In Vitro Analysis and Modification of Aquaporin Pore Selectivity

Aquaporins enable the passage of a diverse set of solutes besides water. Many novel aquaporin permeants, such as antimonite and arsenite, silicon, ammo- nia, and hydrogen peroxide, have been described very recently. By the same token, the number of available aquaporin sequences has rapidly increased. Yet, sequence analyses and structure models cannot reliably predict permeability properties. Even the contribution to pore selectivity of individual residues in the channel layout is not fully understood. Here, we describe and discuss established in vitro assays for water and solute permeability. Measurements of volume change due to flux along osmotic or chemical gradients yield quantitative biophysical data, whereas pheno- typic growth assays can hint at the relevance of aquaporins in the physiological