Hydrogen sulfide inhibits endothelial nitric oxide formation and receptor ligand-mediated Ca(2+) release in endothelial and smooth muscle cells.

BACKGROUND

In the vascular system, ATP-sensitive K(+)-channels are a target for H2S. Recent evidence suggests that H2S may also modulate Na(+)- and Ca(2+)-permeable channels and intracellular Ca(2+) stores, but the influence of H2S on endothelial Ca(2+) dynamics and Ca(2+)-dependent activation of endothelial nitric oxide synthase (eNOS) is unclear. In this study, we investigated the effects of H2S on Ca(2+) signaling in endothelial and smooth muscle cells with special emphasis given to the role of H2S in modulating endothelial NO formation.

METHODS

Experiments were performed with endothelial cells from porcine aorta, the human endothelial cell line HMEC-1, and smooth muscle cells from rat aorta and trachea. Mobilization of intracellular Ca(2+) and Ca(2+) entry was monitored with Fura-2. Activity of eNOS was determined as conversion of incorporated l-[(3)H]arginine into l-[(3)H]citrulline.

RESULTS

Incubation of endothelial cells with the H2S donors sodium hydrogen sulfide (NaHS) and GYY4137 blocked activation of eNOS by the receptor agonist ATP but not by the Ca(2+) ionophore A23187. Data revealed that H2S inhibited ATP-induced release of Ca(2+) from intracellular stores indicating that H2S attenuates eNOS activity by blocking capacitative Ca(2+) entry. A similar inhibitory effect of H2S on ATP-induced Ca(2+) release and Ca(2+) entry was also observed in human microvascular endothelial cells and smooth muscle cells.

CONCLUSIONS

H2S antagonized Ca(2+) mobilization by receptor agonists and store-operated Ca(2+) entry thereby limiting eNOS activation and NO formation. The effect of H2S on Ca(2+) stores was not restricted to endothelial cells but was also observed in vascular and tracheal smooth muscle cells.