Time-dependent VASP phosphorylation and inhibition of thrombin-induced platelet activation by the cGK activator 8-pCPT-cGMP in human platelets. Washed human platelets (3 × 10⁸/mL) were preincubated with 8-pCPT-cGMP (200 μM) for the times indicated (0.5-10 minutes) followed by a 1-minute incubation with thrombin (0.5 U/mL). Platelet activation was monitored by the analysis of P-selectin expression (FACS) and ERK phosphorylation (Western blots), cGK activation by the analysis of VASP phosphorylation (P-VASP Western blots). Note the significant inhibition of platelet activation by 8-pCPT-cGMP at early time points (0.5-2 minutes) without corresponding VASP phosphorylation. Results are representative of 3 different experiments as means ± SEM.