FIGURE 1.

PDE3A activity increases upon stimulation of platelets with thrombin. Washed platelets were stimulated with 0.1 unit/ml thrombin for 5 min, and 3′-cAMP phosphodiesterase activity was measured in whole cell lysates. Samples were depleted of PDE3A by immunoprecipitation with a PDE3A specific antibody and phosphodiesterase activity measured in depleted lysates and immunoprecipitates. ^*, p < 0.05 (A). PDE3A immunoprecipitates were assayed for 3′-cAMP phosphodiesterase activity in the presence of the indicated compounds (B). K_m and V_max were determined from PDE3A immunoprecipitates from basal and thrombin-stimulated platelets by non-linear regression of substrate saturation curves. A Lineweaver-Burk linear transformation is in-set into the plot (C).