The effect of NO-donors on chloride efflux, intracellular Ca(2+) concentration and mRNA expression of CFTR and ENaC in cystic fibrosis airway epithelial cells.

Since previous studies showed that the endogenous bronchodilator, S-nitrosglutathione (GSNO), caused a marked increase in CFTR-mediated chloride (Cl−) efflux and improved the trafficking of CFTR to the plasma membrane, and that also the nitric oxide (NO)-donor GEA3162 had a similar, but smaller, effect on Cl− efflux, it was investigated whether the NO-donor properties of GSNO were relevant for its effect on Cl− efflux from airway epithelial cells. Hence, the effect of a number of other NO-donors, sodium nitroprusside (SNP), S-nitroso-N-acetyl-dl-penicillamine (SNAP), diethylenetriamine/nitric oxide adduct (DETA-NO), and diethylenetriamine/nitric oxide adduct (DEA-NONOate) on Cl− efflux from CFBE (∆F508/∆F508-CFTR) airway epithelial cells was tested. Cl− efflux was determined using the fluorescent N-(ethoxycarbonylmethyl)-6-methoxyquinoliniu bromide (MQAE)-technique. Possible changes in the intracellular Ca2+ concentration were tested by the fluorescent fluo-4 method in a confocal microscope system. Like previously with GSNO, after 4h incubation with the NO-donor, an increased Cl− efflux was found (in the order SNAP>DETA-NO>SNP). The effect of DEA-NONOate on Cl− efflux was not significant, and the compound may have (unspecific) deleterious effects on the cells. Again, as with GSNO, after a short (5min) incubation, SNP had no significant effect on Cl− efflux. None of the NO-donors that had a significant effect on Cl− efflux caused significant changes in the intracellular Ca2+ concentration. After 4h preincubation, SNP caused a significant increase in the mRNA expression of CFTR. SNAP and DEA-NONOate decreased the mRNA expression of all ENaC subunits significantly. DETA-NO caused a significant decrease only in α-ENaC expression. After a short preincubation, none of the NO-donors had a significant effect, neither on the expression of CFTR, nor on that of the ENaC subunits in the presence and absence of l-cysteine. It can be concluded that the effect of GSNO on Cl− efflux is, at least in part, due to its properties as an NO-donor, and the effect is likely to be mediated by CFTR, not by Ca2+-activated Cl− channels.