title: Absorption of intact albumin across rat alveolar epithelial cell monolayers.
abstract: Transport characteristics of intact albumin were investigated using primary cultured rat alveolar epithelial cell monolayers. The apical-to-basolateral (ab) flux of intact fluorescein isothiocyanate (FITC)-labeled albumin (F-Alb) is greater than basolateral-to-apical (ba) flux at the same upstream [F-Alb]. Net absorption of intact F-Alb occurs with half-maximal concentration of approximately 1.6 microM and maximal transport rate of approximately 0.15 fmol.cm(-2).s(-1). At 15 and 4 degrees C, both ab and ba F-Alb fluxes are not different from zero, collapsing net absorption. The presence of excess unlabeled albumin (but not other macromolecule species) in either the apical or basolateral fluid significantly reduces both ab and ba unidirectional F-Alb fluxes. Photoaffinity labeling of apical cell membranes revealed an approximately 60-kDa protein that exhibits specificity for albumin. These data indicate that net absorption of intact albumin takes place via saturable receptor-mediated transcellular endocytotic processes recognizing albumin, but not other macromolecules, that may play an important role in alveolar homeostasis in the mammalian lung.
authors.affiliation: Department of Medicine, School of Medicine, University of Southern California, Los Angeles, California 90033, USA. kjkim@usc.edu
authors.forename: Kwang-Jin
authors.initials: KJ
authors.lastname: Kim
authors.forename: Yasuhisa
authors.initials: Y
authors.lastname: Matsukawa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yamahara
authors.forename: Vijay K
authors.initials: VK
authors.lastname: Kalra
authors.forename: Vincent H L
authors.initials: VH
authors.lastname: Lee
authors.forename: Edward D
authors.initials: ED
authors.lastname: Crandall
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000502:physiology; D002478:Cells, Cultured; D017097:Electric Impedance; D004847:Epithelial Cells / Q000166:cytology / Q000378:metabolism*; D016650:Fluorescein-5-isothiocyanate / Q000031:analogs & derivatives* / Q000378:metabolism / Q000493:pharmacokinetics; D005456:Fluorescent Dyes; D008297:Male; D011485:Protein Binding / Q000502:physiology; D021381:Protein Transport / Q000502:physiology; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D012709:Serum Albumin / Q000378:metabolism*; D012710:Serum Albumin, Bovine / Q000378:metabolism / Q000493:pharmacokinetics; D012964:Sodium / Q000378:metabolism; D013047:Specific Pathogen-Free Organisms; D013696:Temperature
chemical_list: D005456:Fluorescent Dyes; D012709:Serum Albumin; C039217:fluorescein isothiocyanate bovine serum albumin; D012710:Serum Albumin, Bovine; D012964:Sodium; D016650:Fluorescein-5-isothiocyanate