Regulation of arachidonic acid release by calcium influx in human endothelial cells

In response to stimuli, endothelial cells release arachidonic acid, a lipid precursor of various vasoactive substances. We have investigated the relat ionships between cytosolic Ca2+ movements and arachidonic acid release in h uman umbilical vein endothelial cells. Histamine, a receptor-dependent agon ist, and thapsigargin, a specific inhibitor of sarco-/endoplasmic Ca2+ pump s, time- and dose-dependently increased the release of [1-C-14]-arachidonic acid. This release was inhibited by AACOCF(3), a selective inhibitor of cy tosolic phospholipase A(2) (PLA(2)). In the absence of Ca2+ influx, arachid onic acid release was suppressed in both histamine- and thapsigargin-stimul ated cells, despite marked elevations of cytosolic Ca2+ concentration ([Ca2 +](i)). In the presence of Ca2+ influx, arachidonic acid release was reduce d in cells treated with BAPTA, an intracellular Ca2+ buffer, or with SK&F 9 6365, a receptor-operated Ca2+ channel blocker. Arachidonic acid release wa s analyzed as a function of the two successive phases of Ca2+ response to s timulation: Ca2+ peak and plateau phase, reflecting Ca2+ mobilization from internal stores and Ca2+ influx, respectively. The amount of arachidonic ac id released was directly related to [Ca2+](i) values measured at the influx phase with a 80 nM [Ca2+](i) threshold, similar to that reported for PLA(2 ) translocation. This suggests that Ca2+ entry from the extracellular space is essential for activating cytosolic PLA(2) in human endothelial cells.