Low Ambient [Cl−] Increases Ca2+ Mobilization and Stimulates Nitric Oxide and Prostaglandin E2 Production in Human Bronchial Epithelial Cells

Changes in ionic composition of airway surface fluid may modulate airway epithelial functions. We tested the hypothesis that fluctuations of ambient ionic composition could affect airway epithelial Ca2+ dynamics and Ca2+-dependent cellular functions, including NO release and PGE2 production in vitro. The responses of intracellular Ca2+ concentration ([Ca2+]i) to changes in extracellular Cl− and Na+ concentrations ([Cl−]e, [Na+]e) in the human bronchial epithelial cell line, 16HBE cells, were measured by the fura-2 method. The NO release to the medium after lowering [Cl−]e was measured by an amperometric NO sensor. PGE2 production was measured by radioimmunoassay. Changing to isotonic low [Cl−]e solution by substitution with gluconate caused a sustained increase in [Ca2+]i in a concentration-dependent manner, with the maximal [Ca2+]i increase from the baseline level being 243 ± 110 nM with Cl-free solution. The effect was not altered by thapsigargin but abolished by EGTA and by Cl channel blockers, including diphenylamine-2-carboxylate, disodium 4,4′-diisothiocyanatostilbene-2,2′-disulfonate, and disodium cromoglycate. In contrast, the effect of reduction of [Na+]e by substitution with N-methyl-D-glucamine+ on [Ca2+]i was less than that of reduction of [Cl−]e. The reduction of [Cl−]e caused a concentration-dependent rise in NO contents in the medium and PGE2 production. This release of NO was inhibited by EGTA but not by dexamethasone pretreatment. These results suggest that the decrease in ambient [Cl−] induces Ca2+ mobilization probably through Ca2+ influx, followed by the release of NO and PGE2, thereby modulating various cellular functions.