both the H + ‐ATPase and the alkalinizing Na + ‐dependent Cl − /HCO exchange was observed. This impairment was most likely not caused by an altered expression or localization of the 39‐κDa subunit of the proton pump. Dexamethasone treatment caused a reduction of pH c also in a HCO‐containing solution, suggesting that acid extrusion by both the H + ‐ATPase and Na + ‐dependent Cl − /HCO exchange is important for maintenance and regulation of macrophage resting pH c . The lowering of macrophage pH c might be one mechanism whereby glucocorticoids exert their anti‐inflammatory effects. J. Leukoc. Biol. 67: 876–884; 2000.