Characteristics of Voltage-gated Ion Channels

Two phases of permeabihty changes may be differentiated depolarization initially leads to an increase in the permeabihty for Na, or Ca. This takes place on a timescale of 0.5 to several hundred miUiseconds. On a timescale of 2 msec to several seconds, the permeability then falls back to the original state. 

The function of the ion channels is determined by the processes of activation and deactivation. 

The process of activation determines duration, size and voltage dependence of the increase in permeability. 

The process of inactivation determines the rate and voltage dependence of the return to the resting state. 

There are thus three states for an ion channel, namely the resting state, activated state and inactivated state. Only the activated state is conducting in the resting state and in the inactivated state, the ion channel is closed. For renewed opening, the ion channel must move from the inactivated state to the resting state. 

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