Tether formation during platelet translocation on immobilized VWF.

Washed platelets (3 × 10⁸/mL) were perfused through microcapillary tubes coated with VWF (100 μg/mL) or isolated 39/34 kd fragment of VWF (A1 domain) (174 μg/mL) at 150 s⁻¹ as described in “Materials and methods.” (A) Digitized images of translocating platelets. VWF: During platelet translocation on immobilized VWF, 2 distinct behaviors were observed. Platelets either translocated continuously with no morphologic changes observed (left panels) or pulled fine membrane tethers (right panels). Tethers developed from specialized adhesion contacts (arrow) that did not move during tether formation. A1 domain: differential interference contrast microscopy (DIC) images of membrane tethers formed on isolated 39/34 kd fragment of VWF. (B) Scanning electron micrographs of platelet tethers. Tethers of varying lengths were pulled from the surface of translocating platelets (i-iii) and in some cases, platelets with 2 or more membrane protrusions were observed (iv-vi; see text for details). Multiple adhesion contact points (vi; white arrowheads) were also observed along the length of one tether, resulting in the generation of kinked tethers (Scale bar equals 1 μm). (C) Time-dependent change in tether length (μm) of 4 individual platelets.