This study evaluated for the first time the binding of pDNA/polymer complexes (polyplexes) on a human lung microvascular endothelial cell (HLMEC) monolayer under flow conditions. A slide of a HLMEC monolayer was mounted on a parallel flow chamber connected to an open flow system from a reservoir containing fluorescent polyplexes to a syringe. A precise pump allowed their passage through the chamber under a range of shear stresses. The binding of polyethyleneimine (PEI)- and histidylated polylysine (His)-polyplexes was carried out over 30 min by time-lapse video microscopy. At 10 microg pDNA/ml in 10% serum, we found that 360+/-80 PEI- and 250+/-50 His-polyplexes were bound per 1000 cells at a shear stress of 0.3-1 dyn/cm(2). This number dropped to approximately 100 at 2 dyn/cm(2). These polyplexes exhibited differences in their interactions with the cell membrane. Concerning PEI-polyplexes, there was a shear threshold effect allowing a maximum binding at 0.06 dyn/cm(2) and a higher binding reduction (77%) at 5 microg/ml pDNA in 100% serum. The polyplex binding was augmented by 300% with PEI bearing tetraglucose moiety. This set-up is potentially helpful to screen a wide array of endothelial cells ligands prior in vivo experiments.