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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

This article has been cited by other articles:

				S. Leonhard-Marek, G. Becker, G. Breves, and B. Schroder Chloride, Gluconate, Sulfate, and Short-Chain Fatty Acids Affect Calcium Flux Rates Across the Sheep Forestomach Epithelium J Dairy Sci, March 1, 2007; 90(3): 1516 - 1526. [Abstract] [Full Text] [PDF]