Catalase inhibits collagen-induced ATP secretion both in untreated and aspirin-treated platelets. (A) TC of collagen; TC collagen plus catalase (250, 500, and 1,000 U/mL). (B) ATP release in platelets stimulated with TC of collagen in ASA (100 μmol/L)-treated platelets stimulated with TC and fourfold to eightfold TC of collagen added with or without catalase (250 U/mL). Data are expressed as the mean ± SEM of five separate experiments (*P < .01; **P < .001).