Departments of Laboratory Medicine and Pathology, Pediatrics, University of Minnesota Medical School, UMHC Box 490, 420 Delaware Street S.E., Minneapolis, MN, 55455, USA.
Platelets. 1996;7(5-6):321-8. doi: 10.3109/09537109609023595.
The present study has used washed human platelets combined with ethylene diamine tetracetic acid (EDTA) to determine the influence of calcium ions on thrombin-induced down-regulation of glycoprotein (GP) Ib/IX, the platelet surface receptor for von Willebrand factor (vWF). Bovine plasma vWF (BvWF) does not require the antibiotic, ristocetin, or calcium ions to cause agglutination of platelets. Thus, EDTA platelets agglutinate as well with BvWF as platelets in the absence of the chelating agent. Thrombin treatment of EDTA platelets prevented subsequent agglutination by BvWF. However, the addition of calcium ions to the sample restores sensitivity of the six PIb/IX receptors, and irreversible agglutination occurs when BvWF is added. Monoclonal antibodies to GPIb/IX and GPIIb/IIIa demonstrated that restoration of refractory platelet sensitivity to BvWF was related to GPIb/IX, not to GPIIb/IIIa. Experimental results suggest that GPIb/IX receptors on thrombin-treated EDTA platelets can be down-regulated by thrombin, but are not cleared from the surface to internal membranes.
本研究使用洗涤后的人血小板与乙二胺四乙酸（EDTA）结合，以确定钙离子对凝血酶诱导的血小板表面受体 von Willebrand 因子（vWF）受体糖蛋白（GP）Ib/IX 下调的影响。牛血浆 vWF（BvWF）不需要抗生素、立托司汀或钙离子引起血小板聚集。因此，EDTA 血小板与 BvWF 一样容易聚集，而不存在螯合剂。凝血酶处理 EDTA 血小板可防止随后被 BvWF 聚集。然而，向样品中添加钙离子可恢复对六 PIb/IX 受体的敏感性，当添加 BvWF 时会发生不可逆聚集。针对 GPIb/IX 和 GPIIb/IIIa 的单克隆抗体表明，恢复对 BvWF 的抗血小板敏感性与 GPIb/IX 有关，而与 GPIIb/IIIa 无关。实验结果表明，凝血酶处理的 EDTA 血小板上的 GPIb/IX 受体可被凝血酶下调，但不会从表面清除到内膜。
