Publikationsdatenbank

Urea transport across the rumen epithelium is electrically silent and modulated by changes in pH (2007)

Art

Poster

Autoren

Abdoun, K

Stumpff, F

Martens, H

Kongress

European Intestinal Transport Group

Oberwiesenthal, 03. – 06.03.2007

Quelle

Journal of Physiology and Biochemistry

Seiten: 32

ISSN: 1138-7548

Sprache

Englisch

Kontakt

Institut für Veterinär-Physiologie

Oertzenweg 19 b
14163 Berlin
+49 30 838 62600
physiologie@vetmed.fu-berlin.de

Abstract / Zusammenfassung

Background: Urea transferred from the blood to the digestive tract of ruminants and non-ruminants is a potentially important source of N for microbial growth in the gut (1), serving as a significant source of N when dietary intake is low. Recent studies have demonstrated urea transporter (UT) mRNA and protein in the rumen and colon epithelium of sheep (2) and cows (3). In this study, we investigated if urea flux across the rumen epithelium occurs paracellularly or transcellulary, and if there are indications for electrogenic cotransport.
Methods: Urea flux across sheep rumen epithelia was studied in Ussing-chambers. Isolated cells were monitored for effects of urea using the patch clamp technique.
Results: The Ussing chamber and patch clamp data did not show any impact of urea on transepithelial current, tissue conductance, transmembrane current or cell capacitance. Likewise, transepithelial potential had no impact on urea fluxes and no correlation with mannitol flux could be found. Conversely, reducing the mucosal pH from 7.4 to 6.4 resulted in an almost seven-fold increase in the serosal to mucosal urea flux rates, without affecting the mannitol flux in the same direction. Addition of amiloride to the mucosal side enhanced urea transport across the epithelium in a dose dependent manner, with a maximal rate of transport seen at a dose of 0.6 mmol/l.
Conclusion: The data suggest that transport of urea across the rumen epithelium involves an electrically silent mechanism. The response to variation of intracellular and extracellular pH suggests a mainly transcellular pathway, the exact nature of which remains to be determined.

1) Kennedy, PM; Milligan, LP (1980). Can. J. Anim. Sci. 60: 205-221.
2) Ritzhaupt, A; Wood, IS; Jackson, A.A.; Moran, JB; Shirazi-Beechey, PS (1998). Biochem. Soc. Trans. 26: S122.
3) Stewart GS; Graham C; Cattell S; Smith TPL; Simmons NL; Smith, CP (2005). Am. J. Physiol. 289: R605?R612.
Grants: Margarete-Markus-Charity; Alexander von Humboldt Foundation