Relationship between Platelet Aggregation and the Condition of GPIIb-IIIa Complex in Unstimulated Platelets

Abstract

We used a monoclonal antibody against GP IIb-IIIa complex (NNKY1-32) to study the relationship between platelet aggregation and the condition of GP II b- IIIa complex in unstimulated platelets. The quantities of GP II b- IIIa complex in Glanzmann's thrombasthenia (Type I, Type II), Heterozygote, EDTA-treated and cation-treated platelets were classified into three groups according to the binding of anti-GP IIb-IIIa complex antibody. Despite the similarity in binding of monoclonal anti-GP IIb-IIIa complex antibody within each groups, however, differences were found in platelet aggregability between samples. Ca²⁺ and Mg²⁺ promoted the reassociation of dissociated GP IIb and GP IIIa in intact cells, and restored aggregabilities of platelets. In particular, mixed materials (Ca²⁺ Mg²⁺ + auto-plasma) significantly restored ADP-induced aggregabilities of platelets. These results suggest the following. The conformational change of GP IIb / IIIa after platelet activation also depends on the conditions of complex formation by GP IIb and GP IIIa and the microenvironment around GP IIb / IIIa in resting platelets. Compl ex formation alone is insufficient for ADP-induced aggregation, and the presence of Ca²⁺, Mg²⁺and some factors in plsma appears to be necessary condition.