Albumin uptake and transcytosis in endothelial cells in vivo induced by albumin-binding protein

Am J Physiol Lung Cell Mol Physiol. 2001 Dec;281(6):L1512-22. doi: 10.1152/ajplung.2001.281.6.L1512.


The 60-kDa endothelial cell surface albumin-binding glycoprotein (gp60) is postulated to be a docking site for albumin that mediates the uptake of albumin and its transport in cultured microvessel endothelial cells. In the present study, we used an isolated Krebs-perfused rat lung preparation to address the in vivo role of gp60 in mediating albumin uptake and transport. Addition of primary anti-gp60 antibody to the perfusate followed by the secondary antibody to cross-link gp60 increased the vessel wall (125)I-albumin permeability-surface area (PS) product 2.5-fold without affecting the capillary filtration coefficient (K(f,c;) a measure of liquid permeability). In contrast, EDTA (5 mM), which induces interendothelial gap formation, produced parallel increases in both K(f,c) and (125)I-albumin PS product. Increasing perfusate albumin concentration to >1 g/100 ml (EC(50) 1.2 g/100 ml) was sufficient to block (125)I-albumin PS product, indicating that the perfusate albumin competed with tracer albumin for transendothelial albumin transport. Cross-linking of gp60 in lungs perfused with saturating concentration of albumin resulted in a greater increase in (125)I-albumin PS product, indicating that gp60 function was capable of being modulated. These results show that activation of gp60 in pulmonary microvessels induces albumin uptake and its transport through a non-hydraulic pathway that fits with a model of albumin permeability via the transcellular pathway.

MeSH terms

  • Albumins / pharmacokinetics*
  • Animals
  • Anti-Bacterial Agents / pharmacology
  • Antibodies / pharmacology
  • Capillary Permeability / drug effects
  • Capillary Permeability / physiology
  • Cells, Cultured
  • Cross-Linking Reagents
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / metabolism*
  • Filipin / pharmacology
  • Glycoproteins / immunology
  • Glycoproteins / metabolism*
  • Iodine Radioisotopes
  • Lung / blood supply*
  • Rats


  • Albumins
  • Anti-Bacterial Agents
  • Antibodies
  • Cross-Linking Reagents
  • Glycoproteins
  • Iodine Radioisotopes
  • Filipin