Jb. Wade et al., UT-A2: a 55-kDa urea transporter in thin descending limb whose abundance is regulated by vasopressin, AM J P-REN, 278(1), 2000, pp. F52-F62
The renal urea transporter gene (UT-A) produces different transcripts in th
e inner medullary collecting ducts (UT-A1) and thin descending limbs of Hen
le's loop (UT-A2), coding for distinct proteins. Peptide-directed rabbit po
lyclonal antibodies were used to identify the UT-A2 protein in renal medull
a of mouse and rat. In the inner stripe of outer medulla, an antibody direc
ted to the COOH terminus of UT-A recognized a membrane protein of 55 kDa. T
he abundance of this 55-kDa protein was strongly increased in response to c
hronic infusion of the vasopressin analog 1-deamino-[8-D-arginine]vasopress
in (DDAVP) in Brattleboro rats, consistent with previous evidence that UT-A
2 mRNA abundance is markedly increased. Immunofluorescence labeling with th
e COOH-terminal antibody in Brattleboro rats revealed labeling in the lower
portion of descending limbs from short-looped nephrons (in the aquaporin-1
-negative portion of this segment). This UT-A labeling was increased in res
ponse to DDAVP. Increased labeling was also seen in descending limbs of lon
g-looped nephrons in the base of the inner medulla. These results indicate
that UT-A2 is expressed as a 55-kDa protein in portions of the thin descend
ing limbs of Henle's loop and that the abundance of this protein is strongl
y upregulated by vasopressin.