A transmural pressure gradient induces mechanical and biological adaptive responses in endothelial cells

A sudden increase in the transmural pressure gradient across endothelial monolayers reduces hydraulic conductivity (L_p), a phenomenon known as the sealing effect. To further characterize this endothelial adaptive response, we measured bovine aortic endothelial cell (BAEC) permeability to albumin and 70-kDa dextran, L_p, and the solvent-drag reflection coefficients (σ) during the sealing process. The diffusional permeability coefficients for albumin (1.33 ± 0.18 × 10^-6 cm/s) and dextran (0.60 ± 0.16 × 10^-6 cm/s) were measured before pressure application. The effective permeabilities (measured when solvent drag contributes to solute transport) of albumin and dextran (P_ealb and P_edex) were measured after the application of a 10 cmH₂O pressure gradient; during the first 2 h of pressure application, P _ealb, P_edex, and L_p were significantly reduced by 2.0 ± 03-, 2.1 ± 0.3-, and 3.7 ± 0.3-fold, respectively. Immunostaining of the tight junction (TJ) protein zonula occludens-1 (ZO-1) was significantly increased at cell-cell contacts after the application of transmural pressure. Cytochalasin D treatment significantly elevated transport but did not inhibit the adaptive response, whereas colchicine treatment had no effect on diffusive permeability but inhibited the adaptive response. Neither cytoskeletal inhibitor altered σ despite significantly elevating both L_p and effective permeability. Our data suggest that BAECs actively adapt to elevated transmural pressure by mobilizing ZO-1 to intercellular junctions via microtubules. A mechanical (passive) component of the sealing effect appears to reduce the size of a small pore system that allows the transport of water but not dextran or albumin. Furthermore, the structures of the TJ determine transport rates but do not define the selectivity of the monolayer to solutes (σ).