Water Channel Aquaporins in the Kidney and Salivary Glands

Toshiyuki Matsuzaki^a, Kuniaki Takata^b and Hitoshi Ozawa^a

^aDepartment of Anatomy and Neurobiology, Nippon Medical School
^bDepartment of Anatomy and Cell Biology, Gunma University Graduate School of Medicine

Abstract: Aquaporins are membrane water channel proteins through which water as well as some small solutes permeates the lipid bilayer. So far thirteen isoforms (AQP0-AQP12) have been identified in mammals. They are widely distributed in most water-handling organs. In the kidney, segment-specific expression of AQP1, AQP2, AQP3, AQP4, AQP6, AQP7, and AQP11 in the renal tubular epithelium enables water reabsorption to produce concentrated urine. AQP2 in collecting duct cells translocates between intracellular vesicles and the cell surface via a membrane trafficking mechanism. In salivary glands, AQP5 is present in the apical membrane of the acinar cells and plays an important role in saliva secretion. There are no histochemical data showing the change of the intracellular distribution of AQP5 according to the regulation of water secretion. On the other hand, exocytotic release of secretory granules and following endocytic membrane retrieval cause some change of AQP5-distribution in the membrane. This is a very interesting result to understand the membrane dynamics according to exocytosis and endocytosis.

Key words: aquaporin, water channel, kidney, salivary gland, membrane dynamics