Oxytocin Induces Apical and Basolateral Redistribution of Aquaporin-2 in Rat Kidney

Title: Oxytocin Induces Apical and Basolateral Redistribution of Aquaporin-2 in Rat Kidney
Authors: Jeon, Un Sil; Joo, Kwon Wook; Na, Ki Young; Kim, Yon Su; Lee, Jung Sang; Kim, Jin; Kim, Gheun-Ho; Nielsen, Soren; Knepper, Mark; Han, Jin Suk
Publisher: Nephron
Date Published: January 01, 2003
Reference Number: 573
The aquaporin-2 (AQP2) water channel is mainly located in the apical plasma membrane of collecting duct epithelial cells, but there has been some evidence of a moderate amount of basolateral localization of AQP2 at least in the inner medullary collecting duct (IMCD). Previous in vitro microperfusion studies showed that oxytocin has an antidiuretic action, most likely mediated by the vasopressin V(2) receptor (V2R) in rat IMCD. By using immunohistochemistry in kidneys from male Sprague-Dawley rats, we observed acute effects of oxytocin on AQP2 localization which were prevented by a V2R antagonist. After intraperitoneal administration of oxytocin (10 U), immunohistochemistry of IMCD revealed that AQP2 was shifted from diffuse cytoplasmic localization in controls to the apical and basolateral membrane domains in oxytocin-treated rats. This pattern of AQP2 redistribution was noted in connecting tubule, cortical collecting duct and outer medullary collecting duct as well as in IMCD, although the tendency to basolateral localization was somewhat less. The pretreatment using a V2R antagonist blocked redistribution of AQP2 in response to oxytocin. We conclude that oxytocin induces a V2R-mediated redistribution of AQP2-containing cytoplasmic vesicles to both apical and basolateral plasma membrane domains in rat kidney. Oxytocin may be one of the factors that accounts for vasopressin-independent AQP2 targeting in the kidney. Copyright 2003 S. Karger AG, Basel

This translation by the NDI Foundation is to assist the lay reader. To provide a clear, accessible interpretation of the original article, we eliminated or simplified some technical detail and complicated scientific language. We concentrated our translation on those aspects of the article dealing directly with NDI. The NDI Foundation thanks the researchers for their work toward understanding and more effectively treating this disorder.
© Copyright NDI Foundation 2007 (JC)

The cell membrane surrounds the cell, forming its perimeter. Researchers refer to the top section of the membrane as the apical membrane, and the bottom and side sections as the basolateral membrane. Aquaporin-2 (AQP2) is a protein, which when triggered by hormone-induced molecular signals, travels from the cell interior to, primarily, the apical membrane. At this location it functions as a channel through which water can cross the cell membrane. AQP2 is found in specific cells that are located in specific areas of the body, notably the principal cells of the kidney collecting duct. When AQP2 is in the membranes of the kidney collecting duct principal cells, it helps the kidney concentrate urine and this helps maintain body water balance.

Vasopressin (AVP) is a hormone that initiates the molecular sequence that sends AQP2 to the apical membrane in kidney collecting duct cells. However, recent studies indicate that factors other than AVP may contribute to the cell’s ability to let water cross its membrane. Jeon, et al., speculated that the hormone, oxytocin, might play a role in redistributing AQP2 from the cell interior to the cell membrane that is independent from AVP. They introduced oxytocin into rats to see the effect on their ability to concentrate urine, then they examined their collecting duct cells to determine the effect of oxytocin on AQP2 movement to the cell membrane.

The research team discovered that oxytocin does help concentrate urine. The researchers also discovered that oxytocin can cause AQP2 to travel from the cell interior to both the apical and basolateral sections of the membrane in the principal cells of the kidney collecting duct and connecting tubule. When the team prevented the vasopressin-2 receptor (V2R) from linking with AVP, oxytocin could not cause the AQP2 to travel to the cell membranes. This suggests that the V2R in some way helps oxytocin to have its translocation effect on AQP2.

The researchers note that AVP, which signals AQP2 to travel to the apical membrane, and oxytocin, which signals it to travel to both the apical and basolateral membrane, must link with the same hormone receptor protein, V2R. They suggest this phenomenon is ripe for further research.