Esterification of 8,11,14-eicosatrienoate and arachidonate into alkylacyl- and diacylglycerophosphocholine by vascular endothelial cells

Agonist-stimulated phospholipases release arachidonate, but not 8,11,14-eicosatrienoate, from human endothelial cells. One source of the arachidonic acid is deacylation of 1-alkyl-2-arachidonoyl-glycerophosphocholine, with subsequent conversion of some of the resultant lysophospholipid to platelet-activating factor. This study has compared the distribution of incorporated 8,11,14-¹⁴C]-eicosatrienoate in alkylacyl-GPC and diacyl-GPC with that of ¹⁴C]arachidonate synthesized endogenously by desaturation of the 8,11,14-¹⁴C]eicosatrienoate. Cells were incubated for 24 or 48 hr with 8,11,14-¹⁴C]eicosatrienoate, and the resultant mixture of¹⁴C-fatty acids in the cellular lipids was characterized by gas chromatography. The choline phospholipids were then separated, hydrolyzed with phospholipase C and derivatized to diradylbenzoates. Gas chromatographic analysis indicated extensive incorporation of ¹⁴C]eicosatrienoate, as well as ¹⁴C]arachidonate, into alkylacyl-GPC. Although the ratio of esterified ¹⁴C]arachidonate to ¹⁴C]eicosatrienoate was greater in alkylacyl-GPC than in diacyl-GPC, the enrichment with ¹⁴C]arachidonate was far less than the ratio of arachidonate/eicosatrienoate released from these cells. These results thus support the hypothesis that the acyl specificity of polyunsaturated fatty acid release is provided by the agonist-stimulated phospholipase A₂ rather than the composition of the alkylacyl-GPC.