Scanning electron microscope study of platelet release by canine megakaryocytes in vitro.

Megakaryocytes were isolated from bone marrow from healthy dogs, using a combination of density-gradient centrifugation and polysucrose-velocity sedimentation techniques. The 2-step separation technique resulted in a preparation comprising 30% to 35% megakaryocytes of total nucleated cells. Accessibility to large numbers of viable canine megakaryocytes allowed investigation of platelet release by these cells in short-term cultures. Megakaryocytes were observed to form long cytoplasmic processes that gradually developed segmental constrictions and subsequently fragmented into platelet-sized pieces. Some platelet-sized cytoplasmic pieces of megakaryocytes presumably underwent discoid transformation.