Origins of ion selectivity in potassium channels from the perspective of channel block

Potassium channels play crucial roles in physiology, and one of their more important roles is to repolarize the membrane after an action potential in excitable cells During an action potential, Na + chan nels open first and depolarize the cell membrane, which is followed closely by their inactivation and sub sequent opening of K + channels that repolarize the cell membrane by allowing K + to flow out of the cell. If Na + were allowed to move through K + channels, the influx of Na + would compete with the outflow of K + , and the sharp membrane repolarization would no longer occur. It is then paramount that K + channels select keenly against Na + ions.