The Discovery of Water Channels (Aquaporins)

The movement of water into and out of cells is a fundamental biological process that is essential for life. Such water movement not only regulates the activity of individual cells but also is responsible for the functioning of many organ systems and for maintaining whole body water balance. It had long been suspected that water movement across biological cell membranes was in some way enhanced or facilitated by pores or channels, but the search to identify these channels was long and tedious. As is often the case in science, the secret of the water channel was eventually discovered by chance in 1992 by Peter Agre and his colleagues at the Johns Hopkins University in Baltimore, who were working on red blood cell membrane proteins. This "first" water channel was originally named CHIP28 and is now known as aquaporin 1. Agre received the Nobel Prize in Chemistry in 2003 for this discovery. There are currently 13 known aquaporins in mammals, distributed in most tissues, but many more have been identified in lower organisms and in the plant kingdom. The involvement of aquaporins in processes such as urinary concentration and body fluid homeostasis, brain function, glandular secretion, skin hydration, male fertility, hearing, vision, and most important body functions that can be imagined are now all under intense scientific scrutiny. Moreover, defects in aquaporin function have been related to various disease conditions and pathological states. This brief review will discuss their background, discovery, and function in selected bodily processes, especially focusing on hydration.