Lyn, but not Src, is required for aggregation, TxB2 production, and ATP secretion. (A) Aggregation and agglutination traces of washed wild-type (WT), Lyn^–/–, and Src^–/– mouse platelets treated with 0.5 μg/mL botrocetin (bt) and 10 μg/mL von Willebrand factor (VWF). WT platelets aggregated in the absence of EDTA and agglutinated in the presence of EDTA. EDTA chelates Ca²⁺, thereby preventing fibrinogen binding and platelet aggregation without affecting agglutination.⁹  Lyn-deficient platelets agglutinated, but failed to aggregate. Src^–/– platelets underwent delayed aggregation. (B) The level of TxA2 produced by bt/VWF-stimulated WT platelets in the presence of EDTA is characteristic of agglutination elicited TxA2 production. Lyn^–/– platelets did not produce TxA2 or secrete ATP, but Src^–/– platelets displayed about a 50% decrease of those functions. The numbers above the bars denote TxA2 produced (ng/mL) or ATP secreted (nM) in response to the indicated treatments. The error bars represent standard deviation, n = 3. In some cases, the values of the SD were so small that the bars cannot be seen.