Evidence that fibronectin is the collagen receptor on platelet membranes

Evidence is presented that fibronectin is present on the platelet cell membrane and that it is a receptor for collagen in the platelet-collagen interaction. First, sodium dodecyl sulfate/acrylamide gel electrophoresis was performed on the proteins remaining attached to the surface of collagen after the removal of the remainder of the platelet by sonication. The material was relatively enriched in a glycoprotein that comigrated with cold-insoluble globulin (CIG), a form of fibronectin, and in other proteins which comigrated with myosin, actin, and tropomyosin. The presumptive presence of contractile proteins is consistent with the presence of microfibrillar proteins. Second, the collagen-attached material was shown to contain a protein that reacted with anti-CIG serum by immunoelectrophoresis. Third, when CIG was preincubated with fibrous collagen, the platelet-collagen interaction was inhibited. Fourth, rabbit anti-human CIG stimulated human platelets to secrete the contents of their dense granules. The stimulation was not due to antibody complexes present in the solution. Fifth, a protein was extracted from well-washed platelets and purified on affinity columns of anti-CIG antibodies. The isolated protein was found to bind to fibrous collagen.