Drug targets on cell membrane. Illustration of the mechanism of action for drugs that act on structures embedded in a cell membrane (phospholipid bilayer, pink). At centre is an ion channel, with another channel at left. Other examples of such channels include membrane carrier proteins and ion pumps. Such proteins, embedded in the cell membrane, act as channels for ions (purple spheres) and other chemicals (green) moving into and out of a cell. Biochemical signals prompt the opening and closing of the channels, but this can be disrupted by drugs (blue) that bind to the channels.