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 6 0 min irreversibly dissociated glycoprotein (GP) IIb/IIIa complex (alp ha(IIb)beta(3) integrin) on the surface membrane, since transmission i mmunoelectron microscopy studies demonstrated that these EDTA-pretreat ed platelets in the presence of added Ca2+ ion could not bind P2, an a nti-GPIIb/IIIa complex-specific monoclonal antibody, to their surface membrane. The treatment, however, had no effect on the GPIIb/IIIa comp lex on the alpha-granule membrane. At 30 sec after the EDTA-pretreated platelets were activated with 0.1 U/ml of thrombin, alpha-granules fu sed with each other or with the surface-connected canalicular system ( SCCS) to form swollen SCCS, the membrane of which was found to have th e intact GPIIb/IIIa complex detectable by P2. In addition, at this tim e the intact GPIIb/IIIa complex reappeared on the surface membrane. At 5 min. the intact GPIIb/IIIa complex increased on the surface membran e with a reciprocal decrease or disappearance an the membrane of the s wollen 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 red istributed to the surface membrane via the membrane of SCCS during the release reaction.