Role of exogenous fibrinogen in the processes of degranulation of thrombocytes stimulated with thrombin. Ultrastructural study using fibrinogen labeled with colloidal gold

: Using colloidal gold-conjugated fibrinogen (F-Au) it is shown that exogenous fibrinogen can participate in the platelet release reaction. In the absence of F-Au, internal secretory vacuoles readily formed in human platelets stimulated with thrombin, but extrusion of their content was delayed. Upon incubation with F-Au, endocytic channels induced by F-Au-receptor interactions, fused with internal vacuoles, thus establishing spatial communications of the latter with the outer medium.