Integrin α2β1-induced activation of Rap1b does not require platelet-derived secondary agonists. Platelet adhesion to monomeric collagen was analyzed using washed platelets preincubated with the ADP scavengers CP/CPK or apyrase or with the ADP receptor antagonists A3P5PS or AR-C69931MX (A) or upon treatment with the cyclooxygenase inhibitors aspirin (asa) and indomethacin (indo) or with the thromboxane A2 receptor antagonist SQ29548 (B), as described in “Materials and methods.” The immunoblots show both active Rap1b (Rap1b-GTP) and total Rap1b (Rap1b TOT) isolated from the same number of adherent platelets. The effect of the different treatments on the extent of platelet adhesion is reported on the top of the panels (adhesion, %), considering as 100% the adhesion of nontreated platelets.
