AQP2, or Aquaporin-2, is a water channel protein found in the kidneys. It plays a crucial role in regulating water balance in the body by facilitating the reabsorption of water from urine back into the bloodstream. This process is essential for maintaining proper hydration and electrolyte levels. The expression and function of AQP2 are influenced by the hormone vasopressin, which is released in response to dehydration. When vasopressin binds to its receptors, it promotes the insertion of AQP2 into the cell membranes of kidney cells, enhancing water reabsorption and concentrating urine.