The Discovery of Water Channels (Aquaporins)

Abstract

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.

Aging increases the expression of vasopressin receptors in both the kidney and urinary bladder

“…There is increasing evidence that the UBM plays an active role in both solute and fluid reabsorption and is able to modify urine composition . While the underlying biochemical mechanisms have yet to be clarified, it is known that the UBM expresses a variety of receptors and channels including several types of aquaporin water channels and the renal epithelial sodium channel (ENaC), both of which play important roles in vasopressin‐mediated water homeostasis in the kidney . An open question, however, is whether the mammalian UBM also expresses vasopressin receptors and whether expression of vasopressin receptors in the UBM is modified by aging.…”

Pathways for Sensing and Responding to Hydrogen Peroxide at the Endoplasmic Reticulum

“…The physiochemical properties of H 2 O 2 are similar to those of water. Aquaporin (AQP) channels, first established to mediate the diffusion of water across membranes [ 10 , 11 ], have been shown to facilitate transmembrane H 2 O 2 movement [ 12 ]. The mammalian AQP11 has been localized to the ER and established to serve as a “peroxiporin”, facilitating the movement of H 2 O 2 across the ER membrane [ 13 , 14 ].…”

Physical Processes in Polymeric Filters Used for Dialysis

“…Before the discovery of aquaporins it has long been assumed that water can freely penetrate through biological membranes. Then, the existence of family of water channels’ has been proved: it was shown that some membranes of cells are more after permeable than other types of cells as well as pronounced osmotic reaction in comparison with diffusional water permeability [62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87]. This enhanced osmosis water transportation across membranes suggested the existence of special pathways involved in water transfer.…”