Aquaporin 2

AQP2 is found in the apical cell membranes of the kidney's collecting duct principal cells and in intracellular vesicles located throughout the cell.

Regulation
It is the only aquaporin regulated by vasopressin.

This aquaporin is regulated in two ways by the peptide hormone vasopressin:
 * short-term regulation (minutes) through trafficking of AQP2 vesicles to the apical region where they fuse with the apical plasma membrane
 * long-term regulation (days) through an increase in AQP2 gene expression.

Clinical significance
Mutations in this channel are associated with nephrogenic diabetes insipidus, which can be either autosomal dominant or recessive.

Lithium, which is often used to treat bipolar disorder, can cause acquired diabetes insipidus by decreasing the expression of the AQP2 gene. This can result in debilitating increases in the rate of urine production.

The expression of the AQP2 gene is increased during conditions associated with water retention such as pregnancy and congestive heart failure.