Aquaporin water channels – from atomic structure to clinical medicine

Abstract

The water permeability of biological membranes has been a longstanding problem in physiology, but the proteins responsible for this remained unknown until discovery of the aquaporin 1 (AQP1) water channel protein. AQP1 is selectively permeated by water driven by osmotic gradients. The atomic structure of human AQP1 has recently been defined. Each subunit of the tetramer contains an individual aqueous pore that permits single-file passage of water molecules but interrupts the hydrogen bonding needed for passage of protons. At least 10 mammalian aquaporins have been identified, and these are selectively permeated by water (aquaporins) or water plus glycerol (aquaglyceroporins). The sites of expression coincide closely with the clinical phenotypes -ranging from congenital cataracts to nephrogenic diabetes insipidus. More than 200 members of the aquaporin family have been found in plants, microbials, invertebrates and vertebrates, and their importance to the physiology of these organisms is being uncovered.

Acute changes in extracellular volume fraction in skeletal muscle monitored by23Na NMR spectroscopy

“…Water not only passively distributes bidirectionally into the extra‐ and intracellular compartments, water channel proteins, so‐called aquaporin, also accelerate the water movement possessing a 10–100‐fold higher capacity for water permeation (Agre et al. 2002). This water flux directed by osmotic and hydraulic gradients is determined by the effective osmotic equilibrium and establishes cell volume.…”

Aquaporins—new players in cancer biology

“…The aquaporins (AQPs) are a family of small (~30 kDa/monomer) membrane transport proteins that assemble in membranes as tetramers and act primarily as water-selective pores, facilitating osmotically driven water transport across cell plasma membranes [1,2]. A subset of the AQP family, the aquaglyceroporins (AQP3, AQP7, AQP9), transport both water and glycerol.…”

Aquaporins in spermatozoa and testicular germ cells: identification and potential role

“…Nonselective water permeability through plasma membranes is very low, as water molecule is polar and diffusion of polar compounds is hindered by lipid bilayers. Aquaporins (AQPs) are water-selective channels which enable a 10-100-fold higher capacity for water transport across plasma membranes (see Agre et al [10]). Among mammalian cells, 13 members of the AQP family have so far been identified, each being predominantly located in different tis-npg sues, and most individual cell types having more than one AQP family member [11,12].…”