cAMP concentrations in ADP-stimulated platelets. Washed wild-type (white bars) and caspase-12^–/– (dotted bars) platelets were incubated with PGE₁ followed by ADP stimulation at the indicated concentrations. The y-axis shows the cAMP concentration, with PGE₁-stimulated levels given a value of 100%. Data presented are the means ± SEM from 3 independent experiments. Platelet cAMP levels prior to PGE₁ stimulation (basal) are less than 10% of that seen following PGE₁ stimulation.