Nilsson Ulrika K, Svensson Samuel P S, Grenegård Magnus
Division of Pharmacology, Department of Medicine and Care, Faculty of Health Sciences, Linköpings Universitet, SE-581 85 Linköping, Sweden.
Haematologica. 2002 Jul;87(7):730-9; discussion 739.
Platelet reactivity is regulated by various important bioactive and physiologic substances. The objective of this study was to characterize lysophosphatidic acid (LPA)-triggered responses in human platelets. In addition, the effect of LPA was compared with that of other activators and possible synergistic interactions were evaluated.
LPA-triggered cytosolic Ca(2+) responses were measured using fura-2-loaded platelets in a spectrofluorometer. Furthermore, platelet aggregation and secretion were analyzed in a lumi-aggregometer and protein tyrosine phosphorylation was detected with the Western blot technique.
LPA dose-dependently increased cytosolic Ca(2+) concentration (Ca(2+)) in platelets. This response involved both influx of extracellular Ca(2+) and release of Ca(2+) from intracellular stores. However, in comparison with other platelet agonists, i.e. thrombin and adenosine 5'-diphosphate (ADP), LPA was a very weak Ca(2+)-elevating agent. Furthermore, we observed that the LPA-induced rise in Ca(2+) was markedly suppressed by cyclic nucleotide-elevating agents. In functional studies, LPA failed to stimulate platelet aggregation and secretion. However, in combination with adrenaline, another weak platelet agonist, LPA could induce an irreversible and complete aggregatory response. There was an individual variation in aggregatory response and tyrosine phosphorylation when LPA and adrenaline were combined. These agents induced a powerful response on platelets from some individuals, but had a weak or no effect on others.
The present study shows, for the first time, that isolated platelets from some healthy blood donors respond synergistically to a combination of LPA and adrenaline. Platelet activation is a key step in distinguishing normal hemostasis from pathologic hemostasis. Increased knowledge about this mechanism might help to predict individual responses and provide new insights into molecular mechanisms responsible for pathologic thrombosis.
血小板反应性受多种重要生物活性和生理物质调节。本研究的目的是表征溶血磷脂酸（LPA）触发的人血小板反应。此外，将LPA的作用与其他激活剂的作用进行比较，并评估可能的协同相互作用。
使用在荧光分光光度计中加载fura-2的血小板测量LPA触发的胞质Ca(2+)反应。此外，在光聚集仪中分析血小板聚集和分泌，并用蛋白质印迹技术检测蛋白质酪氨酸磷酸化。
LPA剂量依赖性地增加血小板中的胞质Ca(2+)浓度（[Ca(2+)]i）。该反应涉及细胞外Ca(2+)的流入和细胞内储存的Ca(2+)释放。然而，与其他血小板激动剂，即凝血酶和腺苷5'-二磷酸（ADP）相比，LPA是一种非常弱的Ca(2+)升高剂。此外，我们观察到环核苷酸升高剂可显著抑制LPA诱导的[Ca(2+)]i升高。在功能研究中，LPA未能刺激血小板聚集和分泌。然而，与另一种弱血小板激动剂肾上腺素联合使用时，LPA可诱导不可逆的完全聚集反应。LPA和肾上腺素联合使用时，聚集反应和酪氨酸磷酸化存在个体差异。这些药物对一些个体的血小板产生强烈反应，但对另一些个体则作用微弱或无作用。
本研究首次表明，来自一些健康献血者的分离血小板对LPA和肾上腺素的组合有协同反应。血小板活化是区分正常止血和病理性止血的关键步骤。对这一机制的更多了解可能有助于预测个体反应，并为病理性血栓形成的分子机制提供新的见解。
