Aquaporins in the Kidney

Water is a major component of the cell, forming between 70 and 95% of its mass. It can cross lipid bilayers of all biological membranes by simple diffusion. However, diffusion is a slow, non-regulated process which cannot account for selective transmembrane water permeation as occurs in many fluid transporting tissues during normal physiological processes. This suggested the existence of additional pathways for water flux. The recent discovery of water channels, Aquaporins (AQPs), provides a molecular explanation for the rapid and regulated transport of water through lipid bilayers1.