voltage-gated ion channel

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voltage-gated ion channel Any ion channel that opens and closes in response to changes in electrical potential across the cell membrane in which the channel is situated. There are several types of voltage-gated channel, each allowing the selective passage of a particular ion. Two types are especially important in transmitting action potentials along axons: voltage-gated sodium channels and voltage-gated potassium channels. The sodium channels open rapidly in response to initial depolarization of the axon plasma membrane, allowing sodium ions (Na+) to flood in. Depolarization also triggers less rapid opening of the potassium channels, which permits outflow of potassium ions (K+), thus acting to restore the membrane potential to its resting state. Voltage-dependent calcium channels also carry some of the depolarizing current in some cells. The sodium channel protein has positively charged voltage-sensing regions, which move towards negative charges on the outer surface of the membrane when the latter becomes depolarized. This opens the channel, allowing passage of sodium ions. Within a millisecond of channel opening, the voltage-sensing region returns to its original location, and a channel-inactivating segment moves to block the channel and allow the channel protein to revert to its resting state.