title: Transport properties of alveolar epithelium measured by molecular hetastarch absorption in isolated rat lungs.
abstract: To evaluate the transport properties of the alveolar epithelium, we instilled hetastarch (Het; 6%, 10 ml, 1 - 1 x 10(4) kDa) into the trachea of isolated rat lungs and then measured the molecular distribution of Het that entered the lung perfusate from the air space over 6 h. Het transport was driven by either diffusion or an oncotic gradient. Perfusate Het had a unique, bimodal molecular weight distribution, consisting of a narrow low-molecular-weight peak at 10-15 kDa (range, 5-46 kDa) and a broad high-molecular-weight band (range 46-2,000 kDa; highest at 288 kDa). We modeled the low-molecular-weight transport as (passive) restricted diffusion or osmotic flow through a small-pore system and the high-molecular-weight transport as passive transport through a large-pore system. The equivalent small-pore radius was 5.0 nm, with a distribution of 150 pores per alveolus. The equivalent large-pore radius was 17.0 nm, with a distribution of one pore per seven alveoli. The small-pore fluid conductivity (2 x 10(-5) ml. h(-1). cm(-2). mmHg(-1)) was 10-fold larger than that of the large-pore conductivity.
authors.affiliation: Department of Surgery, The William S. Middleton Memorial Veterans Hospital, University of Wisconsin-Madison, Madison, WI 53792-7375, USA. rconhaim@facstaff.wisc.edu
authors.forename: R L
authors.initials: RL
authors.lastname: Conhaim
authors.forename: K E
authors.initials: KE
authors.lastname: Watson
authors.forename: S J
authors.initials: SJ
authors.lastname: Lai-Fook
authors.forename: B A
authors.initials: BA
authors.lastname: Harms
mesh_terms: D000042:Absorption; D000465:Algorithms; D000818:Animals; D001693:Biological Transport, Active / Q000502:physiology; D002462:Cell Membrane / Q000378:metabolism; D002850:Chromatography, Gel; D004848:Epithelium / Q000378:metabolism / Q000648:ultrastructure; D006895:Hydroxyethyl Starch Derivatives; D066298:In Vitro Techniques; D008168:Lung / Q000378:metabolism* / Q000648:ultrastructure; D008297:Male; D008854:Microscopy, Electron; D008970:Molecular Weight; D010952:Plasma Substitutes; D016062:Porosity; D011650:Pulmonary Alveoli / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats
chemical_list: D006895:Hydroxyethyl Starch Derivatives; D010952:Plasma Substitutes