title: Short communication: Effects of dietary nitrogen concentration on messenger RNA expression and protein abundance of urea transporter-B and aquaporins in ruminal papillae from lactating Holstein cows.
abstract: To test the hypothesis that dietary N concentrations affect gut epithelial urea transport by modifying the expression of urea transporter B (UT-B) and aquaporins (AQP), the mRNA expression and protein abundance of UT-B and AQP3, AQP7, AQP8, and AQP10 were investigated in ruminal papillae from 9 lactating dairy cows. Ruminal papillae were harvested from cows fed low N (12.9% crude protein) and high N (17.1% crude protein) diets in a crossover design with 21-d periods. The mRNA expression was determined by real-time reverse transcription-PCR and protein abundance by immunoblotting. The mRNA expression of UT-B was not affected by dietary treatment, whereas mRNA expression of AQP3, 7, and 10 were greater in the high N compared with the low N fed cows. Using peptide-derived rabbit antibodies to cow AQP3, 7, and 8, immunoblotting revealed bands of approximately 27, 27, and 24 kDa in ruminal papillae, respectively. A peptide-derived chicken antibody to cow UT-B detected a band of approximately 30 to 32 kDa in ruminal papillae. The abundance of UT-B and AQP3 and 7 were not affected by dietary treatment. In contrast, the abundance of AQP8 was greater in high N compared with low N diets. In conclusion, AQP3, 7, and 8 were found to be expressed in bovine rumen papillae. None of the investigated transcripts or proteins correlated to the increased rumen epithelial urea permeability observed with low dietary N concentration.
authors.affiliation: Department of Animal Health and Bioscience, Faculty of Agricultural Sciences, Aarhus University, DK-8830 Tjele, Denmark.
authors.forename: B A
authors.initials: BA
authors.lastname: Røjen
authors.forename: S B
authors.initials: SB
authors.lastname: Poulsen
authors.forename: P K
authors.initials: PK
authors.lastname: Theil
authors.forename: R A
authors.initials: RA
authors.lastname: Fenton
authors.forename: N B
authors.initials: NB
authors.lastname: Kristensen
mesh_terms: D000818:Animals; D020346:Aquaporins / Q000378:metabolism*; D002417:Cattle / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D005260:Female; D007774:Lactation; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009584:Nitrogen / Q000008:administration & dosage*; D012333:RNA, Messenger / Q000378:metabolism*; D012417:Rumen / Q000378:metabolism*; D013045:Species Specificity; D000096982:Urea Transporters
chemical_list: D020346:Aquaporins; D026901:Membrane Transport Proteins; D009584:Nitrogen; D012333:RNA, Messenger; D000096982:Urea Transporters