Aquaporins and water transfer across epithelial barriers.

The cloning and molecular characterization of water channels, generically called aquaporins, have marked a pivotal point in our understanding of water movements across epithelial barriers. Nevertheless, the mechanisms underlying water transfer across these barriers at the molecular and cellular level are not yet clarified. We analyze here the role of the different driving forces moving water across epithelia and the biophysical properties of the water channels. We will also review the recently cloned epithelial members of the aquaporin family, including their expression and distribution in different tissues.