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 alphaENaC, betaENaC and gammaENaC 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 alphaENaC and betaENaC mRNA abundance on days 1 and 2 preceded sodium retention on days 2 and 3. Conversely, down-regulation of alphaENaC, betaENaC and gammaENaC 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 alphaENaC, betaENaC and gammaENaC proteins were not increased during PAN-induced sodium retention. In conclusion, ENaC mRNA expression, especially alphaENaC, 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.

Background: Nephrotic syndrome (NS) is characterized by renal sodium retention and edema formation. In nephrotic rats the site of enhanced sodium retention has been localized in the cortical collecting duct (CCD). The epithelial sodium channel (ENaC) is the rate-limiting constituent of sodium transport in CCD. Amiloride, an ENaC-blocking drug, corrects the abnormal rate of sodium transport in isolated perfused CCD from puromycin aminonucleoside (PAN)-treated rats. Therefore, we hypothesized that ENaC functional expression is increased in NS. Methods: Unilateral NS was induced by PAN in Wistar rats and analbuminemic Nagase rats (NAR). Urinary protein excretion, renal abundance of mRNA and protein of ENaC subunits, as well as the ENaC regulatory serum glucocorticoid-inducible kinase (Sgk1) and Nedd4-2, were assessed. Results: Proteinuria appeared at day 2 in the Wistar rats and NAR. Surprisingly a downregulation rather than the expected upregulation of α-, β- and γ-ENaC mRNA abundance was observed in both Wistar rats and NAR, when the treated kidney was compared with the untreated kidney. The amount of protein of α-, β- and γ-ENaC was not affected by the NS. Sgk1 mRNA expression did not change and Nedd4-2 protein expression was only decreased at days 1 and 2 in Wistar rats. Conclusion: ENaC mRNA and protein expression are not increased in the early phase of unilateral PAN-induced NS. Sgk1, Nedd4-2 and analbuminemia are not important regulatory factors of ENaC protein expression in experimental NS.

Enhanced abundance of NCC was observed in the initial stage after BDL, followed by a marked decrease. ENaC transcription, translation or cell surface abundance was not increased after BDL.

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 alphaENaC, betaENaC and gammaENaC 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 alphaENaC and betaENaC mRNA abundance on days 1 and 2 preceded sodium retention on days 2 and 3. Conversely, down-regulation of alphaENaC, betaENaC and gammaENaC 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 alphaENaC, betaENaC and gammaENaC proteins were not increased during PAN-induced sodium retention. In conclusion, ENaC mRNA expression, especially alphaENaC, 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.