Velardo B, Lagarde M
Biochem Biophys Res Commun. 1985 Aug 15;130(3):1109-14. doi: 10.1016/0006-291x(85)91730-9.
The oxygenation of arachidonic acid into thromboxane B2 (TXB2), 12-hydroxy-heptadecatrienoic (HHT) and 12-hydroxy-eicosatetraenoic (12-HETE) acids has been examined in human platelets in the absence or presence of 1mM calcium. From endogenous arachidonic acid, external calcium did not affect the formation of cyclo-oxygenase products (TXB2 and HHT) but enhanced that of 12-HETE when thrombin at high concentrations was the agonist. Dose-response curves performed with thrombin and collagen revealed that increased stimulation resulted in higher ratios of 12-HETE/HHT. On the other hand external calcium did not alter significantly the synthesis of either products from exogenous arachidonic acid and the total conversion of the substrate was unchanged. We conclude that extracellular calcium may facilitate the liberation of arachidonic acid from platelet phospholipids when induced by high thrombin concentrations. The excess of arachidonic acid liberated would then be diverted towards the lipoxygenase pathway.
在不存在或存在1mM钙的情况下，已对人血小板中花生四烯酸氧化生成血栓素B2（TXB2）、12-羟基-十七碳三烯酸（HHT）和12-羟基-二十碳四烯酸（12-HETE）的情况进行了研究。对于内源性花生四烯酸，外部钙不影响环氧化酶产物（TXB2和HHT）的形成，但当高浓度凝血酶作为激动剂时，会增强12-HETE的生成。用凝血酶和胶原蛋白进行的剂量反应曲线显示，刺激增加会导致12-HETE/HHT的比率升高。另一方面，外部钙对外源性花生四烯酸生成的任何一种产物的合成均无显著影响，且底物的总转化率不变。我们得出结论，当受到高浓度凝血酶诱导时，细胞外钙可能促进花生四烯酸从血小板磷脂中释放出来。然后，释放出的过量花生四烯酸将转向脂氧合酶途径。
