Ether phospholipids in control and 20:4-depleted rat PMN: additional evidence for a 1-O-alkyl-2-20:4-sn-glycerol-3-phosphocholine specific phospholipase A2.

Earlier studies from out laboratory have shown that PAF and LTB4 biosynthesis are inhibited in rat PMN depleted of its 20:4 (JBC. '86, 261, 7592). To test whether these cells contain sufficient 1-O-alkyl-2-acyl-GPC to support PAF synthesis, phosphotidyl choline was isolated from these 20:4-depleted cells, fractionated into different subclasses and their fatty acid composition determined. These results were compared with those obtained with control PMN. Both control and 20:4-depleted PMN contained significantly large amounts of alkylacyl-GPC and diacyl-GPC. Small amounts (4%) of alkenyl-acyl-GPC were also present. The amount of 20:3 in 20:4-depleted cells was more or less equal to the amount of 20:4 in control cells. About 62% of PC-bond 20:4 in control PMN and about 56% of PC-bound 20:3 in the 20:4-depleted PMN was found associated with the alkylacyl species. These results show that both control and 20:4 depleted PMN have ample precursor substrates to support PAF biosynthesis and these substrates are enriched with 20:4 in control cells and with 20:3 in 20:4-depleted cells. These findings are consistant with the existance of a highly specific phospholipase A2 capable of distinguising 20:4 from 20:3 containing phospholipids.