Hydrogen sulfide inhibits endothelial nitric oxide formation and receptor ligand-mediated Ca2+ 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 Ca2+-permeable channels and intracellular Ca2+ stores, but the influence of H2S on endothelial Ca2+ dynamics and Ca2+-dependent activation of endothelial nitric oxide synthase (eNOS) is unclear. In this study, we investigated the effects of H2S on Ca2+ 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 Ca2+ and Ca2+ entry was monitored with Fura-2. Activity of eNOS was determined as conversion of incorporated L-[H-3]arginine into L-[H-3]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 Ca2+ ionophore A23187. Data revealed that H2S inhibited ATP-induced release of Ca2+ from intracellular stores indicating that H2S attenuates eNOS activity by blocking capacitative Ca2+ entry. A similar inhibitory effect of H2S on ATP induced Ca2+ release and Ca2+ entry was also observed in human microvascular endothelial cells and smooth muscle cells. Conclusions: H2S antagonized Ca2+ mobilization by receptor agonists and store-operated Ca2+ entry thereby limiting eNOS activation and NO formation. The effect of H2S on Ca2+ stores was not restricted to endothelial cells but was also observed in vascular and tracheal smooth muscle cells. (c) 2015 Institute of Pharmacology, Polish Academy of Sciences. Published by Elsevier Sp. z o.o. All rights reserved.