UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract.

Facilitative UT-B urea transporters play an important role in the urea nitrogen salvaging process that occurs in the gastrointestinal tract of mammals, particularly ruminants. Gastrointestinal UT-B transporters have previously been reported in various ruminant species-including cow, sheep and goat. In this present study, UT-B transporter localization was investigated in tissues throughout the bovine gastrointestinal tract. RT-PCR analysis showed that UT-B2 was the predominant UT-B mRNA transcript expressed in dorsal, ventral and cranial ruminal sacs, while alternative UT-B transcripts were present in other gastrointestinal tissues. Immunoblotting analysis detected a strong, glycosylated ~50 kDa UT-B2 protein in all three ruminal sacs. Immunolocalization studies showed that UT-B2 protein was predominantly localized to the plasma membrane of cells in the stratum basale layer of all ruminal sac papillae. In contrast, other UT-B protein staining was detected in the basolateral membranes of the surface epithelial cells lining the abomasum, colon and rectum. Overall, these findings confirm that UT-B2 cellular localization is similar in all ruminal sacs and that other UT-B proteins are located in epithelial cells lining various tissues in the bovine gastrointestinal tract.