Heterogeneity of intimal and microvessel endothelial cell barriers in vitro

We have compared the barriers provided by bovine aortic endothelial cells (AEC), cerebral microvessel endothelial cells (CMEC), and pulmonary microvessel endothelial cells (PMEC) cultured on microcarriers to the passage of trypan blue-bovine serum albumin (TB-BSA). AEC and PMEC barriers were quantitatively comparable, and significantly more permeable to TB-BSA than the CMEC barrier. Serotonin, norepinephrine, and histamine, shown to modulate the AEC barrier, had no effect on the CMEC barrier to TB-BSA. These results suggest that cultured endothelial cells (EC) retain region-specific phenotypic modifications of barrier function observed in vivo. Glutaraldehyde-fixed EC and EC kept at 4 degrees C to minimize transcytosis displayed TB-BSA passage that was reduced by less than 30%, which indicated that the bulk of tracer movement occurred via diffusion between EC. Treatment with cytochalasin B (5 micrograms/ml) resulted in significant AEC and CMEC barrier loss. These results suggest that microfilament bundles are involved in maintaining EC close junctional apposition. We have reported previously that exogenous serotonin and norepinephrine stimulate the EC barrier function in vivo and in vitro, and modulate EC motility, shape, and stress fiber assembly in vitro. In light of these data and the present results, we hypothesize that EC motility and shape change determine in part intercellular macromolecular diffusion by way of a dynamic system of pores of varying radii.