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

Abstract

A non‐genomic antisecretory role for dexamethasone at low concentrations (0.1 nm to1 μm) 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 [Ca2+]i (measured with fura‐2 spectrofluorescence) to a new steady‐state concentration. After 15 min exposure to dexamethasone (1 nm), [Ca2+]i was reduced by 32 ± 11 nm (n= 7, P < 0.0001) from a basal value of 213 ± 36 nm (n= 7). We have shown previously that aldosterone (1 nm) also produces a rapid fall in [Ca2+]i; however, after the decrease in [Ca2+]i induced by dexamethasone, subsequent addition of aldosterone did not produced any further lowering of [Ca2+]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 [Ca2+]i decrease induced by dexamethasone was inhibited by the Ca2+‐ATPase pump inhibitor thapsigargin (1 μm), the adenylate cyclase inhibitor MDL hydrochloride (500 μm) and the protein kinase A inhibitor Rp‐adenosine 3′,5′‐cyclic monophosphorothioate (200 μm), but was not affected by the protein kinase C inhibitor, chelerythrine chloride (0.1 μm). Treatment of 16HBE14o‐ cell monolayers with dexamethasone (1 nm) inhibited the large and transient [Ca2+]i increase induced by apical exposure to ATP (10−4m). Dexamethasone (1 nm) also reduced by 30 % the Ca2+‐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 [Ca2+]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 Ca2+‐ATPase, via adenylate cyclase and protein kinase A signalling.

Lipoxin A4 Stimulates a Cytosolic Ca2+Increase in Human Bronchial Epithelium

“…Monolayers of 1.2 cm 2 exposed surface area were mounted in a horizontal Ussing chamber between 0 and 3 days after the electrical resistance reached a maximum value (800 -1200 ohms) as previously described (27). To create a favorable electrochemical gradient for Cl Ϫ secretion, the basolateral side of the monolayer was bathed in HEPES-buffered KrebsHensleit solution, and the apical was bathed in a low Cl Ϫ solution (125 mM sodium gluconate, 15 mM NaCl, 5 mM KCl, 2 mM CaCl 2 , 1 mM MgCl 2 , 10 mM HEPES, pH 7.4, 280 -290 mOsmol).…”

Role of nitric oxide on purinergic signalling in the cochlea

“…It has been reported that in some acute clinical situations, the additional benefit of the use of high doses of glucocorticoids is due to their non-genomic effects [113]. The non-genomic effects of dexamethasone on the ATP-induced Ca 2+ signalling and the Cl − secretion in cultured human bronchial epithelial cell monolayers have been also reported [114]. The rapid non-genomic effects of glucocorticoids on human bronchial epithelia may have important clinical implications in the treatment of airway infections such as rhinitis, asthma, and cystic fibrosis [114].…”

“…The non-genomic effects of dexamethasone on the ATP-induced Ca 2+ signalling and the Cl − secretion in cultured human bronchial epithelial cell monolayers have been also reported [114]. The rapid non-genomic effects of glucocorticoids on human bronchial epithelia may have important clinical implications in the treatment of airway infections such as rhinitis, asthma, and cystic fibrosis [114]. A recent study showed the novel non-genomic role of glucocorticoids on NO production in acute myocardial ischemic injury [115].…”

Treating gliomas with glucocorticoids: from bedside to bench

“…These rapid effects are mediated by non-genomic pathways and are insensitive to inhibitors of transcription and of protein synthesis (reviewed in Falkenstein [22] and Stellato [86]). Some of these effects do not require GR transduction and are based on alterations of the physicochemical properties of the cell membrane that modify levels of intracellular calcium [94]. Other rapid effects of glucocorticoids involve activation of the GR.…”