ADHESION OF ADP-ACTIVATED PLATELETS TO INTACT ENDOTHELIUM UNDER STAGNATION POINT FLOW IN-VITRO IS MEDIATED BY THE INTEGRIN ALPHA-IIB-BETA-3

As we demonstrated earlier, platelets adhere to intact endothelium pro vided they are activated and convectively transported against the endo thelial surface. To identify the platelet receptors involved rye super fused cultured endothelium with activated platelet rich plasma (PRP) b y means of the Stagnation Point Flow Adhesio- Aggregometer while block ing various platelet receptors. inhibition was performed with the tetr apeptide RGDS, the non-peptide Ro-43-8857, or a monoclonal antibody di rected against integrin alpha IIb beta 3. Platelet deposition was vide o-recorded and quantified by image analysis. Infusion of RGDS or Ro-43 -8857 into ADP-stimulated PRP completely prevented adhesion as well as subsequent aggregation. Interrupting the inhibitor infusion while ADP stimulation persisted, prompted adhesion and aggregation, demonstrati ng the reversibility of the inhibition. Platelet adhesion was irrevers ibly blocked by preincubation of the PRP with the moab against alpha I Ib beta 3. Its specific binding was confirmed by immunoelectron micros copy. Our results suggest that platelet adhesion to intact endothelium is mediated via platelet integrin alpha IIb beta 3.