Binding and uptake of native and glycosylated albumin-gold complexes in perfused rat lungs

We have examined, by electron microscopy, the effect of glycosylation on binding, uptake, and transport of albumin-gold complexes in capillaries of isolated perfused rat lungs. Lungs were perfused for 2 min at 4 degrees with native and glycosylated albumin-coated gold particles. After the excess probe was washed out for 5 min the lungs were fixed immediately or perfused for 30 and 60 min at 37 degrees with a isoosmotic buffer before fixation. The localization and density of the probes over different microvascular endothelial compartments were determined by electron microscopy. We found that both native and glycosylated albumin were bound to the surface of the pulmonary microvascular endothelium, preferentially over the stomatal diaphragms of luminal smooth-walled vesicles. In both BSA and glycosylated BSA perfusions at 37 degrees, most of the probe was internalized and accumulated in lysosomes and only a few gold particles were observed in the extravascular compartment even after 60 min perfusion. However, binding, internalization, and transport of the protein-gold complexes was enhanced by nonenzymatic glycosylation of albumin.