Aquaporin 2 is a water transport protein that forms water channels in kidney tubules and plays a predominant role in controlling organism water homeostasis. Members of the aquaporin family are multiple pass transmembrane proteins that form homotetramers to facilitate the flow of water across the plasma membrane. At least thirteen aquaporins have been indentified to date and together this family of small, hydrophobic proteins plays a role in an array of biological processes that include urine formation, cell motility, fertilization, cell junction formation and regulation of overall water homeostasis. AQP2 tetramers form water channels that facilitate water transport and excretion in the kidney. This transport protein is localized to the plasma membrane is response to endocrine signaling. Posterior pituitary hormones arginine vasopressin and ADH regulate osmotic water cell permeability by triggering phosphorylation and subsequent exocytosis of AQP2. Mutations in the corresponding AQP2 gene cause a rare form of diabetes known as nephrogenic diabetes insipidus. This autosomal dominant disorder is characterized by abnormal water reabsorption by kidney tubules due, in part, to either nonfunctional or mislocalized AQP2 protein.
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