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The contribution of integrin receptors to the regulation of endothelial permeability was studied using cultured bovine pulmonary microvascular endothelial cell (BPMVEC) monolayers by the measurement of hydraulic conductivity (Lp). Treatment of monolayers with a peptide containing the sequence Gly-Arg-Gly-Asp-Ser-Pro (GRGDSP) (0.85 mM) to compete for the RGD sequence of extracellular matrix (ECM) proteins increased endothelial Lp threefold, whereas the control peptide Gly-Arg-Gly-Glu-Ser-Pro had no effect on Lp. This action of GRGDSP on Lp was not significantly altered by dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP; 0.5 mM). Endothelial Lp increased twofold when the monolayers were challenged with alpha-thrombin (5 x 10(-8) M for 10 min), and this response was completely reversed by DBcAMP. The strength of adhesion of endothelial cells was estimated by evaluating the ability of endothelial cells to remain attached to ECM after treating the monolayers with 0.05% trypsin plus 0.5 mM EDTA. Exposure of the monolayers to either GRGDSP or alpha-thrombin significantly reduced the strength of adhesion to the ECM. DBcAMP prevented the antiadhesive effect of alpha-thrombin but not that of GRGDSP. Treatment of the monolayers with either alpha-thrombin or GRGDSP caused formation of intercellular gaps, but only the thrombin-induced intercellular gaps were accompanied by reorganization of actin filaments. These results indicate that integrin binding to ECM proteins regulates an important determinant of endothelial permeability and that alpha-thrombin and GRGDSP increase endothelial cell monolayer permeability by different mechanisms.
Qiao et al. (Sat,) studied this question.