Abstract
Gastrointestinal facilitative urea transporters play a significant role in the urea nitrogen salvaging process, which supports the symbiotic relationship between mammals and their gut microbial populations. UT‐A6 urea transporters have been previously reported in the human gastrointestinal tract, specifically in the colon. As renal UT‐A transporters can be regulated by external osmolality, this study investigated whether UT‐A6 expression could also be regulated in this manner. Initial end‐point RT‐PCR experiments confirmed UT‐A6 expression along the human gastrointestinal tract (colon > small intestine ≫ stomach) and also in the Caco‐2 intestinal cell line. Using Caco‐2 cells exposed for 24 hours to changed external osmotic conditions (from 350 to 250, 500, or 600 mOsm), end‐point PCR suggested UT‐A6 expression increased in hyperosmotic conditions. Using quantitative PCR, it was confirmed that 24 h exposure to 600 mOsm stimulated a significant ~15‐fold increase in UT‐A6 expression (P < 0.001, N = 5, ANOVA). Finally, inhibitory experiments suggested that protein kinase C and calcium were involved in this hyperosmotic‐stimulated regulatory pathway. In conclusion, these data demonstrated UT‐A6 expression was indeed regulated by external osmolality. The physiological significance of this regulatory process upon gastrointestinal urea transport has yet to be determined.
Highlights
Mammalian facilitative urea transporters (UTs), encoded by either Slc14a1 (UT-B) or Slc14a2 (UT-A) genes, facilitate the movement of urea across plasma cell membranes (Stewart 2011)
Using cDNA derived from adult colon total RNA, pooled from five donors, signals for UT-A6 were detected at sizes of 128 and 136 bp as expected
UT-A6 was characterized as a unique urea transporter located in human colon (Smith et al 2004)
Summary
Mammalian facilitative urea transporters (UTs), encoded by either Slc14a1 (UT-B) or Slc14a2 (UT-A) genes, facilitate the movement of urea across plasma cell membranes (Stewart 2011). Gastrointestinal urea transporters play a significant role in the urea nitrogen salvaging process, which supports the symbiotic relationship between mammals and the microbial populations within their gastrointestinal tract (Stewart and Smith 2005). Functional UT-B urea transporter proteins have been detected in bovine rumen (Stewart et al 2005), human colon (Collins et al 2010), rat colon (Collins et al 2011), and in the Caco-2 intestinal cell line (Inoue et al 2004). UT-A6 is a unique UT-A urea transporter that has been detected in the human colon (Smith et al 2004). Northern blot analysis showed UT-A6 to be expressed in human colon, but not stomach or small intestine (Smith et al 2004)
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