Urinary Excretion of Aquaporin-2 in Patients with Diabetes Insipidus

The permeability of the collecting ducts of the kidney to water increases rapidly in response to vasopressin. In what is called the shuttle hypothesis, this increase is believed to be mediated by the movement of a vasopressin-regulated water-channel protein to the apical membranes of the cells of the collecting ducts. 1 – 4 The aquaporins are a family of membrane proteins that function as water-selective channels in many water-transporting tissues. 5 The first aquaporin to be identified, aquaporin-1 (initially termed an aquaporin of channel-forming integral protein), is present in red cells, proximal and descending tubules of the kidney, and other tissues. 6 , 7 We . . .