ion channel

An ion channel is a protein that forms a gated tunnel through the cell membrane, letting charged particles like sodium, potassium, or calcium flow in or out. Think of it as a doorway with a controllable gate: when the gate opens, ions rush through and the cell's electrical state shifts. This flow is how nerves fire and muscles contract.

Channels open and close in response to specific cues, such as a change in membrane voltage, the binding of a messenger molecule, or mechanical stretch. When open, they let huge numbers of ions pass very quickly, and the selectivity filter inside lets only certain ions through. Because the resulting electrical signals govern excitable tissues, channels shape heartbeat, sensation, and thought.

Ion channels are important and sometimes tricky drug targets. Drugs may plug the pore directly, or bind elsewhere on the channel to change how easily it opens. A famous caution in medicinal chemistry is the hERG potassium channel: many unrelated drugs accidentally block it, disturbing the heart's rhythm, so screening against hERG is a routine safety check.