Investigation of facilitative urea transporters in the human gastrointestinal tract.

The symbiotic relationship between humans and their intestinal microbiome is supported by urea nitrogen salvaging. Previous studies have shown that colonic UT-B urea transporters play a significant role in this important physiological process. This current study investigated UT-A and UT-B urea transporter expression along the human gastrointestinal tract. Initial end-point PCR experiments determined that UT-A RNA was predominantly expressed in the small intestine, while UT-B RNA was expressed in stomach, small intestine, 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, this signal was deglycosylated by PNGaseF enzyme treatment to a core protein of 30 kDa in both tissues. Further immunolocalization studies revealed UT-B transporter proteins were present at the apical membrane of the villi in the ileum, but predominantly at the basolateral membrane of the colonic surface epithelial cells. Finally, a blind scoring immunolocalization study suggested that there was no significant difference in UT-B abundance throughout the colon (NS, ANOVA, N = 5-21). In conclusion, this current study suggested UT-B to be the main human intestinal urea transporter. Intriguingly, these data suggested that the same UT-B isoform was present in all intestinal epithelial cells, but that the precise cellular location varied.