Submitted on October 8, 2004
Accepted on March 24, 2005
Regulated expression of the renal and intestinal UT-B urea transporter in response to varying urea load
Hideki Inoue1, Shelley D. Kozlowski2, Janet D. Klein2, James L. Bailey2, Jeff M. Sands2, and Serena M. Bagnasco1*
1 Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
2 Renal Division, Department of Medicine, Emory University School of Medicine, Atlanta, GA, USA
* To whom correspondence should be addressed. E-mail: sbagnas1{at}jhmi.edu.
Production, recycling, and elimination of urea are important to maintain nitrogen
balance. Adaptation to varying loads of urea due to different protein intake or in renal
failure, may involve changes in urea transport, and possibly affect urea transporters. In
this study we examine the expression of the UT-B urea transporter in rats fed a low
protein diet (LPD), a high protein diet (HPD), and a 20% urea-supplemented diet. In the
kidney, UT-B protein abundance increased in the outer medulla of both LPD-fed rats and
20% urea-fed rats, without changes in the inner medulla of either group, compared to
controls. In HPD-fed rats UT-B protein decreased significantly in both outer and inner
medulla. We identified expression of UT-B in the rat colon, as a 2 kb mRNA transcript
and as a ~45 kDa protein, with apical localization in superficial colon epithelial cells. UTB
is also expressed in rat small intestine. In rat colon, UT-B protein abundance was
mildly, but significantly, decreased in LPD-fed, and 20% urea-fed rats. UT-B abundance
was also examined in the colon of 7/8 nephrectomized, uremic rats, and in HPD-fed rats,
and was not significantly different from control rats. These findings indicate that UT-B
expression is regulated in response to different loads of urea, with a pattern that
suggests involvement of tissue-specific regulatory mechanism in kidney and colon.
