Membrane tethers regulate platelet-matrix and platelet-platelet adhesive interactions. (A) (Left) Scanning electron microscopy of a single discoid platelet forming membrane tethers during adhesion to immobilized VWF (1800 s⁻¹). Note that tethers can be readily distinguished from filopodia in that the latter is inhibited by pretreating platelets with the actin polymerization inhibitor, cytochalasin D. (Right) Shear-dependent formation of adhesion contacts between discoid platelets involves the development of membrane tethers (arrows). (B) (Left) Reversible aggregation of discoid platelets. Note that in this image, all platelets cluster around a central activated platelet through the development of membrane tethers. (Right) The development of stable platelet aggregates is associated with classic platelet shape change characterized by sphering of the platelet body and the extension of multiple filopodial projections. (Modified from Brass et al⁶⁸ ; used with permission.) (This research was originally published in Maxwell et al.⁵⁹  and was adapted with permission. Platelets were imaged on a Hitachi S570 scanning electron microscope [Tokyo, Japan] at 20 kV accelerating voltage, 3 mm working distance.)