029 Rapid effects of dexamethasone on intracellular pH and K+ transport in human airway epithelium☆

Introduction Glucocorticoids (GC) are the main treatment of asthma. GC are anti-inflammatory molecules classically described to act via a genomic pathway. Similarly to many steroid hormones, GC also induced non-genomic responses which might explain some of their rapid clinical effect. In airway epithelium, K + transport maintains the electrochemical gradient for transepithelial ion transport which controls the airway luminal water content. Several types of K + channels are involved and their differential regulation might play the role of “switch” between epithelial absorption and secretion. Here, we investigated the non-genomic effect of the synthetic glucocorticoid dexamethasone, on intracellular pH (pH i ) regulation and on potassium (K + ) transports in human bronchial epithelial cells. Methods We investigated the dexamethasone effect on pH i recovery after an acid load by fluorescence microscopy technique on human bronchial epithelial 16HBEl4o- cells loaded with BCECF-AM. The dexamethasone effect on K + conductance was investigated using whole-cell patch-clamp recording. Results After an acid load, a spontaneous pH i ; regulation occurred (basal recovery rate: 0.05 ± 0.02 pH units/min, n = 8). Dexamethasone (1 nM) stimulated the pH i ; recovery to a rate of 0.11 ± 0.03 pH units/min, n = 8. Both external Na+ removal and the Na+/H+ exchanger inhibitor, 5-(n-ethyl-N-isopropyl) amiloride inhibited the basal pH i ; recovery and the dexamethasone stimulation of pH i recovery. The rapid effect of dexamethasone on pH i ; was not affected by inhibitor of transcription, cycloheximide or by the classical GC and mineralocorticoid receptors antagonists, RU486 and spironolactone respectively. The response to dexamethasone was reduced by the inhibitors of adenylated cyclase, cAMP dependant protein kinase (PKA) and Mitogen-Activated Protein kinase (ERK1/2) activities. In addition, within 5 minutes, dexamethasone at 1 pM, 1 nM, and 1μM stimulated outwardly rectified currents by 61.2% (n = 15), 137.7% (n = 13), and 137.8% (n = 13) respectively. The dexamethasone effect on the whole current was inhibited by the 2 potassium channels blockers, baryum and tetra-ethyl-ammonium. Conclusions Our results demonstrated, that dexamethasone at physiological concentration, rapidly regulated pH i and K + transport in human bronchial epithelial cells via a non-genomic mechanism which does not involved the classical glucocorticoid nor mineralocorticoid receptor.