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1 Faculty of Life Sciences, Medical School, The University of Manchester, Manchester, United Kingdom
2 School of Cellular and Molecular Biosciences, Division of Physiological Sciences, University of Newcastle-upon-Tyne, Newcastle-upon-Tyne, United Kingdom
3 USDA/ARS, U.S. Meat Animal Research Center, Clay Center, NE, USA
* To whom correspondence should be addressed. E-mail: craig.smith{at}manchester.ac.uk.
The UT-A (SLC14a2) and UT-B (SLC14a1) genes encode a family of specialized urea transporter proteins that regulate urea movement across plasma membranes. In this report we describe the structure of the bovine UT-B gene and characterize UT-B expression in bovine rumen. Northern analysis using a full-length bovine UT-B probe detected a 3.7 kb UT-B signal in rumen. RT-PCR of bovine mRNA revealed the presence of two UT-B splice variants, bUT-B1 and bUT-B2, with bUT-B2 the predominant variant in rumen. Immunoblotting studies of bovine rumen tissue, using an antibody targeted to the N-terminus of mouse UT-B, confirmed the presence of 43-54 kDa UT-B proteins. Immunolocalisation studies showed that UT-B was mainly located on cell plasma membranes in epithelial layers of the bovine rumen. Ussing chamber measurements of ruminal trans-epithelial transport of 14C-labelled urea indicated that urea flux was characteristically inhibited by phloretin. We conclude that bUT-B is expressed in the bovine rumen and may function to transport urea into the rumen as part of the ruminant urea nitrogen salvaging process.
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