Investigation of facilitative urea transporters in the human gastrointestinal tract

The symbiotic relationship between humans and their intestinal microbiomeis supported by urea nitrogen salvaging. Previous studies have shown thatcolonic UT-B urea transporters play a significant role in this important physi-ological process. This current study investigated UT-A and UT-B urea trans-porter expression along the human gastrointestinal tract. Initial end-pointPCR experiments determined that UT-A RNA was predominantly expressedin the small intestine, while UT-B RNA was expressed in stomach, small intes-tine, and colon. Using western blotting experiments, a strong 40–60 kDa UT-B signal was found to be abundant in both ileum and colon. Importantly, thissignal was deglycosylated by PNGaseF enzyme treatment to a core protein of30 kDa in both tissues. Further immunolocalization studies revealed UT-Btransporter proteins were present at the apical membrane of the villi in theileum, but predominantly at the basolateral membrane of the colonic surfaceepithelial cells. Finally, a blind scoring immunolocalization study suggestedthat there was no significant difference in UT-B abundance throughout thecolon (NS, ANOVA,N=5–21). In conclusion, this current study suggestedUT-B to be the main human intestinal urea transporter. Intriguingly, thesedata suggested that the same UT-B isoform was present in all intestinalepithelial cells, but that the precise cellular location varied.