Rabbit distal convoluted tubule coexpresses NaCl cotransporter and 11 beta-hydroxysteroid dehydrogenase II mRNA.
BACKGROUND
Although the renal cortical collecting duct (CCD) is a principal target for aldosterone, recent evidence suggests that salt transport by other nephron segments may also be regulated by aldosterone. Electroneutral and thiazide-sensitive NaCl cotransport by the distal convoluted tubule (DCT) of the rat is increased in animals deprived of dietary NaCl. We tested the hypothesis that the DCT of the rabbit is an aldosterone target tissue.


METHODS
The single-nephron reverse-transcriptase/polymerase chain reaction (RT-PCR) technique was used to determine mRNA expression of NaCl cotransporter and 11 beta-HSD 2 in dissected nephron segments. The rabbit NaCl cotransporter was first cloned and rabbit-specific primers selected. A micro-assay was developed to assess 11 beta-HSD 2 enzyme activity in 0.5 mm samples of the same nephron segments.


RESULTS
NaCl cotransporter was expressed in 0 of 6 proximal 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. Corticosterone 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 aldosterone. Axial heterogeneity of electroneutral (in DCT) and electrogenic (in CCD) Na transporters along the distal nephron may improve sodium recovery in low salt and volume states.
Velázquez
H
H
VA Connecticut Healthcare System West Haven 06516, USA. heinove@ct1.nai.net
Náray-Fejes-Tóth
A
A
Silva
T
T
Andújar
E
E
Reilly
R F
RF
Desir
G V
GV
Ellison
D H
DH
D042842:11-beta-Hydroxysteroid Dehydrogenases; D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002352:Carrier Proteins / Q000235:genetics*; D003001:Cloning, Molecular; D006913:Hydroxysteroid Dehydrogenases / Q000235:genetics*; D007686:Kidney Tubules, Distal / Q000378:metabolism*; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D012333:RNA, Messenger / Q000032:analysis*; D011817:Rabbits; D049992:Sodium Chloride Symporters; D027981:Symporters
D002352:Carrier Proteins; D012333:RNA, Messenger; D049992:Sodium Chloride Symporters; D027981:Symporters; D006913:Hydroxysteroid Dehydrogenases; D042842:11-beta-Hydroxysteroid Dehydrogenases