MK deformation on a VWF surface at high shear rate. Cells suspended in IMDM were perfused on VWF at 1800 s−1 for 10 minutes; then IMDM alone was perfused for 10 minutes. Adhesion led to major cell shape changes and to proplatelet formation. Microphotographs during perfusion indicate 4 different stages starting from undeformed MKs (stage 1) to early deformation characterized by loss of cell sphericity (stage 2); stage 3 includes later deformation of MKs with cytoskeletal reorganization at a cell pole or both ends, also a long thin filament of successive “beads on a thread”; stage 4 comprises fragmentation of proplatelets and cleavage from the nucleus, as well as platelet formation and release. Proportion of cells relative to the total number of cells counted in 10 fields was plotted as a function of perfusion time classified according to these 4 stages for cord blood MKs (bottom left panel) or bone marrow MKs (bottom right panel) perfused on VWF. Photographs are representative of 15 experiments, curves are mean (± SEM) of 8 experiments. The bar represents 10 μm. Black lines have been inserted to indicate repositioned images.
