Involvement of calcium-independent phospholipase A(2) in uterine stromal cell phospholipid remodelling

The role of Ca2+-independent phospholipase A(2) (iPLA(2)) in arachidonic (A A) and docosahexaenoic (DHA) acid incorporation and phospholipid remodellin g in rat uterine stromal cells (U-III cells) was studied. Incorporation of AA and DHA into Um cell phospholipids was Ca2+-independent, Bromoenollacton e (BEL), a patent inhibitor of iPLA(2), reduced lysophosphatidylcholine lev el and AA incorporation into phospholipids by approximate to 20%. DHA incor poration was not affected by EEL, indicating that the pathways for AA and D HA incorporation are partially different. In control cells, the transfer of AA occurred mainly from diacyl-glycerophosphocholine (GroPCho) to alkenyla cyl-glycerophosphoethanolamine (GroPEtn) and to a lesser extent from diacyl -GroPCho to diacyl-GroPEtn. [H-3]DHA was redistributed from diacyl-GroPCho and alkylacyl-GroPEtn to alkenylacyl-GroPEtn, EEL treatment inhibited compl etely the redistribution of AA within diacyl-GroPCho and diacyl -GroPEtn an d reduced the [H-3]DHA content of diacyl-GroPEtn, indicating that a EEL-sen sitive iPLA(2) controls the redistribution of polyunsaturated fatty acids t o diacyl-GroPEtn. In contrast the redistribution of radioactive AA and DHA to alkenylacyl-GroPEtn was almost insensitive to EEL. The analysis of subst rate specificity and EEL sensitivity of iPLA(2) activity indicates that UII I cells exhibit at least two isoforms of iPLA(2), one of which is EEL-sensi tive and quite selective of diacyl species, and another one that is insensi tive to EEL and selective for alkenylacyl-GroPEtn. Taken together, these re sults suggest that several iPLA(2) participate independently in the remodel ling of Um cell phospholipids.