Hyperosmolality regulates UT‐A6 urea transporter expression in the Caco‐2 cell line

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.