aquaporin

noun

aqua·​por·​in ˌa-kwə-ˈpȯr-ən 

: any of several proteins that are found in cell membranes and selectively permit water to pass into and out of the cell

Several scientific groups are now directing their attention to the aquaporins, a large family of water transport molecules whose members each have unique tissue distributions in kidney.

—Peter Agre, Proceedings of the National Academy of Science

Water passes through the cell membrane via channels called aquaporins. These channels are so small that water molecules travel through in single file, while larger molecules cannot enter.

—Julie Rehmeyer, New Scientist