Background and Objectives Endothelial cells are active participants in inflammatory processes. They are involved in diverse activities including the regulation of leucocyte extravasation, angiogenesis, cytokine production, protease and extracellular matrix synthesis, vasodilation, etc. The small gaseous molecule hydrogen sulphide (H2S) is involved in a variety of physiological processes like vascular relaxation, angiogenesis, neurotransmission and inflammation. In the vascular system, ATP-sensitive K+-channels are a major target for H2S but over the last few years evidence has accumulated that several Na+- and Ca2+-permeable channels are also sensitive to H2S. In the present study we investigated the effect of H2S on Ca2+ signalling in cultured endothelial and smooth muscle cells with special emphasis given to the role of H2S in modulating store-operated Ca2+ channels.
Materials and Methods Experiments were performed with human microvascular endothelial cells (HMEC-1), endothelial cells isolated from porcine aorta, and smooth muscle cells isolated from rat aorta and rat trachea. Mobilisation of intracellular Ca2+ and Ca2+ entry was monitored by measuring the intracellular free Ca2+ concentration with FURA-2 in the absence and presence extracellular Ca2+, respectively. Activity of endothelial nitric oxide synthase (eNOS) in intact cells was determined as conversion of incorporated L-[3H]-arginine into L-[3H]-citrulline.
Results Incubation of human and porcine endothelial cells with the H2S-donor NaHS (100 µM, 10–45 min) evoked a release of Ca2+ from intracellular stores that was not accompanied by Ca2+ influx from the extracellular space. In accordance with these data suggesting that H2S may inhibit store-operated Ca2+ entry, incubation of cells with NaHS attenuated Ca2+ influx induced by depletion of Ca2+ stores with receptor agonists (ATP, histamine) or the endoplasmatic reticulase ATPase inhibitor, thapsigargin. As a consequence, the stimulatory effect of these agonists on endothelial NO formation was strongly diminished, whereas the response to the Ca2+ ionophore A23187 was barely affected. Similar to the results obtained with endothelial cells, depletion of intracellular Ca2+ stores in smooth cells isolated from rat aorta or rat trachea also resulted in a pronounced Ca2+ entry that was completely blocked upon pre-treatment of cells with NaHS.
Conclusions H2S inhibits the stimulatory effect of Ca2+ of mobilising agonists on endothelial NO formation by attenuating store-operated Ca2+ entry. Inhibition of store-operated Ca2+ channels by H2S is not peculiarity of endothelial cells but also occurs in vascular and tracheal smooth muscle cells. These hitherto undescribed effects may be in part possible for the beneficial effects of H2S in sulphur bath therapy.
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