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J. Biochem, 1992, Vol. 112, No. 6 756-761
© 1992 Japanese Biochemical Society

research-article

Preferential Activation of Phospholipase A2, by Low Concentrations of Phosphatidic Acid with Long-Chain Fatty Acids in Rabbit Platelets1

Takashi Sato2, Tsutomu Hashizume and Tatsuzo Fujii

Department of Biochemistry, Kyoto Pharmaceutical University Yamashina Kyoto, Kyoto 607

2To whom correspondence should be addressed

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 Ca2Plus;; 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.

1' This work waa supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Culture of Japan.


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