Kaya H, Patton G M, Hong S L
Department of Medicine, New England Deaconess Hospital, Boston, Massachusetts 02215.
J Biol Chem. 1989 Mar 25;264(9):4972-7.
This study evaluates the role of phosphatidylinositol 4,5-bisphosphate (PIP2) and its metabolites as possible mediators in the activation of phospholipases A2 in porcine aortic endothelial cells. We compared the time courses of bradykinin-induced turnover of phosphoinositides and the appearance of unesterified arachidonic acid (uAA) and eicosanoids. The metabolism of phosphoinositides was examined in cells prelabeled with [3H]inositol, which has a similar distribution as the endogenous inositol lipids. At 37 degrees C, bradykinin induced a rapid rise in lysophosphatidylinositol (lyso-PI) and inositol 1,4,5-trisphosphate (IP3) as well as a decrease in PIP2. Lyso-PI formation was detected at 10 s, as early as PIP2 degradation and IP3 formation. This suggests that the activation of PIP2-hydrolyzing phospholipase C and PI-hydrolyzing phospholipase A2 are simultaneous. However, at 30 degrees C, lyso-PI formation was detected in the absence of an increase in IP3 indicating that the activation of phospholipase A2 does not require the accumulation of IP3. The time course of formation of uAA and eicosanoids were examined in [3H]arachidonic acid-prelabeled cells. The 3H radioactivity was distributed among the phospholipid classes and subclasses the same as the endogenous phospholipids. Bradykinin stimulated the intracellular accumulation of uAA, detectable at 5 s, earlier than that of 1,2-diacylglycerol and phosphatidic acid. Such immediate formation of uAA further supports the notion that activation of phospholipase A2 is a very early event during the interaction of bradykinin with porcine endothelial cells, and that PIP2 hydrolysis is not prerequisite for the initial activation of phospholipase A2.
本研究评估磷脂酰肌醇4,5 - 二磷酸（PIP2）及其代谢产物作为猪主动脉内皮细胞中磷脂酶A2激活可能的介质的作用。我们比较了缓激肽诱导的磷酸肌醇周转以及未酯化花生四烯酸（uAA）和类花生酸出现的时间进程。在用[3H]肌醇预标记的细胞中检测磷酸肌醇的代谢，[3H]肌醇与内源性肌醇脂质具有相似的分布。在37℃时，缓激肽诱导溶血磷脂酰肌醇（lyso - PI）和肌醇1,4,5 - 三磷酸（IP3）迅速增加以及PIP2减少。在10秒时检测到lyso - PI形成，与PIP2降解和IP3形成一样早。这表明水解PIP2的磷脂酶C和水解PI的磷脂酶A2的激活是同时发生的。然而，在30℃时，在IP3没有增加的情况下检测到lyso - PI形成，表明磷脂酶A2的激活不需要IP3的积累。在用[3H]花生四烯酸预标记的细胞中检查uAA和类花生酸形成的时间进程。3H放射性在磷脂类别和亚类中的分布与内源性磷脂相同。缓激肽刺激uAA的细胞内积累，在5秒时可检测到，比1,2 - 二酰基甘油和磷脂酸更早。uAA的这种即时形成进一步支持了以下观点，即磷脂酶A2的激活是缓激肽与猪内皮细胞相互作用期间的一个非常早期的事件，并且PIP2水解不是磷脂酶A2初始激活的先决条件。
