Water channel-carrying vesicles in the rat IMCD contain cellubrevin.

Antidiuretic hormone (arginine vasopressin) induces a cyclic process of docking, fusion, and endocytosis of water channel-containing vesicles in the collecting duct. There is now evidence that docking and endocytosis are mediated by an array of proteins associated with vesicles and target membranes. In recent studies, we have shown that cellubrevin, a member of the vesicle-associated membrane protein family, as well as other docking proteins, are expressed in the rat inner medullary collecting duct. We now show by immunogold electron microscopy that cellubrevin is present on vesicles containing water channels, that it is associated with both coated and uncoated vesicles, and that it is present on the apical membrane. Cellubrevin, therefore, is in a position to mediate one or more steps in arginine vasopressin-induced water channel cycling.