title: Preferential activation of phospholipase A2 by low concentrations of phosphatidic acid with long-chain fatty acids in rabbit platelets.
abstract: The role of phosphatidic acid (PA) in the signal transduction system of platelets was studied using 1-stearoyl 2-arachidonoyl PA (PASA). When PASA was added to rabbit platelets, aggregation occurred. BW755C, a dual inhibitor of cyclooxygenase and lipoxygenase, as well as p-bromophenacyl bromide and mepacrine, inhibitors of phospholipase A2, inhibited the aggregation induced by low concentrations of PASA, but not that induced by high concentrations. PASA also stimulated, in a dose-dependent manner, arachidonic acid liberation, lysophosphatidylcholine and diacylglycerol formation, and mobilization of intracellular Ca2+; all of which were dependent on the presence of Ca2+ in the outer medium. The arachidonic acid liberation was inhibited by p-bromophenacyl bromide or mepacrine, while diacylglycerol formation by low concentrations of PASA was inhibited by BW755C. With platelet membrane fractions or with the platelets made permeable to Ca2+ by pretreatment with ionomycin, PASA caused arachidonic acid liberation in the presence of Ca2+. Furthermore, PASA enhanced the activity of phospholipase A2 partially purified from platelet cytosol acting on 1-palmitoyl-2-[14C]arachidonoyl-glycerophosphoethanolamine. These results provide evidence that PASA preferentially potentiates the activation of phospholipase A2 in cooperation with Ca2+, suggesting that PA acts as a positive feedback regulator to potentiate the activation of phospholipase A2 and contributes to the amplification of platelet activation.
authors.affiliation: Department of Biochemistry, Kyoto Pharmaceutical University.
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.forename: T
authors.initials: T
authors.lastname: Hashizume
authors.forename: T
authors.initials: T
authors.lastname: Fujii
mesh_terms: D015772:4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyrazol-3-amine / Q000494:pharmacology; D000098:Acetophenones / Q000494:pharmacology; D000818:Animals; D001792:Blood Platelets / Q000201:enzymology*; D003600:Cytosol / Q000201:enzymology; D004789:Enzyme Activation; D007700:Kinetics; D010712:Phosphatidic Acids / Q000494:pharmacology*; D010741:Phospholipases A / Q000037:antagonists & inhibitors / Q000097:blood* / Q000302:isolation & purification; D054467:Phospholipases A2; D010974:Platelet Aggregation / Q000187:drug effects*; D011796:Quinacrine / Q000494:pharmacology; D011817:Rabbits
chemical_list: D000098:Acetophenones; D010712:Phosphatidic Acids; C060203:1-stearoyl-2-arachidonoylphosphatidic acid; D015772:4,5-Dihydro-1-(3-(trifluoromethyl)phenyl)-1H-pyrazol-3-amine; D010741:Phospholipases A; D054467:Phospholipases A2; D011796:Quinacrine; C006821:4-bromophenacyl bromide