ion channel n a cell membrane channel that is selectively permeable to certain ions (as of calcium or sodium)
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a cell membrane protein with an ion-specific transmembrane pore, through which ions and small molecules pass into or out of a cell by diffusion downward along their electrochemical gradient; although some are always open, most open and close in response to a stimulus. Movement of ions through channels controls the electrical potential across the membrane and plays a vital role in depolarization and repolarization of nerve and muscle fibers. Called also protein c.Medical dictionary. 2011.