Catalase inhibits collagen-induced calcium mobilization both in untreated and ASA-treated platelets. (A) Calcium mobilization in collagen-stimulated platelets added with or without 250, 500, or 1,000 U/mL catalase. Data are expressed as the mean ± SEM of five separate experiments (*P < .05; **P < .01). (B) Calcium mobilization in ASA (100 μmol/L)-treated platelets with or without catalase (250 U/mL) stimulated with scalar concentrations of collagen. Data are expressed as the mean ± SEM of five separate experiments (*P < .05; **P < .01). (C) Cytosolic calcium concentration induced by collagen (40 μg/mL) was reduced by catalase (250 U/mL) in platelets pretreated with aspirin (100 μmol/L) and the ADP scavenger system CP/CPK. Data are expressed as the mean ± SEM of five separate experiments (*P < .01).