Megakaryocytes produce microparticles via an active, constitutive process. (A) Video-enhanced differential-interference contrast microscopy showing 2 examples of a mouse megakaryocyte forming microparticles in vitro. Small vesicles in linear arrays were observed extending from the surface of megakaryocytes. The microparticle at the tip of this process is 0.5 μm (). Scale bar represents 1 μm. (B) Surface blebs were visualized in unstained, living mouse megakaryocytes imaged by the RTM-3 in light modality using a 100× objective lens. This representative frame shows a membrane region that exhibited active surface blebbing. Scale bar represents 1 μm. (C) Thin-section electron micrograph showing the surface of a mouse megakaryocyte. Numerous small projections were observed emanating from the surface. The width of this field is 4 μm. (D) Thin-section electron micrographs showing blebs at various stages along the surface of a mouse megakaryocyte. The surface projections are approximately 300 nm in diameter.