ABSTRACT
This chapter focuses on the role of fibronectin (Fn) in platelet function and the possible value of the platelet system as a model for understanding the binding and processing of Fn by other cells. It highlights the similarities and differences between Fn and the other three members of the "Big Four". To participate in adhesive reactions, a protein must bind to the cell surface. In addition, platelet aggregation in response to ADP or thrombin proceeds normally in Fn-depleted plasma. The chapter also focuses on the evidence for platelet pools of each of these proteins and their localization in resting platelets. In the case of Fn, the initial surface expression is probably too rapid to be accounted for by rebinding, suggesting that at early timepoints the second mechanism predominates. Incubation of I-plasma Fn with thrombin-stimulated suspensions of washed human platelets results in time-dependent binding of Fn to the cells. Occupancy of adhesion receptors leads to a host of cellular responses.
