Redistribution of alpha-granule membrane glycoprotein IIb/IIIa (integrin alpha IIb beta 3) to the surface membrane of human platelets during the release reaction.

Treatment of human washed platelets with 5 mM EDTA at 37 degrees for 60 min irreversibly dissociated glycoprotein (GP) IIb/IIIa complex (alpha IIb beta 3 integrin) on the surface membrane, since transmission immunoelectron microscopy studies demonstrated that these EDTA-pretreated platelets in the presence of added Ca2+ ion could not bind P2, an anti-GPIIb/IIIa complex-specific monoclonal antibody, to their surface membrane. The treatment, however, had no effect on the GPIIb/IIIa complex on the alpha-granule membrane. At 30 sec after the EDTA-pretreated platelets were activated with 0.1 U/ml of thrombin, alpha-granules fused with each other or with the surface-connected canalicular system (SCCS) to form swollen SCCS, the membrane of which was found to have the intact GPIIb/IIIa complex detectable by P2. In addition, at this time the intact GPIIb/IIIa complex reappeared on the surface membrane. At 5 min, the intact GPIIb/IIIa complex increased on the surface membrane with a reciprocal decrease or disappearance on the membrane of the swollen SCCS. The observation under scanning immunoelectron microscopy also confirmed the same translocation of the intact GPIIb/IIIa complex. These results indicate that alpha-granule membrane GPIIb/IIIa is redistributed to the surface membrane via the membrane of SCCS during the release reaction.