Release of arachidonic acid from vascular endothelial cells: Fatty acyl specificity is observed with receptor-mediated agonists and with the calcium ionophore A23187 but not with melittin

Abstract

Vascular endothelial cells respond to a variety of physiological and pharmacological stimuli by releasing free arachidonic acid from membrane phospholipids, thus initiating synthesis of prostacyclin. Previous work in our laboratory has demonstrated that the thrombin-stimulated deacylation is specific for arachidonate and structurally similar polyunsaturated fatty acids that contain a delta-5 double bond. We now report that histamine, bradykinin, and the calcium ionophore A23187 exhibit the same fatty acid specificity as does thrombin. Experiments with both human umbilical vein and calf pulmonary artery endothelial cells indicate that these agonists stimulate the release of previously incorporated [¹⁴C]arachidonate but not 8,11,14-[¹⁴C]eicosatrienoate or [¹⁴C]docosatetraenoate. By contrast, melittin stimulates the release of 8,11,14-eicosatrienoate, docosatetraenoate, and oleate as well as arachidonate. These results suggest that histamine, bradykinin, and A23187 activate a common calcium-dependent phospholipase A₂. Melittin appears either to alter the substrate specificity of the receptor-linked phospholipase A₂ activity or to activate additional enzymes as well.