Institut des Vaisseaux et du Sang, Service d'Hématologie and INSERM U348, Hopital Lariboisiere, 8 rue Guy Patin, Paris, 75010, France.
Platelets. 1995;6(2):91-8. doi: 10.3109/09537109509078449.
The effects on platelet activation of two different tetrapeptides, KRDS present on human lactotransferrin and RGDS present on adhesive proteins such as human fibrinogen α-chain, were compared by a combination of morphological and functional techniques. Ultrastructural observations of α-thrombin stimulated platelets (0.05 U/ml), show strong platelet aggregation and full α-granule release. In the presence of RGDS (0.1-1 mM) aggregation was impaired but secretion was not blocked and platelets had released their α-granule contents. Platelets appeared uniformly degranulated with a dense central meshwork of microfilaments. In the presence of KRDS (0.5-1 mM), the platelets were activated with shape change and pseudopod formation. Aggregation was also impaired, but to a lesser extent since RGDS is active at a concentration as low as 0.1 mM, and, in contrast to RGDS, secretion was severely reduced. Electron microscopy showed that numerous α-granules were still scattered in the cytoplasmic matrix or often gathered in the centre of the platelet, but the majority of the open canalicular system cisternae remained clear. An immunoelectron microscopic study using immunogold and monospecific antibodies directed against fibrinogen and the a-granule membrane protein P-selectin (GMP 140) was performed. In the presence of RGDS, fibrinogen was released and P-selectin was translocated to the platelet surface; in contrast, in the presence of KRDS, fibrinogen remained localized in the α-granule, and the P-selectin associated with the a-granule. These observations were accompanied by some functional results: thrombin-induced platelet aggregation was inhibited by both peptides, and in contrast to RGDS, secretion was severely reduced in the presence of KRDS: serotonin release from dense granule was reduced by 73% compared to the control. These results show that these two tetrapeptides, in spite of some structural similarities, act differently in impairing platelet function. KRDS interfering with both the dense and α-granule release reaction may be a useful tool for a better understanding of the platelet secretion mechanism.
通过形态学和功能技术的结合，比较了两种不同的四肽对血小板激活的影响，一种是存在于人乳转铁蛋白上的 KRDS，另一种是存在于纤维蛋白原α链等黏附蛋白上的 RGDS。观察 0.05U/ml α-凝血酶刺激的血小板的超微结构，显示出强烈的血小板聚集和完全的α-颗粒释放。在 RGDS（0.1-1mM）存在下，聚集受到损害，但分泌没有被阻断，血小板释放了它们的α-颗粒内容物。血小板看起来均匀脱颗粒，中央有密集的微丝网格。在 KRDS（0.5-1mM）存在下，血小板发生形态改变和伪足形成而被激活。聚集也受到损害，但程度较轻，因为 RGDS 在 0.1mM 的浓度下就很活跃，而且与 RGDS 相反，分泌严重减少。电子显微镜显示，许多α-颗粒仍散在细胞质基质中，或经常聚集在血小板中心，但大多数开放小管系统小泡仍然清晰。使用针对纤维蛋白原和α-颗粒膜蛋白 P-选择素（GMP140）的免疫金和单特异性抗体进行免疫电镜研究。在 RGDS 存在下，纤维蛋白原被释放，P-选择素被转位到血小板表面；相反，在 KRDS 存在下，纤维蛋白原仍然局限在α-颗粒中，与α-颗粒相关的 P-选择素。这些观察结果伴随着一些功能结果：两种肽都抑制了凝血酶诱导的血小板聚集，与 RGDS 相反，KRDS 存在时严重减少了分泌：与对照相比，致密颗粒中的 5-羟色胺释放减少了 73%。这些结果表明，尽管这两种四肽有一些结构上的相似之处，但在损害血小板功能方面作用不同。KRDS 干扰致密颗粒和α-颗粒释放反应，可能是更好地理解血小板分泌机制的有用工具。
