Genetic defects involving aquaporin genes have been associated with several human diseases. The 2003 Nobel Prize in Chemistry was awarded jointly to Peter Agre for the discovery of aquaporins, and Roderick MacKinnon for his work on the structure and mechanism of potassium channels. The cell membranes of a variety of different animal and plant cells contain aquaporins through which water can flow more rapidly inside the cell than by diffusing through the phospholipid bilayer.

Aquaporins are "the plumbing system for cells," said Agre. Every cell is primarily water. "But the water doesn’t just sit in the cell, it moves through it in a very organized way. The process occurs rapidly in tissues that have these aquaporins or water channels."

For many years, scientists assumed that water leaked through the cell membrane, and some water does. "But the very rapid movement of water through some cells was not explained by this theory," said Agre.

Aquaporins selectively conduct water molecules in and out of the cell, while preventing the passage of ions and other solutes. Also known as water channels, aquaporins are integral membrane pore proteins. Some of them, known as aquaglyceroporins, also transport other small uncharged solutes, such as glycerol, CO₂, ammonia and urea across the membrane, depending on the size of the pore. For example, the aquaporin 3 channel has a pore width of 8-10 Ångströms and allows the passage of hydrophilic molecules ranging between 150-200 Da. However, the water pores are completely impermeable to charged species, such as protons, a property critical for the conservation of the membrane's electrochemical potential difference.

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