Dopheide Sacha M, Maxwell Mhairi J, Jackson Shaun P
Australian Centre for Blood Diseases, Department of Medicine, Monash Medical School, Box Hill, Victoria, Australia.
Blood. 2002 Jan 1;99(1):159-67. doi: 10.1182/blood.v99.1.159.
The adhesion and aggregation of platelets at sites of vascular injury is dependent on the initial binding of the GP Ib/V/IX receptor complex to immobilized von Willebrand factor (VWF). Under flow conditions, this interaction supports platelet translocation that is characteristically stop-start in nature. High resolution imaging of platelets during surface translocation on immobilized VWF revealed that thin membrane tethers (length: 0.91 microm-47.90 microm) were pulled from the surface of these cells. Membrane tethers were dynamic structures that extended from small, localized adhesion contacts under the influence of flow. Perfusion of platelets in the presence of blocking antibodies against integrin alpha(IIb)beta(3), or over isolated A1 domains, demonstrated that the VWF-GP Ib interaction was sufficient to induce membrane tether formation. The rate and extent of tether elongation was shear-dependent (shear range: 150 s(-1)-10,000 s(-1)), with mean tether length ranging from 3.23 microm to 16.55 microm, tether frequency from 2.67% to 97.33%, and tether growth rate from 0.04 microm/sec to 8.39 microm/sec. Tether formation and retraction did not require platelet activation; however, the growth rate, lifetime, and dimensions were significantly affected by the actin polymerization inhibitor, cytochalasin D, and by chelating intracellular calcium. Single-cell analysis revealed that formation of membrane tethers regulates the stop-start phases of platelet translocation on VWF, suggesting a potentially important role for this phenomenon in regulating the dynamics of the platelet-VWF interaction under flow.
血小板在血管损伤部位的黏附和聚集取决于糖蛋白Ib/V/IX受体复合物与固定化血管性血友病因子（VWF）的初始结合。在流动条件下，这种相互作用支持血小板移位，其特征是本质上的停停走走。对血小板在固定化VWF表面移位过程的高分辨率成像显示，从这些细胞表面拉出了薄的膜系链（长度：0.91微米至47.90微米）。膜系链是动态结构，在流动影响下从小的局部黏附接触处延伸出来。在存在针对整合素α(IIb)β(3)的阻断抗体的情况下灌注血小板，或在分离的A1结构域上灌注血小板，表明VWF-GP Ib相互作用足以诱导膜系链形成。系链伸长的速率和程度取决于剪切力（剪切力范围：150 s(-1)至10,000 s(-1)），平均系链长度范围为3.23微米至16.55微米，系链频率为2.67%至97.33%，系链生长速率为0.04微米/秒至8.39微米/秒。系链的形成和回缩不需要血小板激活；然而，生长速率、寿命和尺寸受到肌动蛋白聚合抑制剂细胞松弛素D以及螯合细胞内钙的显著影响。单细胞分析表明，膜系链的形成调节血小板在VWF上移位的停停走走阶段，表明这种现象在调节流动条件下血小板-VWF相互作用的动力学中可能具有重要作用。
