P02 The impact of hydrogen sulfide on ion channels and transporters in airway epithelial cells

Abstract

Hydrogen sulfide (H2S) is emerging as an important regulator of numerous ion channels, particularly potassium channels. A growing body of evidence demonstrates the importance of potassium channel regulation by H2S for physiological processes such as smooth muscle relaxation. In the airways, H2S-induced smooth muscle relaxation leads to airway dilatation [1] . Aside from smooth muscle cells, epithelial cells are important for airway physiology. The ciliated airway epithelium is covered by a thin fluid layer (airway surface liquid, ASL) which allows effective ciliary beat and thereby mucociliary clearance. The volume and composition of the ASL is regulated by the vectorial transport of ions and, consequently, water across the epithelium. We questioned if H2S can be produced by airway epithelial cells and influences ion channels and transepithelial ion transport processes by those cells. RT-PCR and western blot experiments demonstrated the expression of H2S generating enzymes (cystathionine-γ-lyase and cystathionine-β-synthase) in human H441 airway epithelial cells. Furthermore, the measurement of H2S production by H441 lysates with the methylene blue method showed H2S generation which was inhibited by D,L-propargylglycine and aminooxyacetic acid. These data indicate that H441 airway epithelial cells have the capacity of H2S production. Transepithelial ion transport was electrophysiologically measured by Ussing chamber recordings on cultured human H441 airway epithelial cells at the air/liquid interface as well as tracheal preparations form pigs. In both models, exogenously applied H2S (by NaHS) decreased sodium absorption by ∼60% [2] . In H441 cells, this effect was dose-dependent (IC50 146 μM of NaHS) and fully reversible. There was no effect of H2S on amiloride-sensitive sodium channels which are located in the apical membrane of the epithelial cells. By contrast, there was a reduction in the activity of the basolaterally located Na+/K+-ATPase. The membrane abundance of the Na+/K+-ATPase, as determined by surface biotinylation and western blot, or cellular ATP concentrations were not affected by H2S. Furthermore, H2S also inhibited potassium channels in the basolateral membrane, the inhibition of which decreased Na+/K+-ATPase activity and overall sodium absorption by H441 cells. In sum, these data indicate that airway epithelial cells have the capacity of H2S production. Exogenously applied H2S decreases sodium absorption across airway epithelial cells by inhibiting the Na+/K+-ATPase as well as basolateral potassium channels. We conclude that H2S might represent a signaling molecule which affects ion transport processes across airway epithelial cells. However, the physiological regulation of ion transport by endogenously produced H2S remains to be determined. Supported by grants from the German Research Foundation AL1453/1–1 and AL1453/1–2.