Hydrogen sulfide decreases beta-adrenergic agonist-stimulated lung liquid clearance by inhibiting ENaC-mediated transepithelial sodium absorption

摘要

In pulmonary epithelia, 3-adrenergic agonists regulate the membrane abundance of the epithelial sodium channel (ENaC) and, thereby, control the rate of transepithelial electrolyte absorption. This is a crucial regulatory mechanism for lung liquid clearance at birth and thereafter. This study investigated the influence of the gaseous signaling molecule hydrogen sulfide (H_2S) on beta-adrenergic agonist-regulated pulmonary sodium and liquid absorption. Application of the H_2S-liberating molecule Na_2S (50 muM) to the alveolar compartment of rat lungs in situ decreased baseline liquid absorption and abrogated the stimulation of liquid absorption by the beta-adrenergic agonist terbutaline. There was no additional effect of Na_2S over that of the ENaC inhibitor amiloride. In electrophysiological Ussing chamber experiments with native lung epithelia (Xenopus laevis), Na_2S inhibited the stimulation of amiloride-sensitive current by terbutaline. beta-adrenergic agonists generally increase ENaC abundance by cAMP formation and activation of PKA. Activation of this pathway by forskolin and 3-isobutyl-1-methylxanthine increased amiloride-sensitive currents in H441 pulmonary epithelial cells. This effect was inhibited by Na_2S in a dose-dependent manner (5-50 muM). Na_2S had no effect on cellular ATP concentration, cAMP formation, and activation of PKA. By contrast, Na_2S prevented the cAMP-induced increase in ENaC activity in the apical membrane of H441 cells. H441 cells expressed the H_2S-generating enzymes cystathionine-3-syn-thase, cystathionine-gamma-lyase, and 3-mercaptopyruvate sulfurtrans-ferase, and they produced H_2S amounts within the employed concentration range. These data demonstrate that H_2S prevents the stimulation of ENaC by cAMP/PKA and, thereby, inhibits the proabsorptive effect of beta-adrenergic agonists on lung liquid clearance.