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Clinical Science (2003) 104, (389–395) (Printed in Great Britain)
Epithelial sodium channel (ENaC) subunit mRNA and protein expression in rats with puromycin aminonucleoside-induced nephrotic syndrome
A. AUDIGÉ, Z.R. YU, B.M. FREY, D.E. UEHLINGER, F.J. FREY and B. VOGT
Division of Nephrology and Hypertension, Inselspital, University of Berne, Freiburgstrasse 3, 3010 Berne, Switzerland
Key words: aldosterone, epithelial sodium channel, nephrotic syndrome, puromycin aminonucleoside, real-time PCR, Western blot. Abbreviations: CCD, cortical collecting duct; CT, threshold cycle; ENaC, epithelial sodium channel; GAPDH, glyceraldehyde-3-phosphate dehydrogenase; PAN, puromycin aminonucleoside; RT, reverse transcription. Correspondence: Dr Bruno Vogt (e-mail bruno.vogt@insel.ch). 
In experimental nephrotic syndrome, urinary sodium excretion is decreased during the early phase of the disease. The molecular mechanism(s) leading to salt retention has not been completely elucidated. The rate-limiting constituent of collecting duct sodium transport is the epithelial sodium channel (ENaC). We examined the abundance of ENaC subunit mRNAs and proteins in puromycin aminonucleoside (PAN)-induced nephrotic syndrome. The time courses of urinary sodium excretion, plasma aldosterone concentration and proteinuria were studied in male Sprague–Dawley rats treated with a single dose of either PAN or vehicle. The relative amounts of aENaC, bENaC and gENaC mRNAs were determined in kidneys from these rats by real-time quantitative TaqMan PCR, and the amounts of proteins by Western blot. The kinetics of urinary sodium excretion and the appearance of proteinuria were comparable with those reported previously. Sodium retention occurred on days 2, 3 and 6 after PAN injection. A significant up-regulation of aENaC and bENaC mRNA abundance on days 1 and 2 preceded sodium retention on days 2 and 3. Conversely, down-regulation of aENaC, bENaC and gENaC mRNA expression on day 3 occurred in the presence of high aldosterone concentrations, and was followed by a return of sodium excretion to control values. The amounts of aENaC, bENaC and gENaC proteins were not increased during PAN-induced sodium retention. In conclusion, ENaC mRNA expression, especially aENaC, is increased in the very early phase of the experimental model of PAN-induced nephrotic syndrome in rats, but appears to escape from the regulation by aldosterone after day 3.
Received 19 August 2002/20 December 2002; accepted 24 January 2003
The Biochemical Society and the Medical Research Society © 2003 |
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