Schematic illustration of phosphodiesterases (PDEs) in endothelial cells. The cartoon highlights the roles of cyclic adenosine monophosphate (cAMP), cyclic guanosine monophosphate (cGMP), and various PDEs (PDE2, 3, and 4) in regulating endothelial cell permeability. ANP, atrial natriuretic peptide; Epac, exchange protein activated by cAMP; NO, nitric oxide; PKA, protein kinase A, TGF-β, transforming growth factor β; TNF-α, tumor necrosis factor α; VEGF, vascular endothelial growth factor.