Effects of Bilateral Ureteral Obstruction on Renal Aquaporin Expression

Jeong, Soon Ju; Chung, Sang Young; Nam, Kwang Il; Lee, Seung Won; Park, Sung Sik; Ahn, Kyu Youn

Abstract

BACKGROUND: Obstruction of urinary tract is common cause of renal disfunction. Recent discovery of aquaporin water channels expressed in the kidney and various organs has faciliated our understanding of water transport across the permeable epithelial cell membrane. This study was performed to investigate the effects of bilateral ureteral obstruction on renal expression and cellular distribution of these water channels in rat kidney.
METHODS
Male Sprague-Dawley rats were divided two groups. The abdominal cavity was opened and 2-0 silk ligatures were proximally placed on both ureters in experimental group. Sham-operated group was treated in the same procedures except ligation. After closure of the abdomen, the animals were maintained for 48 hr while being given food and water ad libitum. Kidney sections of both groups were processed for immunohistochemistry using antibodies to aquaporin-1, 2, 3, and 4.
RESULTS
Immunoreactivity for aquaporin-1 of sham-operated kidney was detected in the apical and basolateral plasma membrane of proximal tubules and thin limb of Henle loop. That of bilateral ureteral obstructed kidney was decreased in the both tubules, especially in the proximal tubules and thin limb of Henle loop of inner medulla. Immunoreactivity for aquaporin-2 of sham-operated kidney was the most prominent in apical region and moderate in cytoplasm of the principal cells of entire collecting ducts. That of obstructed kidney was markedly decreased in entire collecting duct, especially inner medulla except inner stripe of outer medulla. The decrease was in parallel between the apical region and cytoplasm. Immunoreactivity for aquaporin-3 of sham-operated kidney was the most prominent in the basolateral plasma membrane of principal cells of entire collecting duct. That of obstructed kidney was decreased in entire collecting duct. Papillary epithelium was stained in obstructed kidney. Immunoreactivity for aquaporin-4 of sham-operated kidney was moderate in the basolateral plasma membrane of principal cells of collecting ducts of inner stripe of outer medulla and inner medulla. In obstructed kidney, immunoreactivity was detected in cortical and outer stripe of outer medullary collecting duct, and decreased in inner stripe of outer medulla and inner medulla. A marked heterogeneity was observed in inner medullary collecting duct.
CONCLUSION
These results indicate that alterations of expression of aquaporin proteins after bilateral ureteral obstruction may lead to change in renal functions, such as urine concentrating ability.