Vasopressin increases Na-K-2Cl cotransporter expression in thick ascendinglimb of Henle's loop

To investigate whether the enhancement of thick ascending limb (TAL) NaCl t ransport in response to long-term increases in circulating vasopressin conc entration is associated with increased expression levels of the apical Na-K -2Cl cotransporter in the rat TAL, we have carried out immunoblotting and i mmunofluorescence studies using affinity-purified, peptide-directed antibod ies. Semiquantitative immunoblotting studies demonstrated a marked increase (193% of controls) in Na-K-2Cl cotransporter band density in response to r estriction of water intake to 15 ml/day for 7 days. In contrast, the expres sion levels of two other apical proteins of the TAL (the type 3 Na/H exchan ger and Tamm-Horsfall protein) were unchanged in the outer medulla. A 7-day subcutaneous infusion of the V-2 receptor-selective vasopressin analog, 1- desamino-[8-D-arginine]vasopressin (DDAVP), to Brattleboro rats also marked ly increased Na-K-2Cl cotransporter expression in the outer medulla (183% o f controls). Immunofluorescence localization in outer medullary tissue sect ions confirmed the increase in Na-K-2Cl cotransporter expression in respons e to DDAVP. We conclude that vasopressin strongly upregulates the expressio n of the Na-K-2Cl cotransporter of the TAL and that it is likely to play an important role in the long-term regulation of the countercurrent multiplic ation system.