Boittin FX, Gribi F, Serir K, Bény JL. Ca 2ϩ -independent PLA2 controls endothelial store-operated Ca 2ϩ entry and vascular tone in intact aorta. Am J Physiol Heart Circ Physiol 295: H2466-H2474, 2008. First published October 24, 2008 doi:10.1152/ajpheart.00639.2008.-During an agonist stimulation of endothelial cells, the sustained Ca 2ϩ 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 Ca 2ϩ stores depletion to the opening of such channels are still elusive. We have used Ca 2ϩ and tension measurements in intact aortic strips to investigate the role of the Ca 2ϩ -independent isoform of phospholipase A 2 (iPLA2) in endothelial store-operated Ca 2ϩ entry and endothelium-dependent relaxation of smooth muscle. We provide evidence that iPLA2 is involved in the activation of endothelial store-operated Ca 2ϩ entry when Ca 2ϩ stores are artificially depleted. We also show that the sustained store-operated Ca 2ϩ 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 iPLA 2 metabolites arachidonic acid and lysophosphatidylcholine were found to stimulate Ca 2ϩ entry in native endothelial cells. However, only the latter triggered endothelium-dependent relaxation through NO release, suggesting that lysophosphatidylcholine produced by iPLA 2 upon Ca 2ϩ stores depletion may act as an intracellular messenger that stimulates store-operated Ca 2ϩ entry and subsequent NO production in endothelial cells. Finally, we found that ACh-induced endothelium relaxation also depends on iPLA 2 activation, suggesting that the iPLA2-dependent control of endothelial store-operated Ca 2ϩ entry is a key physiological mechanism regulating arterial tone. endothelial cells; calcium imaging; calcium-independent isoform of phospholipase A2; store-operated channels; endothelium-dependent relaxation IN A WIDE VARIETY of cells, agonists such as neurotransmitters, hormones, or growth factors trigger cellular responses through an increase of the cytosolic Ca 2ϩ concentration. This increase can result from both Ca 2ϩ release from intracellular Ca 2ϩ stores and Ca 2ϩ influx through plasma membrane channels. Many agonists trigger Ca 2ϩ release through the stimulation of phospholipase C, which involves the generation of inositol 1,4,5-trisphosphate [Ins(1,4,5)P 3 ] and diacylglycerol. The binding of Ins(1,4,5)P 3 to its receptor located on the endoplasmic reticulum triggers cytosolic Ca 2ϩ release, and the subsequent depletion of intracellular Ca 2ϩ stores activates Ca 2ϩ entry through store-operated channels. This phenomenon is called capacitative or store-operated Ca 2ϩ entry (28).A sustained phase of capacitive Ca 2ϩ entry through storeoperated channels following agonist-induced Ca 2ϩ release...

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