The basic job of aquaporin 2 is to reabsorb water from the urine while its being removed from the blood by the kidney. Aquaporin 2 is in kidney epithelial cells and usually lies dormant in intracellular vesicle membranes, but when it is needed vasopressin binds to the cell surface vasopressin receptor, activating a signaling pathway that causes the aquaporin 2 containing vesicles to fuse with the plasma membrane so the aquaporin 2 can be used by the cell.