RABBIT DISTAL CONVOLUTED TUBULE COEXPRESSES NACL COTRANSPORTER AND 11-BETA-HYDROXYSTEROID DEHYDROGENASE-II MESSENGER-RNA

Background. Although the renal cortical collecting duct (CCD) is a pri ncipal target for aldosterone, recent evidence suggests that salt tran sport by other nephron segments may also be regulated by aldosterone. Electroneutral and thiazide-sensitive NaCl cotransport by the distal c onvoluted tubule (DCT) of the rat is increased in animals deprived of dietary NaCl. We tested the hypothesis that the DCT of the rabbit is a n aldosterone target tissue. Methods. The single-nephron reverse-trans criptase/polymerase chain reaction (RT-PCR) technique was used to dete rmine mRNA expression of NaCl cotransporter and 11 beta-HSD 2 in disse cted nephron segments. The rabbit NaCl cotransporter was first cloned and rabbit-specific primers selected. A micro-assay was developed to a ssess 11 beta-HSD 2 enzyme activity in 0.5 mm samples of the same neph ron segments. Results. NaCl cotransporter was expressed in 0 of 6 prox imal tubule (PT), 6 of 6 DCT and 3 of 6 CCD samples, while 11 beta-HSD was found in 0 of 7 PT, 7 of 7 DCT and 9 of 9 CCD samples. Corticoste rone was converted to 11-dehydrocorticosterone at a high rate and to a similar extent by both the DCT and CCD, but not the PT. Conclusions. We conclude that the DCT is a target tissue for the action of aldoster one. Axial heterogeneity of electroneutral tin DCT) and electrogenic t in CCD) Na transporters along the distal nephron may improve sodium re covery in low salt and volume states.