PDE2A3 transfection destabilized endothelial integrity of HUVEC monolayer. HUVECs were grown on polycarbonate filter membranes to confluency before applying hydrostatic pressure (10 cm H₂O) and measuring endothelial permeability. Hydraulic conductivity of resting (“sealed”) HUVECs was less than 1 × 10^-5 cm × s^-1 × cm H₂O^-1 for both pPDE2A3-transfected and nontransfected HUVECs. Cells were preincubated with PDP (1 μM) for 15 minutes before thrombin stimulation (1 U/mL). pPDE2A3-transfected monolayers responded with a significantly higher increase of hydraulic conductivity compared with control cells. This enhanced sensitivity of pPDE2A3-transfected monolayers was suppressed in the presence of PDP, confirming specificity of PDE2 transfection. Mock-transfected cells (empty pcDNA3.1 vector) did not show differences to untransfected cells. ○ indicates pPDE2A3 + thrombin; ▿, thrombin only; ⬡, pPDE2A3 + PDP + thrombin; ▾, PDP + thrombin; □, pPDE2A3 only; ^*, PDP only; and ▵, control. Data presented are mean ± SEM of 3 independent experiments. ^*P < .05 versus thrombin-stimulated cells.