ion channel

An ion channel is a tiny gated pore through the cell membrane that lets charged particles — ions such as sodium, potassium, calcium and chloride — flow in or out. Because ion movement creates the electrical signals of nerves, muscle and the heart, controlling these pores is a powerful way for drugs to act, like adjusting the valves that set a cell's electrical rhythm.

As drug targets, ion channels are usually distinguished from ligand-gated channels (which are receptors in their own right). Many channels open and close in response to changes in membrane voltage; these voltage-gated channels for sodium, calcium and potassium underlie nerve impulses, muscle contraction and the heartbeat. Drugs may plug the pore directly or bind nearby to change how easily the channel opens.

Drugs targeting ion channels span many therapeutic areas: local anaesthetics block sodium channels to stop pain signals, calcium-channel blockers relax blood vessels, and several antiepileptics dampen overactive sodium or calcium channels. A key nuance is that many such drugs are 'state-dependent' — they bind more strongly to channels that are firing rapidly, so they preferentially calm overactive tissue while leaving normal activity relatively untouched.