ROLE OF PLA(2), PLC, AND PLD IN BRADYKININ-INDUCED RELEASE OF ARACHIDONIC-ACID IN MDCK CELLS

The role of cytosolic phospholipase A(2) (cPLA(2)), phosphatidylcholin e-specific phospholipase C (PC-PLC) and phospholipase D (PLD) in the b radykinin (BK)-stimulated release of arachidonic acid (AA) was examine d in Madin-Darby canine kidney (MDCK) cells. Release of AA, phosphoryl choline, choline, and phosphatidic acid (PA) or the transphosphatidyla tion product, phosphatidylethanol, was detected after 1 min of BK stim ulation. A role for PC-PLC was confirmed with D609, which reduced BK-s timulated AA by 70%. Ethanol (EtOH), which blunts PA formation, dimini shed BK-stimulated AA release by 50%. Together, D609 and EtOH inhibite d this release almost completely. Evidence indicated that diacylglycer ol and PA can enhance PLA(2) activity when added to cytosol extracts. The enzyme responsible for AA release was characterized as cPLA(2), si nce PLA(2) activity assayed in cell extracts was largely inhibited by an antibody to this enzyme. The membrane fraction PLA(2) activity incr eased significantly in BK-stimulated cells. We conclude that BK signal ing in MDCK cells is mediated by the lipid products of PC-PLC and PLD, increasing cPLA(2) activity, possibly by causing perturbations in the bilayer structure of its substrate, by a direct effect on the enzyme or by activation of protein kinases such as protein kinase C.