Binding and transcytosis of glycoalbumin by the microvascular endothelium of the murine myocardium: evidence that glycoalbumin behaves as a bifunctional ligand.
The binding and transport of glycoalbumin (gA) by the endothelium of murine myocardial microvessels were studied by perfusing in situ 125I-gA or gA-gold complexes (gA-Au) and examining the specimens by radioassays and EM, respectively. After a 3-min perfusion, the uptake of radioiodinated gA is 2.2-fold higher than that of native albumin; it is partially (approximately 55%) competed by either albumin or D-glucose, and almost completely abolished by the concomitant administration of both competitors or by gA. D-mannose and D-galactose are not effective competitors. Unlike albumin-gold complexes that bind restrictively to plasmalemmal vesicles, gA-Au labels the plasma-lemma proper, plasmalemmal vesicles open on the lumen, and most coated pits. Competing albumin prevents gA-Au binding to the membrane of plasmalemmal vesicles, while glucose significantly reduces the ligand binding to plasmalemma proper. Competition with albumin and glucose gives additive effects. Transcytosis of gA-Au, already detected at 3 min, becomes substantial by 30 min. No tracer exit via intercellular junctions was detected. gA-Au progressively accumulates in multivesicular bodies. The results of the binding and competition experiments indicate that the gA behaves as a bifunctional ligand which is recognized by two distinct binding sites: one, located on the plasma membrane, binds as a lectin the glucose residues of gA; whereas the other, confined to plasmalemmal vesicles, recognizes presumably specific domains of the albumin molecule.
Predescu
D
D
Institute of Cellular Biology and Pathology, Bucharest, Romania.
Simionescu
M
M
Simionescu
N
N
Palade
G E
GE
D000818:Animals; D001667:Binding, Competitive; D001692:Biological Transport; D002196:Capillaries / Q000378:metabolism / Q000648:ultrastructure; D004705:Endocytosis; D004730:Endothelium, Vascular / Q000378:metabolism* / Q000648:ultrastructure; D017127:Glycation End Products, Advanced; D006046:Gold; D007365:Intercellular Junctions; D051379:Mice; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism*; D000093423:Glycated Serum Albumin
D017127:Glycation End Products, Advanced; D012709:Serum Albumin; D006046:Gold; D000093423:Glycated Serum Albumin