Aquaporins in the vasculature

Water constitutes 70% of the mass of most living organisms. Regulated transport of water is essential to maintaining the proper fluid balance within and between different anatomical compartments. Diffusion of water through the lipid bilayer certainly occurs; however, this low-velocity, high-resistance path is not sufficiently rapid-or regulatable-for many biological processes. Water-specific membrane channel proteins were postulated to exist for several decades, but it was not until 1992 that the first molecular water channel, now called aquaporin-1 (AQP1), was described (1). For discovery of this protein family, as well as for spearheading studies to define the unique structure-function relationships of the molecules, Peter Agre was awarded the Nobel prize in chemistry in 2003. Aquaporins have now been identified at all levels of life, including bacteria, yeast, invertebrates, plants, and animals, a conservation that strongly suggests fundamental roles in a variety of biological processes.