|Smith, Timothy - Tim|
Submitted to: American Journal of Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/12/2005
Publication Date: 7/3/2005
Citation: Stewart, G.S., Grahman, C., Cattell, S., Smith, T.P., Simmons, N.L., Smith, C.P. 2005. UT-B is expressed in bovine rumen: potential role in ruminal urea transport. American Journal of Physiology. 289:605-612. Interpretive Summary: The bovine UT-B protein is a member of a family of specialized urea transporter proteins that regulate urea movement across cell membranes. Urea nitrogen is an important component of animal waste, and nitrogen secretion from the animal impacts waste management. In the bovine digestive tract, a process known as nitrogen "salvaging" can occur that permits the animal to use nitrogen in urea as a building block for protein synthesis and hence allows the nitrogen to improve meat production efficiency while decreasing animal waste. This study characterizes the bovine SLC14A1 gene that produces the UT-B urea transporter, and shows that it is a functional participant in the nitrogen salvaging process.
Technical Abstract: 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.