Detection of caspase-3 in resting and activated platelets. (A) Caspase-3–like peptidase activity (cleavage of DEVD-pNA) of Triton X-100 lysates of resting platelets (0 time point) and platelets activated by A23187. Data shown are the mean ± SEM (n = 5). Peptidase activity was significantly increased relative to resting platelets after 5, 10, and 20 minutes with A23187 (*P < .01). In the sample 20 min + DEVD, the inhibitor DEVD-fmk was present during platelet activation and peptidase assay. (B) Caspase-3 antigen detected by immunoblot. Resting platelets and platelets activated with A23187 for 10, or 20 minutes were stained with caspase-3–specific MoAb C31720. Molecular weight marker positions are shown on the left and an arrow indicates 32-kD procaspase-3. The lanes MNC (mononuclear cell lysates treated without and with granzyme B) control for the ability to detect active caspase-3, the large subunit of which (p17) is indicated by the arrow on the right. (C). Procaspase-3 antigen quantified by immunoblots. Data shown are the mean ± SEM (n = 4). Platelet content of procaspase-3 antigen was significantly decreased relative to resting platelets after 10 (*P < .02) and 20 minutes (*P <.003) with A23187.