Platelet function is altered in the absence of CypD. (A) Procoagulant activity is shown. Platelets were left unstimulated or stimulated with thrombin (0.5 U/mL), convulxin (250 ng/mL), thrombin plus convulxin, or thrombin plus the indicated concentrations of H₂O₂. Thrombin generation was measured in a prothrombinase assay and is presented relative to unstimulated CypD^+/+ platelets (n = 5). #P < .05 compared with unstimulated CypD^+/+ platelets; *P < .05 for comparison between CypD^+/+ and CypD^−/− platelets. (B,C) Clot retraction in diluted platelet-rich plasma is demonstrated. Clot formation was initiated by the addition of calcium together with thrombin (0.5 U/mL), convulxin (250 ng/mL), or thrombin plus convulxin. (B) Images of clots removed from serum 2 hours after initiation of clot formation. (C) The volume of the clot was determined 2 hours after initiation of clot formation by the indicated agonist(s) (n = 6). #P < .05 compared with thrombin-initiated CypD^+/+ plasma; *P < .05 for comparison between CypD^+/+ and CypD^−/− plasma. Error bars represent SE.