Cyclic adenosine monophosphate-mediated release of nitric oxide from canine cultured tracheal epithelium

Nitric oxide (NO) may play a part in pulmonary vascular regulation and bronchomotor control and has been detected in exhaled air. We report the release of NO from airway epithelial cells and its regulation by cyclic adenosine monophosphate (cAMP). To directly measure NO release, a highly specific amperometric sensor for NO made of Pt/Ir alloy coated with a three-layered membrane consisting of KCI, NO-selective resin, and normal silicon resin was developed. Immersion of this sensor in the medium containing canine cultured tracheal epithelium detected baseline levels of NO at 9.6 +/- 1.6 nM (mean +/- SE), which was reduced by NG-nitro-L-arginine methylester (L-NAME) but not by D-NAME. This inhibition was reversed by L-arginine. Addition of isoproterenol, 3-isobutyl-1-methylxanthine, and forskolin caused a rapid increase in NO, an effect that was not altered by Ca(2+)-free medium in the presence of the intracellular Ca2+ chelator BAPTA-AM and the calmodulin antagonist W-7. Bradykinin, ionomycin, and ATP were without effect on NO release. The forskolin-induced NO release was accompanied by intracellular accumulation of cAMP and Ca2+. In contrast, bradykinin increased intracellular Ca2+ but not cAMP levels. Cytochemistry of cultured tracheal epithelium showed a positive staining with NADPH diaphorase activity. These results suggest that airway epithelial cells spontaneously release NO and that the release may be stimulated specifically through cAMP-dependent mechanism.