To examine the effect of shear stress on hydraulic conductivity (Lp) of bovine aortic endothelial cell monolayers grown on polycarbonate filters, we developed a rotating disk system, which imposed a defined shear stress while Lp was measured. A 10-cmH2O pressure differential was applied to monolayers, and baseline Lp was established between 1.65 +/- 0.85 and 4.94 +/- 1.05 x 10(-7) cm.s-1.cmH2O-1. One-hour exposure to 10 dyn/cm2 shear stress caused a significant (P < 0.05) increase in Lp by 2.16-fold (+/- 0.42), and Lp remained elevated when shear stress was removed. Three-hour exposure to shear stresses between 0.1 and 20.0 dyn/cm2 revealed a threshold for shear-induced increase in Lp of 0.5 dyn/cm2. At 20 dyn/cm2, Lp initially decreased by 30% (+/- 13.4%, P < 0.05) and then increased to a level 3.76-fold (+/- 0.83, P < 0.05) greater than baseline Lp at 3 h. The shear-induced increase in Lp was reversed with dibutyryl adenosine 3',5'-cyclic monophosphate (DBcAMP, 1 mM) and could be significantly (P < 0.05) inhibited when monolayers were preincubated with 0.3 mM DBcAMP, a concentration that did not significantly affect baseline Lp. Furthermore, preincubation with a general phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine (1 mM), completely blocked the shear-induced increase in Lp. On the basis of these results, we conclude that shear stress alters endothelial Lp through a cellular mechanism involving signal transduction, not by a purely physical mechanism.

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SUMMARY:Methods were developed to measure albumin permeability and electrical resistance of bovine aortic endothelial cell (BAEC) monolayers cultured on porous polycarbonate filters. Permeability to 1% bovine serum albumin (Pe) was quantified by measuring the flux of fluorescent-labeled albumin with an apparatus in which there were no transmural oncotic or hydrostatic pressure gradients. The effect of passage of BAEC monolayers in culture on permeability was studied using 60 BAEC monolayers of Passage 6 to 10. There was no significant difference in Pe between passages, and the mean Pe of all monolayers was 4.5 + 0.5 (SEM) X 10 -6 cm/s. Using these same BAEC monolayers, a fluorescent technique was developed to examine en face permeability patterns. Most BAEC monolayers demonstrated diffuse permeability across the monolayer, whereas others had focal regions of enhanced permeability despite similar Pe values. In those monolayers with punctate permeability, there were 5.4 + 0.6 (SEM) focal regions of enhanced permeability per 1000 cells. To study the effect of culture time on monolayer integrity, electrical conductivities of nine BAEC monolayers were measured daily using a Millipore electrical resistance system. Electrical resistance increased from 4.5 ohm-cm 2 at Day 2 to a peak level of 11.4 ohm" cm 2 at Day 7 and then decreased daily to 4.0 ohm. cm 2 by Day 12. The in vitro BAEC monolayer has many of the transport characteristics of intact vessels, making these techniques useful in physiologic studies of the endothelial transport barrier. These methods provide relatively simple means of assessing the integrity of endothelial cell monolayers grown on porous substrates.

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