Differential Expression and Function of Urea Transporters in Rat and Human Colon

Abstract

Gastrointestinal urea transporters play a significant role in urea nitrogen salvaging (UNS) processes between mammalian hosts and gut bacteria. In regions of high bacterial populations (proximal colon), urea is secreted into the colonic lumen and used as a nutrient source by commensal bacteria. Although urea transporters are expressed in human colon, their functional relevance remains to be elucidated. The aim of this study was to investigate expression and function of the facilitative urea transporter UT-B in rat and human colon. Immunoblot analysis demonstrated expression of a 35 kDa glycosylated UT-B protein in colonic mucosa with significantly higher expression in right colon compared to left (P<0.01, N=3). This glycosylated UT-B protein was predominantly located in plasma membrane-enriched samples (P<0.001, N=6). Urea flux studies performed in rat and human colon mounted in Ussing chambers demonstrated higher urea flux in right compared to left colon(P<0.05, N=6). In addition, bi-directional urea flux in right colonic specimens was sensitive to the urea transporter inhibitor, 1,3, dimethylurea (DMU) (P<0.05,N=6). This study demonstrates differential expression and function of UT-B transporters in rat and human colon suggesting that urea transport is an important process in the symbiotic relationship between gut commensal bacteria and their mammalian hosts.