Comparison of shear or static conditions of MK deformations on a VWF-containing surface. Coverslips were removed from the flow chamber and rinsed with PBS before fixation in ice-cold methanol and subsequent Romanovsky staining (A-B, magnification ×500): during static 20-minute adhesion, cells displayed a spherical shape, without any proplatelet extension (A), but after exposure to high shear rate for 20 minutes, MKs extended long filopods at their tip and beaded platelet-like spikes were formed along the shaft (B). In separate experiments, images were recorded on coverslips coated with VWF (C-D) or on stimulated HUVECs (E-F) during real-time perfusion. Panel C shows proplatelet formation during 16 hours on VWF-coated slides in static conditions extending in different directions (C). In shear conditions, after 20 minutes, proplatelet formation is bipolar and organized along the flow (D). Similar organization of proplatelet formation is seen on UL-VWF released by HUVECs stimulated by IBMX and forskolin (E-F). Bars on panels C through F represent 10 μm.