P2Y12 in Atherothrombosis Figure 5. Inhibition of P2Y12 receptors affects collagen-dependent thrombus formation at high but not low shear rate. Citrate- anticoagulated human blood, recalcified with CaCl2/MgCl2 in the presence of 2 pM tissue factor, was perfused over Horm type I collagen at a shear rate of 300 or 1000 s21. Blood samples were preincubated with vehicle, ticagrelor (20 mM) or cangrelor (10 mM), as indicated. (A) Representative phase-contrast images after 4 min of perfusion (bar = 20 mm). (B) Average size of thrombi formed in treated blood samples at different shear rates. (C) Frequency distribution of feature size on coverslips; estimated numbers of platelets per feature (aggregate) were: 9–24 (white), 24–75 (light gray), 75– 400 (dark gray) and .400 (black). (D) Number of disaggregation events from individual aggregates in the 4th minute of blood perfusion at 300 or1000 s21. Data are means 6 SE (n = 3–9), *p,0.05 compared to vehicle. doi:10.1371/journal.pone.0010130.g005 the reversible P2Y12 inhibitor ticagrelor [41,42] have shown promising results for the treatment of acute coronary syndrome. Our findings suggest that the success of such anti-P2Y12 interventions relies on the selective abrogation of a platelet response–autocrine activation of P2Y12–that is at least in part dependent on the local, high shear conditions. In summary, we have shown that ADP, via P2Y12, stabilizes thrombi on ruptured plaques both in vivo and on human PLoS ONE | www.plosone.org 9 April 2010 | Volume 5 | Issue 4 | e10130