Ion channel: A protein that acts as a pore in a cell membrane and permits the selective passage of ions (such as potassium ions, sodium ions, and calcium ions), by means of which electrical current passes in and out of the cell. Ion channels also serve many other critically important functions including chemical signalling, transcellular transport, regulation of pH, and regulation of cell volume. Malfunction of ion channels can cause diseases in many tissues. The array of human diseases associated with defects in ion channels is growing. These diseases are called channelopathies.
The 2003 Nobel Prize in Chemistry was awarded jointly to Peter Agre and Roderick MacKinnon for their studies of the "tiny transportation tunnels" in cell walls. Dr. Agre, at Johns Hopkins University in Baltimore, discovered in 1988 the channels that let water pass in and out of cells while Dr. MacKinnon, at the Rockefeller University in New York, described in 1998 the first detailed structure of an ion channel.