Rapid non‐genomic inhibition of ATP‐induced Cl − secretion by dexamethasone in human bronchial epithelium

A non‐genomic antisecretory role for dexamethasone at low concentrations (0.1 n m to1 μ m ) is described in monolayers of human bronchial epithelial cells in primary culture and in a continuous cell line (16HBE14o‐ cells). Dexamethasone produced a rapid decrease of [Ca 2+ ] i (measured with fura‐2 spectrofluorescence) to a new steady‐state concentration. After 15 min exposure to dexamethasone (1 n m ), [Ca 2+ ] i was reduced by 32 ± 11 n m ( n = 7 , P < 0.0001 ) from a basal value of 213 ± 36 n m ( n = 7 ). We have shown previously that aldosterone (1 n m ) also produces a rapid fall in [Ca 2+ ] i ; however, after the decrease in [Ca 2+ ] i induced by dexamethasone, subsequent addition of aldosterone did not produced any further lowering of [Ca 2+ ] i . The rapid response to dexamethasone was insensitive to pretreatment with cycloheximide and unaffected by the glucocorticoid type II and mineralocorticoid receptor antagonists RU486 and spironolactone, respectively. The rapid [Ca 2+ ] i decrease induced by dexamethasone was inhibited by the Ca 2+ ‐ATPase pump inhibitor thapsigargin (1 μ m ), the adenylate cyclase inhibitor MDL hydrochloride (500 μ m ) and the protein kinase A inhibitor Rp‐adenosine 3′,5′‐cyclic monophosphorothioate (200 μ m ), but was not affected by the protein kinase C inhibitor, chelerythrine chloride (0.1 μ m ). Treatment of 16HBE14o‐ cell monolayers with dexamethasone (1 n m ) inhibited the large and transient [Ca 2+ ] i increase induced by apical exposure to ATP (10 −4 m ). Dexamethasone (1 n m ) also reduced by 30 % the Ca 2+ ‐dependant Cl − secretion induced by apical exposure to ATP (measured as the Cl − ‐sensitive short‐circuit current across monolayers mounted in Ussing chambers). Our results demonstrate, for the first time, that dexamethasone at low concentrations inhibits Cl − secretion in human bronchial epithelial cells. The rapid inhibition of Cl − secretion induced by the synthetic glucocorticoid is associated with a rapid decrease in [Ca 2+ ] i via a non‐genomic mechanism that does not involve the classical glucocorticoid or mineralocorticoid receptor. Rather, it is a result of rapid non‐genomic stimulation of thapsigargin‐sensitive Ca 2+ ‐ATPase, via adenylate cyclase and protein kinase A signalling.