Two hydrophobic loops contain conserved asparagine–proline–alanine ("NPA motif") which form a barrel surrounding a central pore-like region that contains additional protein density.

[4][5] The 2003 Nobel Prize in Chemistry was awarded jointly to Peter Agre for the discovery of aquaporins[6] and Roderick MacKinnon for his work on the structure and mechanism of potassium channels.

[7] Genetic defects involving aquaporin genes have been associated with several human diseases including nephrogenic diabetes insipidus and neuromyelitis optica.

[15][16] Studies by Parisi, Edelman, Carvounis et al. accented not only the importance of the presence of water channels but also the possibility to regulate their permeability properties.

It was present in structures such as kidney tubules and red blood cells, and related to proteins of diverse origins, such as in fruit fly brain, bacteria, the lens of the eye, and plant tissue.

[23] However the first report of protein-mediated water transport through membranes was by Gheorghe Benga and others in 1986, prior to Agre's first publication on the topic.

For example, the aquaporin 3 channel has a pore width of 8–10 Ångströms and allows the passage of hydrophilic molecules ranging between 150 and 200 Da.

However, the water pores completely block ions including protons, essential to conserve the membrane's electrochemical potential difference.

[34] It has been shown that conical entrances with suitable opening angle can indeed provide a large increase of the hydrodynamic channel permeability.

[34] Aquaporin channels appear in simulations to allow only water to pass, as the molecules effectively queue up in single file.

[35] The arrangement of opposite-facing electrostatic potentials in the two halves of the channel prevents the flow of protons but permits water to pass freely.

The most studied aquaporins are compared in the following table: In plants, water is taken up from the soil through the roots, where it passes from the cortex into the vascular tissues.

[42] Aquaporins can play a major role in extension growth by allowing an influx of water into expanding cells - a process necessary to sustain plant development.

[52][53] Specific aquaporins called Large Intrinsic Proteins (LIP)[54] have been found in Heterokonts, including diatoms and brown algae.

Aquaporins have been discovered in the fungi Saccharomyces cerevisiae (yeast), Dictyostelium, Candida and Ustilago and the protozoans Trypanosoma and Plasmodium.

[56][57] Mice with targeted deletions in aquaporin-1 also exhibit a deficiency in water conservation due to an inability to concentrate solutes in the kidney medulla by countercurrent multiplication.

[58] Aquaporins play a key role in acquired forms of nephrogenic diabetes insipidus, disorders that cause increased urine production.

[8] If aquaporin could be manipulated, that could potentially solve medical problems such as fluid retention in heart disease and brain edema after stroke.