Endothelial monolayer permeability to macromolecules.

The barrier function of the endothelial monolayer has not been extensively investigated using the cultured endothelium. The in vitro approach may contribute to a more complete understanding of microvessel wall permeability. Our studies using an in vitro endothelial monolayer system have led us to the following conclusions: the endothelial monolayer is more permeable to small-molecular-weight substances than to large molecules; the permeability of albumin is different for endothelial cells derived from different vascular sites (higher for pulmonary venous than pulmonary arterial endothelium); basement membrane components may have a significant role in the permeability of albumin across the endothelium; control of endothelial monolayer permeability is determined not only by the characteristics of the macromolecule (i.e., size and charge) but also by the shape of the endothelial cells and the size of interendothelial space.