Selectivity of the endothelial monolayer: effects of increased permeability.

We investigated the mechanism of thrombin-induced increases in endothelial monolayer permeability by examining the effect of thrombin on the molecular sieving characteristics of the endothelial monolayer and comparing the responses of arterial- and venous-derived endothelial cell lines. Bovine pulmonary artery (BPA) and pulmonary vein (BPV) endothelial cells were similarly harvested and cultured. The endothelial cells were grown to confluence on gelatinized polycarbonate filters and the permeabilities to sucrose, albumin, and IgG were measured and corrected for effects of unstirred layers. The control permeabilities of BPA and BPV were similar with both monolayers, demonstrating selectivity to different sized tracer molecules. alpha-Thrombin (10(-6) M) increased the permeability of both BPA and BPV to albumin and sucrose. The permeability of BPA was increased to a greater extent than BPV, perhaps due to phenotypic differences. In both cell lines, the permeability increase was most pronounced for albumin, which by pore theory is best described by an increase in the radius of the small pore pathway for diffusion.