UT-B1 Mediates Transepithelial Urea Flux in the Rat Gastrointestinal Tract

Abstract

The process of urea nitrogen salvaging plays a vital role in the symbiotic relationship between mammals and their intestinal bacteria. The first step in this process requires the movement of urea from the mammalian bloodstream into the gastrointestinal tract lumen via specialized proteins known as facilitative urea transporters. In this study, we examined both transepithelial urea fluxes and urea transporter protein abundance along the length of the rat gastrointestinal tract. Urea flux experiments that used rat gastrointestinal tissues showed significantly higher transepithelial urea transport was present in caecum and proximal colon (P < 0.01, n = 8, analysis of variance [ANOVA]). This large urea flux was significantly inhibited by 1,3,dimethylurea (P < 0.001, n = 8, ANOVA) and thiourea (P < 0.05, n = 6, unpaired t-test), both known blockers of facilitative urea transporters. Immunoblotting analysis failed to detect any UT-A protein within rat gastrointestinal tissue protein samples. In contrast, a 30-kDa UT-B1 protein was strongly detected in both caecum and proximal colon samples at significantly higher levels compared to the rest of the gastrointestinal tract (P < 0.01, n = 4, ANOVA). We therefore concluded that UT-B1 mediates the transepithelial movement of urea that occurs in specific distal regions of the rat gastrointestinal tract.

UT-B Urea Transporter Localization in the Bovine Gastrointestinal Tract

“…This confirms that UT-B2 transporter protein is abundant in papillae throughout the bovine rumen. In contrast, the 30-35 kDa signals expected for UT-B1 protein (Collins et al 2010(Collins et al , 2011Walpole et al 2014) were not detected by hUTBc19, in agreement with the weak UT-B1 transcript expression observed in RT-PCR experiments (Figs. 1, 2).…”

“…Previous studies have shown that UT-B protein is present all along the gastrointestinal tract of both cows (Dix et al 2013) and sheep (Ludden et al 2009), in contrast to observations in rats (Collins et al 2011). In agreement with predictions based on the known regulators of urea transport, the observed ruminant UT-B abundance pattern appeared to be rumen [ small intestine & colon (Dix et al 2013).…”

“…Based upon previous studies in monogastric species (Collins et al 2010(Collins et al , 2011, immunolocalization of UT-B protein to the epithelial cells lining the other parts of the gastrointestinal tract (Fig. 7) was again expected.…”

“…Importantly, this ammonia can then be utilized by the gastrointestinal bacteria as a vital source of nitrogen to enable growth (Lapierre and Lobley 2001). Facilitative UT-B urea transporters play a key role in the urea nitrogen salvaging by mediating the trans-epithelial transport of urea across gastrointestinal tissues (Collins et al 2010(Collins et al , 2011Stewart 2011;Walpole et al 2015).…”

Apoplast Acidification in Growing Barley (Hordeum vulgare L.) Leaves

“…Details of the protocol are given in University but also at UCD using plasma membrane vesicle samples which had been brought back (flight back from Hungary) on dry ice. The Western analyses system at UCD was the same one as described by Collins et al (2011). Red TR / Naphthol AS-MX Tablets (Sigma) following the instructions of the manufacturer.…”