Compound 1 does not prevent platelet adhesion to collagen, but does prevent recruitment of additional platelets to adherent platelets; compound 1 and the anti-αIIbβ3 mAb 10E5 only partially inhibit platelet deposition on immobilized collagen, and their effects are not additive. (A) Washed platelets were allowed to adhere to collagen on a glass slide for 1 hour, and were then labeled with Alexa-488–conjugated anti-β3 mAb 7H2. Confocal microscopy images were obtained with a 100× objective as described in “Platelet and cell adhesion.” (B) Washed platelets were left untreated or treated with DMSO (1%); compound 1 at 20, 50, or 100 μM, with or without mAb 10E5 (20 μg/mL); mAb 10E5; or mAb 6F1 (anti-α2β1, 20 μg/mL) for 15 minutes at 37°C before being added to microtiter wells coated with collagen. After 1 hour, nonadherent platelets were removed by washing and the number of adherent platelets was determined by pNPP assay as described in “Platelet and cell adhesion.” Adhesion is expressed as the percentage of adhesion of control, DMSO (1%)–treated platelets. The mean and SD of 4 separate experiments is depicted for each condition.