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This Article Full Text Full Text (PDF) All Versions of this Article: 291/2/G246    most recent 00419.2005v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Web of Science (1) Citing Articles via Google Scholar Google Scholar Articles by Leonhard-Marek, S. Articles by Busche, R. Search for Related Content PubMed PubMed Citation Articles by Leonhard-Marek, S. Articles by Busche, R.

MUCOSAL BIOLOGY

Effect of chloride on pH microclimate and electrogenic Na⁺ absorption across the rumen epithelium of goat and sheep

¹Department of Physiology and ²Department of Biochemistry, School of Veterinary Medicine, Hannover, Germany

Submitted 6 September 2005 ; accepted in final form 10 February 2006

Active Na⁺ absorption across rumen epithelium comprises Na⁺/H⁺ exchange and a nonselective cation conductance (NSCC). Luminal chloride is able to stimulate Na⁺ absorption, which has been attributed to an interaction between Cl^–/HCO₃^– and Na⁺/H⁺ exchangers. However, isolated rumen epithelial cells also express a Cl^– conductance. We investigated whether Cl^– has an additional effect on electrogenic Na⁺ absorption via NSCC. NSCC was estimated from short-circuit current (I_sc) across epithelia of goat and sheep rumen in Ussing chambers. Epithelial surface pH (pH_s) was measured with 5-N-hexadecanoyl-aminofluorescence. Membrane potentials were measured with microelelectrodes. Luminal, but not serosal, Cl^– stimulated the Ca²⁺ and Mg²⁺ sensitive I_sc. This effect was independent of the replacing anion (gluconate or acetate) and of the presence of bicarbonate. The mean pH_s of rumen epithelium amounted to 7.47 ± 0.03 in a low-Cl^– solution. It was increased by 0.21 pH units when luminal Cl^– was increased from 10 to 68 mM. Increasing mucosal pH from 7.5 to 8.0 also increased the Ca²⁺ and Mg²⁺ sensitive I_sc and transepithelial conductance and reduced the fractional resistance of the apical membrane. Luminal Cl^– depolarized the apical membrane of rumen epithelium. 5-Nitro-2-(3-phenylpropylamino)-benzoate reduced the divalent cation sensitive I_sc, but only in low-Cl^– solutions. The results show that luminal Cl^– can increase the microclimate pH via apical Cl^–/HCO₃^– or Cl^–/OH^– exchangers. Electrogenic Na⁺ absorption via NSCC increases with pH, explaining part of the Cl^– effects on Na⁺ absorption. The data further show that the Cl^– conductance of rumen epithelium must be located at the basolateral membrane.

electrolyte transport; sodium absorption; forestomach; ruminants; microclimate

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