1-1-diethyl-2-hydroxy-2-nitrosohydrazine and arachidonyltrifluoromethane

During an agonist stimulation of endothelial cells, the sustained Ca2+ entry occurring through store-operated channels has been shown to significantly contribute to smooth muscle relaxation through the release of relaxing factors such as nitric oxide (NO). However, the mechanisms linking Ca2+ stores depletion to the opening of such channels are still elusive. We have used Ca2+ and tension measurements in intact aortic strips to investigate the role of the Ca2+-independent isoform of phospholipase A2 (iPLA2) in endothelial store-operated Ca2+ entry and endothelium-dependent relaxation of smooth muscle. We provide evidence that iPLA2 is involved in the activation of endothelial store-operated Ca2+ entry when Ca2+ stores are artificially depleted. We also show that the sustained store-operated Ca2+ entry occurring during physiological stimulation of endothelial cells with the circulating hormone ATP is due to iPLA2 activation and significantly contributes to the amplitude and duration of ATP-induced endothelium-dependent relaxation. Consistently, both iPLA2 metabolites arachidonic acid and lysophosphatidylcholine were found to stimulate Ca2+ entry in native endothelial cells. However, only the latter triggered endothelium-dependent relaxation through NO release, suggesting that lysophosphatidylcholine produced by iPLA2 upon Ca2+ stores depletion may act as an intracellular messenger that stimulates store-operated Ca2+ entry and subsequent NO production in endothelial cells. Finally, we found that ACh-induced endothelium relaxation also depends on iPLA2 activation, suggesting that the iPLA2-dependent control of endothelial store-operated Ca2+ entry is a key physiological mechanism regulating arterial tone.

Topics: Acetylcholine; Adenosine Triphosphate; Animals; Aorta, Thoracic; Arachidonic Acid; Arachidonic Acids; Calcium Channels; Calcium Signaling; Cells, Cultured; Endothelium, Vascular; Enzyme Inhibitors; Group VI Phospholipases A2; Hydrazines; Lysophosphatidylcholines; Male; Mice; Mice, Inbred C57BL; Muscle, Smooth, Vascular; Nitric Oxide; Nitric Oxide Donors; Nitric Oxide Synthase Type III; Vasodilation; Vasodilator Agents