Ultrastructure, in vitro, and in vivo functionality of platelet-like elements produced in the presence of SR1. (A) Platelet ultrastructure. (Upper) Representative microscopic fields of resting platelet populations examined by TEM. Bar, 2 µm. (Lower) Higher-magnification TEMs of native and culture-derived platelets. Bar, 1 µm. Culture-derived platelets exhibited similar ultrastructural characteristics to native platelets. (B) Flow-dependent thrombus formation. RAM.1-488–labeled native or culture-derived platelets mixed to hirudin-anticoagulated blood at a 1:100 ratio were perfused over immobilized type I collagen at 300 seconds−1 and observed in real time by DIC. (Upper) Individual labeled platelets (arrows) adhering to the matrix after 10 seconds of perfusion. (Lower) Platelet thrombi formed after 6 minutes of perfusion showing incorporation of labeled native and cultured platelets. Scale bars, 20 µm. (C) Laser-induced thrombosis model. Representative images of thrombi 2 minutes after laser injury of a mesenteric artery showing incorporation of RAM.1-488–labeled native or culture-derived platelets injected immediately after lesion. Scale bars, 20 µm. Bar graph, number of labeled platelets per thrombus (mean ± SEM of 4 experiments).
