Questions:

Na⁺ absorption by lung epithelia is essential for the maintenance of pulmonary fluid homeostasis. Recently, there is a growing body of evidence that the gasotransmitter H₂S plays an important role in the regulation of Na⁺ absorption. In previous studies we showed that exogenously applied H₂S decreases pulmonary Na⁺ absorption by inhibiting the Na⁺/K⁺-ATPase. However, whether or not endogenously produced H₂S regulates Na⁺ transport remains unknown. The aim of this study was to investigate possible effects of endogenously produced H₂S on Na⁺ transport by pulmonary epithelial cells.

Methods:

The expression of H₂S-generating enzymes, cystathionine-β-synthase (CBS) and cystathionine-γ-lyase (CTH) in H441 lung epithelial cells was investigated by RT-PCR and western blot. To investigate putative effects of endogenous H₂S on Na⁺ transport, cultured H441 monolayers were incubated for 24h with an inhibitor of CBS (aminooxyacetic acid, AOA, 0.5 and 5mM), an inhibitor of CTH (DL-propagylglycine, PPG, 0.5 and 5 mM) or L-cysteine (10 mM), the substrate for CBS/CTH. After incubation, amiloride-sensitive currents (I_ami) which represent Na⁺ transport were estimated in Ussing chamber experiments.

Results:

Both H₂S-generating enzymes, CBS and CTH, were expressed in H441 cells. Inhibition of CTH with PPG significantly increased I_ami by 22%. There was no such effect by inhibiting CBS with AOA. By contrast, a stimulation of CBS/CTH with L-cysteine significantly decreases I_ami by 21%.

Conclusion:

Stimulation and inhibition of H₂S-generating enzymes led to changes in amiloride-sensitive Na⁺ transport by H441 cells. These data suggest that endogenous H₂S plays a role in long-term regulation of pulmonary Na⁺ transport.