Col6a1^−/− platelets display an increased tendency toward activation and aggregation. (A) Platelet activation response in platelets from WT and Col6a1^−/− mice, measured 10 minutes after stimulation with 0.1 U/mL thrombin, 25 μM ADP, or 20 ng/mL CVX. Platelet activation was detected by the binding of the JON/A antibody against activated integrin αIIbβ3 (Ai) and the binding of the anti-CD62P antibody (Aii). Data are mean ± SD (n = 5). Student t test. (Bi) Representative aggregation response of washed platelets (1.7 × 10⁵/μL) prepared from WT and Col6a1^−/− mice. Platelets were stimulated with different agonists (collagen I 5 μg/mL, thrombin 0.5 U/mL, and ADP plus adrenaline 20 μM each, in the presence of 1 mM CaCl₂. Platelet aggregation was measured as a change in light transmission using a lumi-aggregometer. (Bii) Quantification of the percentage of maximal platelet aggregation. Data are mean ± SD (n = 3). Student t test. *P < .05, **P < .01. MFI, mean fluorescence intensity.