Consider the chemical exchanges between a muscle cell and the extracellular fluid that bathes it. Sugars, amino acids, and other nutrients enter the cell, and metabolic waste products leave it.
The cell takes in O2 for use in cellular respiration and expels CO2. Also, the cell regulates its concentrations of inorganic ions, such as Na+, K+, Ca2+, and CI-, by shuttling them one way or the other across the plasma membrane.
In spite of heavy traffic through them, cell membranes are selectively permeable, and substances do not cross the barrier indiscriminately. The cell is able to take up some small molecules and ions and exclude others. Also, substances that move through the membrane do so at different rates.
This channel protein, aquaporin, allows entry of up to 3 billion (3 10^9) water molecules per second, passing single file through its central channel which fits ten at a time. (******* thats a lot of molecules - I wonder how much that is in cups?)
Without aquaporins, only a tiny fraction of these water molecules would pass through the same area of the cell membrane in a second, so the channel protein brings about a tremendous increase in rate.
(Engineering human cells to have no aquaporins, so they would die immediately, due to not have nutrients - evil thought - but holy pits if we remove aquaporins in cancer cells or even pathogenic bacterial cells, perhaps we could slowly kill them overtime, because they don't have enough nutrients.)
I believe we could perhaps add more aquaporins to cancer and pathogenic cells in order to flood them with water, causing them to explode, or die due too much liquid - I wonder if that is even possible.