How do aquaporins facilitate the passage of water?
Aquaporins are membrane proteins that serve as channels in the transfer of water, and in some cases, small solutes across the cell membrane. The channels are so selective that water passes through them, and acid does not.
They are found in bacteria, plants, and animals.
In mammalian cells, more than 10 forms have been identified so far.
AQP0 is abundant in the lens of the eye.
AQP2 is expressed in the kidney collecting ducts, where it is under the control of antidiuretic hormone (ADH).
Mutations of AQP2 result in diabetes insipidus.
AQP3 is present in the kidney collecting ducts, epidermis, urinary, respiratory, and digestive tracts.
AQP4 is present in the brain astrocytes, eye, ear, skeletal muscle, stomach parietal cells, and kidney collecting ducts.
AQP5 is in the secretory cells such as salivary, lacrimal, and sweat glands.
The diverse and characteristic distribution of aquaporins in the body suggests their important and specific roles in each organ.