Studies on the mechanism for arachidonic acid liberation in mammalian cells with stimulus-response coupling

花生四烯酸是二十烷类化合物的前体，通过磷脂酶A2(PLA2)对膜磷脂的水解作用而释放出来。本研究旨在探讨二酰基甘油(DAG)脂肪酶在磷脂酶D(PLD)和磷脂酸磷酸水解酶(PAPase)的作用下释放花生四烯酸是否为刺激大鼠腹膜肥大细胞的重要途径。取得的结果如下：1.研究结果。通过加入乙醇抑制PLD激活产生的磷脂酸，或加入PAPase或DAG脂肪酶抑制剂，可抑制钙离子载体离子载体刺激下花生四烯酸的释放，抑制约50%。乙醇或上述抑制剂可完全抑制IgE受体依赖性刺激引起的花生四烯酸释放。大鼠腹膜肥大细胞中花生四烯酸的主要代谢产物前列腺素D_2(PGD_2)的产生可被乙醇或上述抑制剂完全抑制。在大鼠腹膜肥大细胞中，可特异性激活PLA2的蜂毒素可诱导花生四烯酸释放，但不能诱导花生四烯酸的产生，而引起PLD的ADP核糖化因子(ARF)刺激可诱导花生四烯酸的释放，而两者在乙醇存在下均被完全抑制。这些结果表明，在大鼠腹膜肥大细胞中，刺激诱导的花生四烯酸释放除PLA2途径外，还由PLD/PAPase/DAG脂肪酶途径参与，而花生四烯酸释放后PGD2的产生完全依赖于PLD连接的脂代谢。

Arachidonic acid as a precursor for eicosanoid is known to be liberated by the hydrolytic action of phospholipase A_2 (PLA_2) on membrane phospholipids. The present study has been undertaken to investigate whether or not the arachidonic acid liberation by diacylglycerol (DAG) lipase from DAG which is produced through the sequential actions of phospholipase D (PLD) and phosphatidate phosphohydrolase (PAPase), is the important pathway upon stimulation in rat peritoneal mast cells. The results obtained are as follows.1. The arachidonic acid liberation upon stimulation with Ca^<2+> ionophore ionomycin was inhibited by about 50 % by addition of ethanol to suppress phosphatidic acid production through PLD activation, or of inhibitors for PAPase or DAG lipase.2. The arachidonic acid liberation in response to IgE receptor-dependent stimulation was completely inhibited by ethanol or the inhibitors indicated above.3. The production of prostaglandin D_2 (PGD_2), a major metabolite of arachidonic acid in rat peritoneal mast cell in response to IgE receptor-dependent stimulation and also ionomycin, was completely suppressed by ethanol or the inhibitors indicated above.4. Stimulation with melittin, that can specifically activate PLA_2, induced arachidonic acid liberation but not PGD_2 production, while stimulation with ADP ribosylation factor (ARF), that does PLD,induced marked PGD_2 production as well as arachidonic acid liberation both of which were completely suppressed in the presence of ethanol.These results indicate that in rat peritoneal mast cells stimulus-induced arachidonic acid liberation is contributed by the sequential PLD/PAPase/DAG lipase pathway in addition to PLA_2 pathway, whereas PGD_2 production following arachidonic acid liberation is fully dependent on the PLD-linked lipid metabolism.