Tissue Distribution, Expression and Regulation of Urea Transporters.

UT-A and UT-B families of urea transporters consist of multiple isoforms with the majority of the isoforms located in the kidney. UT-B (Slc14A1) in kidney is primarily located in the descending vasa recta. The UT-A (Slc14A2) urea transporter family comprises six distinct isoforms, three of which are predominantly found in the kidney. Specifically, UT-A1 and UT-A3 are located in the inner medullary collecting duct (IMCD), while UT-A2 is situated in the thin descending limb. These transporters play a crucial role in the renal concentration of urine. The regulation of renal urea transporter activity involves acute modifications through phosphorylation and subsequent translocation to the plasma membrane. In response to stimulation by vasopressin or hypertonicity, UT-A1 and UT-A3 accumulate in the IMCD plasma membrane. Chronic regulation of IMCD urea transporters involves hormonal modulation of protein expression levels, such as adrenal steroids, low-protein diets, electrolyte abnormalities, aging or other pathologic conditions. This chapter provides a brief overview of the tissue distribution, expression of the urea transporter isoforms, locations in the kidney, and regulation of urea transporters.