Aberrant platelet activation in G6b-B diY/F mice. (A) Blood loss/body weight ratio following excision of 5 mm of tail tip in isoflurane-anesthetized mice of the indicated genotypes. Data were analyzed using a bimodal function, comprising a gamma and normal distribution for low- and high-bleeding tendency, respectively. Likelihood ratio tests were performed to determine whether the probability of bleeding (Pbleed) differed between genotypes. (B-D) Flow cytometric measurement of P-selectin exposure and fibrinogen binding of WT and G6b-B diY/F platelets in whole blood using ITAM-activating (Bi-ii) and G protein–coupled receptor–activating (Ci-ii) agonists (mean ± SEM, n = 5 or 6 per stimulation). Thrombin stimulation was in the presence of 10 μM glycine-proline-arginine-proline to prevent blood clotting. (Di-ii) Rescue of activating PAR4 peptide (PAR4p)-stimulated fibrinogen binding in the presence of 10 μM ADP (mean ± SEM, n = 5 or 6). Platelets were gated using forward and side scatter, and 10 000 events were collected. *P < .05; **P < .01; ***P < .001.