LAT^−/− mice are protected from JAQ1-induced bleeding. (A) LAT^−/− mice received 100 μg JAQ1 or JAQ3 intraperitoneally, and platelets were isolated on day 5 and tested in Western blot analysis for the presence of GPIIIa (EDL1) or GPVI (JAQ1, JAQ2, JAQ3). (B) Wild-type or LAT^−/− mice received vehicle or 20 μg JAQ1 intravenously and platelets were isolated on day 5 followed by aggregometric analysis of convulxin (cvx)–induced aggregation. The arrows indicated the addition of the agonist (5 μg/mL). The results are representative of 6 individual experiments. (C) JAQ1 does not alter thrombin responses in LAT^−/− mice. Washed platelets were prepared at the indicated time points after JAQ1 treatment and stimulated with 0.1 (▾), 0.01 (○), or 0.001 (•) U/mL thrombin. Activation of integrin αIIbβ3 and surface expression of P-selectin were determined by flow cytometry and are given as percentage ± SD of the values obtained with untreated controls (n = 6 per group). Platelets were gated by FSC/SSC characteristics and FL-4 positivity (anti–GPIbα-Cy5). (D) Tail bleeding times in wild-type and LAT^−/− mice 24 hours after treatment with vehicle or 20 μg JAQ1.