Change of platelets surface conformation in ADP- and collagen-induced aggregation

Abstract

We used four monoclonal antibodies against platelet membrane and flow cytometry to study the conformational change on the platelet surface in ADP or collagen stimulation. If ADP or collagen was added to normal PRP or to washed platelets that had been incubated with various buffers, the binding of fibrinogen and monoclonal anti-GPIIb/IIIa complex antibodies changed. On the other hand, when ADP was added to PRP preincubated with monoclonal anti-GPIb antibody, the increase of light transmission continued and the fixed binding of fibrinogen was observed. The results obtained from this study following possibilities.
1. The binding sites fibrinogen are newly expressed on GPIIb/IIIa complex by the stimulation of agonist or the extracellular Ca²⁺ concentration, and the GPIIb/IIIa complex increases quantitatively in the case.
2. The binding GPIIb/IIIa complex is stable at Ca²⁺ concentration near the in vivo level and the structure hardly changes on stimulation by a weak agonist such as ADP.
3. The binding of vWF to GPIb after ADP stimulation inhibits the dissociation of the first aggregation or enhances the aggregation.