Michelson A D, Benoit S E, Kroll M H, Li J M, Rohrer M J, Kestin A S, Barnard M R
Department of Pediatrics, University of Massachusetts Medical School, Worcester 01655.
Blood. 1994 Jun 15;83(12):3562-73.
Thrombin decreases the platelet surface expression of the glycoprotein (GP) Ib-IX complex. To determine whether this effect is reversible, flow cytometric studies were performed with GPIb-IX-specific monoclonal antibodies. In both whole blood and washed platelet systems, incubation of platelets with thrombin or a combination of adenosine diphosphate and epinephrine resulted in a maximal decrease of the platelet surface expression of GPIb-IX within 5 minutes, after which there was a time-dependent return of the platelet surface GPIb-IX complex, which was maximal by 60 minutes. Exposure of the same platelets to additional exogenous thrombin resulted in a second decrease in platelet surface GPIb-IX, followed by a second reconstitution of platelet surface GPIb-IX. Throughout these experiments there was no measurable release from the platelets of glycocalicin (a proteolytic fragment of GPIb). Experiments in which platelets were preincubated with a biotinylated GPIb-specific MoAb showed that the GPIb molecules that returned to the platelet surface were the same molecules that had been translocated to the intraplatelet pool. The GPIb molecules that returned to the platelet surface were functionally competent to bind von Willebrand factor, as determined by ristocetin-induced platelet agglutination and ristocetin-induced binding of exogenous von Willebrand factor. Inhibitors of protein kinase C and myosin light-chain kinase enhanced the reexpression of platelet surface GPIb. In summary, the activation-induced decrease in the platelet surface expression of the GPIb-IX complex is reversible. Inactivation of protein kinase C and myosin light-chain kinase are important mechanisms in the reexpression of the platelet surface GPIb-IX complex.
凝血酶可降低血小板表面糖蛋白（GP）Ib-IX复合物的表达。为了确定这种作用是否可逆，我们使用GPIb-IX特异性单克隆抗体进行了流式细胞术研究。在全血和洗涤血小板系统中，血小板与凝血酶或二磷酸腺苷和肾上腺素的组合孵育会导致5分钟内血小板表面GPIb-IX的表达最大程度降低，此后血小板表面GPIb-IX复合物会出现时间依赖性恢复，60分钟时达到最大值。将相同的血小板暴露于额外的外源性凝血酶会导致血小板表面GPIb-IX再次降低，随后血小板表面GPIb-IX再次重建。在整个这些实验中，未检测到血小板释放出糖链蛋白（GPIb的蛋白水解片段）。用生物素化的GPIb特异性单克隆抗体对血小板进行预孵育的实验表明，回到血小板表面的GPIb分子与那些已转运至血小板内池的分子相同。通过瑞斯托霉素诱导的血小板凝集和瑞斯托霉素诱导的外源性血管性血友病因子结合测定，回到血小板表面的GPIb分子在功能上能够结合血管性血友病因子。蛋白激酶C和肌球蛋白轻链激酶的抑制剂可增强血小板表面GPIb的重新表达。总之，激活诱导的血小板表面GPIb-IX复合物表达降低是可逆的。蛋白激酶C和肌球蛋白轻链激酶的失活是血小板表面GPIb-IX复合物重新表达的重要机制。
