Summary
As we demonstrated earlier, platelets adhere to intact endothelium provided they are
activated and convectively transported against the endothelial surface. To identify
the platelet receptors involved we superfused cultured endothelium with activated
platelet rich plasma (PRP) by means of the Stagnation Point Flow Adhesio- Aggregometer
while blocking various platelet receptors. Inhibition was performed with the tetrapeptide
RGDS, the non-peptide Ro-43-8857, or a monoclonal antibody directed against integrin
αIIbβ3. Platelet deposition was video-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, demonstrating the reversibility of the
inhibition. Platelet adhesion was irreversibly blocked by preincubation of the PRP
with the moab against αIIbβ3. Its specific binding was confirmed by immuno-electron
microscopy. Our results suggest that platelet adhesion to intact endothelium is mediated
via platelet integrin αIIbβ3.