0542. Aquaporins and the kidney

Since water and electrolyte balance are heavily dependent on kidney function it is not surprising to find that of the 10 aquaporins described at this stage at least 7 are expressed at distinct sites in the kidney. Extremely important sites are the proximal convoluted tubule and descending thin loop of Henle which are highly permeable due to AQP1, and the collecting duct where water is tightly regulated by ADH via regulation of AQP2. So-called 'trafficking' of AQP2 to the apical membrane is critical for the reabsorption of water in the collecting ducts, with AQP2 shuttling between intracellular storage sites and the plasma membrane under the control of ADH. There is actually short-term control of water permeability that occurs via the vesicular trafficking mechanism, while long-term permeability is related to the abundance of AQP2 and AQP3 water channels. Mutations of AQP2 and defective trafficking result in nephrogenic diabetes insipidus. ADH/Vasopressin binds to the V2 receptor of AQP2 and cAMP activates a cascade. Phosphorylation of AQP2 is an essential step in regulating vesicle exocytosis - without the necessary stimulus endocytosis occurs and the AQP2 is recycled to the original stores i.e. there is impaired apical shuttling.
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Cell Mol Life Sci 205;62:1692-1706
J Pharmacol Sci 2004; 96: 249-54
Prog Histochem Cytochem 2004; 39: 1-83
Endocrinology 2005 Sep 8 Epub