Regulation of aquaporins and sodium transporter proteins in the solitary kidney in response to partial ureteral obstruction in neonatal rats

Abstract

Unilateral ureteral obstruction (UUO) impairs function of the obstructed kidney, and the contralateral nonobstructed kidney compensates depending on the degree and duration of UUO. This study aimed to determine the hemodynamic and molecular changes in the solitary kidney in response to partial ureteral obstruction (PUO) where any compensation from the contralateral kidney was eliminated so that all observed changes in the kidney tissue occurred in the kidney with PUO. Newborn rats were subjected to unilateral left nephrectomy (UNX) within the first 48 h of life and a subset of UNX rats was subjected to severe PUO of the right kidney at day 14. Renal blood flow and whole kidney volume were measured with MRI at week 10. The renal protein abundance of aquaporin 1 (AQP1), AQP2 and AQP3 as well as Na,K-ATPase, NaPi-2 (type 2 sodium-phosphate cotransporter) and NHE3 (type 3 sodium-proton exchanger) were examined by immunoblotting and immunocytochemistry. At 10 weeks of age, the protein abundance of AQP2, AQP3, Na,K-ATPase, NaPi-2 and NHE3 were increased in response to PUO. In contrast, AQP1 expression was markedly decreased compared to sham-operated rats. These findings were confirmed by immunohistochemistry. GFR, urine osmolality and urine sodium excretion were reduced and kidney weight increased in response to PUO. In conclusion, the present study demonstrated major changes in the protein abundance of renal AQP1, AQP2 and AQP3 and sodium transporters in the solitary PUO kidney. These changes were paralleled by decreased urinary sodium excretion and a significant reduction in urinary osmolality from the obstructed kidney, suggesting a functional association between the molecular changes and the ability of the obstructed kidney to handle sodium and water in this solitary kidney model.