A Current View of the Mammalian Aquaglyceroporins

The discovery of aquaporin water channels by Agre and coworkers answered a long-standing biophysical question of how the majority of water crosses biological membranes. The identification and study of aquaporins have provided insight, at the molecular level, into the fundamental physiology of water balance regulation and the pathophysiology of water balance disorders. In addition to the originally identified classical aquaporins, a second class of aquaporins has been identified. Aquaporins in this latter class, the so-called aquaglyceroporins, transport small uncharged molecules such as glycerol and urea as well as water. Aquaglyceroporins have a wide tissue distribution, and emerging data suggest that several of them may play previously unappreciated physiological or pathophysiological roles. Analyses of transgenic mice have revealed potential roles of aquaglyceroporins in skin elasticity, gastrointestinal function and metabolism, and metabolic diseases such as diabetes mellitus. This review comprehensively discusses the recent discoveries in the field of aquaglyceroporins, alongside a brief overview of the so-called unorthodox aquaporins.