Modulation of urea transport across sheep rumen epithelium in vitro by SCFA and CO2

American Journal of Physiology. Gastrointestinal and Liver Physiology
Khalid AbdounHolger Martens

Abstract

Urea transport across the gastrointestinal tract involves transporters of the urea transporter-B group, the regulation of which is poorly understood. The classical stimulatory effect of CO(2) and the effect of short-chain fatty acids (SCFA) on the ruminal recycling of urea were investigated by using Ussing chamber and microelectrode techniques with isolated ruminal epithelium of sheep. The flux of urea was found to be phloretin sensitive and passive. At a luminal pH of 6.4, but not at 7.4, the addition of SCFA (40 mmol/l) or CO(2)/HCO3- (10% and 25 mmol/l) led to a fourfold increase in urea flux. The stepwise reduction of luminal pH in the presence of SCFA from 7.4 to 5.4 led to a bell-shaped modification of urea transport, with a maximum at pH 6.2. Lowering the pH in the absence of SCFA or CO(2) had no effect. Inhibition of Na(+)/H(+) exchange increased urea flux at pH 7.4, with a decrease being seen at pH 6.4. In experiments with double-barreled, pH-sensitive microelectrodes, we confirmed the presence of an apical pH microclimate and demonstrated the acidifying effects of SCFA on the underlying epithelium. We confirm that the permeability of the ruminal epithelium to urea involves a phloretin-sensitive pathway. We present cle...Continue Reading

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Citations

Jul 1, 2010·Animal : an International Journal of Animal Bioscience·S Leonhard-MarekH Martens
Jul 3, 2013·Journal of Comparative Physiology. B, Biochemical, Systemic, and Environmental Physiology·F StumpffJ R Aschenbach
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Sep 26, 2015·The Journal of Membrane Biology·J CoyleGavin S Stewart
Jun 13, 2014·American Journal of Physiology. Regulatory, Integrative and Comparative Physiology·Zhongyan LuHolger Martens
Sep 5, 2019·Journal of Animal Physiology and Animal Nutrition·Taylor E NovakSonia J Moisá
Oct 12, 2019·American Journal of Physiology. Gastrointestinal and Liver Physiology·Jack E C KroneDaniel A Columbus
May 28, 2020·Pflügers Archiv : European journal of physiology·Franziska LiebeFriederike Stumpff
Aug 2, 2012·Journal of Animal Science·E C TitgemeyerM L Jones
Jul 27, 2012·American Journal of Physiology. Renal Physiology·David A SpectorKerry J Stewart
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Jan 26, 2020·Journal of Dairy Science·Chongliang ZhongGavin S Stewart
Jun 29, 2010·Journal of Animal Science·A S MuscherK Huber

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