ROLE OF SERINE ESTERASE IN A23187-MEDIATED ACTIVATION OF PHOSPHOLIPASE-A2 IN PULMONARY ENDOTHELIUM

To test the hypothesis that an endothelial cell membrane-associated se rine esterase is involved in regulating phospholipase A2 (PLA2), we st udied the effect of the calcium ionophore A23187 on intracellular PLA2 activity and arachidonic acid (AA) release in bovine pulmonary arteri al endothelial cells. Exposure of these cells to A23187 causes a conce ntration-dependent increase in PLA2 activity and [C-14]AA release. In addition to increasing PLA2 activity and AA release, A23187 enhances t he activity of endothelial cell membrane-associated serine esterase th at acts on the synthetic substrate Nalpha-p-tosyl-L-arginine methyl es ter. Serine esterase inhibitors, such as phenylmethylsulfonyl fluoride and diisopropyl fluorophosphate, prevent the A23187-mediated increase in serine esterase activity, PLA2 activity, and AA release. Pretreatm ent of the cells with actinomycin D or cycloheximide does not prevent the A23187-mediated increase in AA release, serine esterase activity, or PLA2 activity. The membrane-associated serine esterase activity dir ectly correlates with membrane PLA2 activity. These results suggest th at a membrane-associated serine esterase plays a pivotal role in regul ating PLA2 activity after exposure to A23187.