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

We used a monoclonal antibody against GP II bIIIa complex (NNKY1-32) to study the relationship between platelet aggregation and the condition of GP II bIII a complex in unstimulated platelets. The quantities of GP II bIII a 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 I I bIII a complex antibody. Despite the similarity in binding of monoclonal anti-GP II bIII a complex antibody within each groups, however, differences were found in platelet aggregability between samples. (a2+ and Mg2+ promoted the reassociation of dissociated GP II b and GP III a 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 II b/ III a after platelet activation also depends on the conditions of complex formation by GP II b and GP III a and the microenvironment around GP II b/ III a in resting platelets. Complex formation alone is insufficient for ADP-induced aggregation, and the presence of Ca2+, Mg2+ and some factors in plsma appears to be necessary condition.