ARACHIDONIC-ACID MOBILIZATION IN P388D(1) MACROPHAGES IS CONTROLLED BY 2 DISTINCT CA2+-DEPENDENT PHOSPHOLIPASE A(2) ENZYMES

Macrophage-like P388D(1) cells mobilize arachidonic acid (AA) and produce prostaglandin E(2) upon stimulation with bacterial lipopolysaccharide and platelet-activating factor. We have now demonstrated that AA mobilization in these cells is composed of two distinct events: a transient phase in which AA accumulates in the cell and a sustained phase in which the fatty acid accumulates in the incubation medium. Both phases are markedly dependent on the presence of Ca2+ in the extracellular medium. Treatment with an antisense oligonucleotide to group II phospholipase A(2) inhibits the accumulation of AA in the incubation medium, but has no effect on the accumulation of this fatty acid in the cell. In addition, treatment with antisense oligonucleotide to group II phospholipase A(2) has no effect on the uptake of the esterification of AA. Collectively, these results indicate that, in addition to the previously demonstrated role of group II phospholipase A(2) in AA mobilization in activated P388D(1) cells, another phospholipase A(2), distinct from the group II enzyme, is implicated in raising the levels of intracellular AA during the early steps of P388D(1) cell activation and in modulating deacylation/reacylation reactions involving AA. The data suggest that each of the different phospholipase A(2) enzymes present in P388D(1) cells serves a distinct role in cell function.