title: Luminal hyperosmolarity decreases Na transport and impairs barrier function of sheep rumen epithelium.
abstract: The effects of luminal hyperosmolarity on Na and Cl transport were studied in rumen epithelium of sheep. An increase of luminal osmotic pressure with mannitol (350 and 450 mosm/l) caused a significant increase of tissue conductance, G (T), which is linearly correlated with flux rates of (51)Cr-EDTA and indicates an increase of passive permeability. Studies with microelectrodes revealed, that an increase of the osmotic pressure caused a significant increase of the conductance of the shunt pathway from 1.23 +/- 0.10 (control) to 1.92 +/- 0.14 mS cm(-2) (450 mosm/l) without a change of fractional resistance. Hyperosmolarity significantly increased J (sm) and reduced J (net) Na. The effect of hyperosmolarity on J (ms) Na is explained by two independent and opposed effects: increase of passive permeability and inhibition of the Na(+)/H(+) exchanger. Hypertonic buffer solution induced a decrease of the intracellular pH (pH(i)) of isolated ruminal cells, which is consistent with an inhibition of Na(+)/H(+) exchange, probably isoform NHE-3, because NHE-3-mRNA was detectable in rumen epithelium. These data are in contrast to previous reports and reveal a disturbed Na transport and an impaired barrier function of the rumen epithelium, which predisposes translocation of rumen endotoxins and penetration of bacteria.
authors.affiliation: Forschungsinstitut für die Biologie landwirtschaftlicher Nutztiere-FBN, Forschungsbereich Ernährungsphysiologie Oskar Kellner, Wilhelm-Stahl-Allee, Dummerstorf, Germany.
authors.forename: Monika
authors.initials: M
authors.lastname: Schweigel
authors.forename: Markus
authors.initials: M
authors.lastname: Freyer
authors.forename: Sabine
authors.initials: S
authors.lastname: Leclercq
authors.forename: Benjamin
authors.initials: B
authors.lastname: Etschmann
authors.forename: Ulrike
authors.initials: U
authors.lastname: Lodemann
authors.forename: Almut
authors.initials: A
authors.lastname: Böttcher
authors.forename: Holger
authors.initials: H
authors.lastname: Martens
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002712:Chlorides / Q000378:metabolism; D002857:Chromium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004492:Edetic Acid / Q000378:metabolism; D004594:Electrophysiology; D005260:Female; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000187:drug effects / Q000502:physiology*; D008297:Male; D008353:Mannitol / Q000494:pharmacology; D008839:Microelectrodes; D009994:Osmolar Concentration; D009997:Osmotic Pressure; D010539:Permeability / Q000187:drug effects; D012417:Rumen / Q000187:drug effects / Q000502:physiology*; D012756:Sheep / Q000502:physiology*; D012964:Sodium / Q000378:metabolism*; D017923:Sodium-Hydrogen Exchangers / Q000502:physiology; D013806:Theophylline / Q000494:pharmacology
chemical_list: D002712:Chlorides; D017923:Sodium-Hydrogen Exchangers; D002857:Chromium; D008353:Mannitol; D004492:Edetic Acid; D012964:Sodium; D013806:Theophylline; D000242:Cyclic AMP