PP1 reverses thrombin-induced activation of PDE3A. A series of paired samples of washed platelets (2 × 10⁸/mL) were incubated with thrombin at 37°C for 3 minutes in the presence of 20 μmol/L EHNA to limit the PDE2A effect. The reactions were stopped by addition of 0.5% Triton X-100. One of the paired samples was treated with PP1 and the other incubated with vehicle. Dephosphorylation by PP1 was carried out as described in “Materials and methods, Dephosphorylation of PDE3,” and PDE3A activities were immediately measured after the dephosphorylation procedure. Data are from 4 experiments using different donor platelets and are means plus or minus SEM.