Rapid effects of dexamethasone on intracellular pH and Na ⁺/H⁺ exchanger activity in human bronchial epithelial cells

Glucocorticoids have been shown to produce rapid nongenomic responses in airway epithelia. By using an intracellular pH (pH_i) spectrofluorescence imaging system and the NH₄Cl acid-loading technique, we have shown that the synthetic glucocorticoid, dexamethasone, accelerated intracellular pH recovery after an acid load in a human bronchial epithelial cell line (16HBE14o^- cells). Exposure to NH₄Cl (20 mM) elicited an intracellular acidification, followed by a pH_i recovery. Inhibition of the Na⁺/H⁺ exchanger decreased the steady-state pH_i and antagonized the dexamethasone stimulation of pH_i regulation. The rapid effect of dexamethasone on pH_i was neither affected by the inhibitor of transcription, cycloheximide, nor by the classical glucocorticoid and mineralocorticoid receptors antagonists, RU486 and spironolactone, respectively. The dexamethasone effect on pH_i regulation was reduced by inhibitors of adenylate cyclase, cAMP-dependent protein kinase and mitogen-activated protein kinase (ERK1/2). By using a PepTag assay system and Western blotting, we have shown that dexamethasone stimulated cAMP-dependent protein kinase and mitogen-activated protein kinase activities. Taken together our results provide evidence for the rapid stimulation of Na ⁺/H⁺ exchange activity by glucocorticoids in bronchial epithelial cells via a nongenomic mechanism involving cAMP-dependent protein kinase and mitogen-activated protein kinase ERK1/2 pathways.