Characterization of fibrin microparticles.

(A) Size distribution of fibrin microparticles. Microparticles were prepared from thrombin-cleaved plasma, homogenized, and sedimented as described in “Materials and methods.” The size distribution of the suspended microparticles was analyzed using a ZM Coulter counter; the sizes were 1.5-3.25 μm, 3.25-4.05 μm, and >4.05 μm in columns A, B, and C, respectively. (B) Fibrin cross-linking of microparticles. Fibrinogen (lane 1), parent plasma clots (lane 2), and fibrin microparticles derived by homogenization and sedimentation (lane 3) were solubilized in urea and analyzed under reduced conditions on 10% SDS-PAGE. The gels were stained with Coomassie blue dye. The migration of the α-chain polymers, γ-γ dimers, and β chains is shown. The molecular weight markers are shown to the right. (C) Autoradiogram of ¹²⁵I-fibrin incorporated into plasma clots. ¹²⁵I-fibrinogen was added to plasma supplemented with unlabeled fibrinogen and clotted with thrombin, and the microparticles were prepared. The parent clot and the final microparticles were analyzed as in panel B, followed by autoradiography; the microparticles are depicted in lane 1; parent clot, lane 2; fibrinogen control, lane 3.