Interaction of serum proteins with lung endothelial glycocalyx: its effect on endothelial permeability

To examine directly the interaction of circulating proteins (CP) with the glycocalyx of pulmonary endothelium and its effect on endothelial permeability, two types of experiments were carried out. In the first, rats were exchange transfused with graded amounts of FC-43 fluorocarbon emulsion (FCE) resulting in CP concentrations of 25, 10, and 4 mg/ml, respectively. In the second, rats were exchange transfused with FCE to remove 99.9% of CP. The rats were then exchange transfused with 1 ml FCE containing 60 mg/ml of rat serum protein and killed 3.5, 7.5, and 15 min after the administration of protein. In all animals the distribution of albumin and immunoglobulin G (IgG) was visualized by immunocytochemistry, and endothelial permeability to native ferritin was measured by morphometry. In the depletion experiments increased endothelial permeability to ferritin coincided with loss of adsorbed albumin and IgG from the glycocalyx. Conversely, the presence of administered serum proteins in the glycocalyx and in a few luminal vesicles was associated with an endothelial permeability to ferritin indistinguishable from that of controls. These observations suggest that the adsorption of CP to the endothelial glycocalyx renders the underlying endothelium less permeable to ferritin.