Jm. Terris et al., UT-A3: localization and characterization of an additional urea transporterisoform in the IMCD, AM J P-REN, 280(2), 2001, pp. F325-F332
UT-A3 has recently been identified as a splicing variant transcript of the
UT-A gene present in the kidney. To study the cellular and subcellular loca
lization of UT-A3, we raised a new polyclonal antibody to its COOH-terminal
end. Immunoblots identified bands at 44 and 67 kDa predominately in the in
ner medulla and showed that the antibody does not recognize UT-A1. Deglycos
ylation with PNGase decreased the molecular mass of both forms to 40 kDa. U
T-A3 is most abundant in the inner third of the inner medulla and is presen
t in membrane fractions. Cell fractionation studies showed that UT-A3 is on
ly detectable in inner medullary collecting duct (IMCD) cells. These observ
ations were confirmed with immunolocalization studies demonstrating an excl
usive labeling of IMCD cells. Double-labeling studies with anti-Na-K-ATPase
demonstrated UT-A3 in intracellular membranes and in the apical region but
were incompatible with a basolateral site for UT-A3. Although the function
of this isoform in the inner medulla is unknown, the large abundance sugge
sts that it may be important in the renal handling of urea.