Biological Membranes - A. N. Ogurtsov 2012

Biomembrane Electrogenesis
Mechanisms of Action Potential Generation
Voltage-Gated Potassium Channels

The repolarization process at the beginning of the refractory period is driven primarily by the opening of voltage-gated potassium channels. As a result, the outward potassium ion current surges, the Cytosol loses its excess positive charge, the Membrane Potential reverses back, and the original resting state with a negative membrane potential is restored. In fact, for a very brief period, the membrane even becomes hyperpolarized, reaching the equilibrium potential for potassium ions, which is more negative than the resting membrane potential (Figure 124).

Voltage-gated potassium channels open only upon significant membrane depolarization, meaning they are activated exclusively during The Development of an Action Potential.

Unlike Voltage-Gated Sodium Channels, most voltage-gated potassium channels remain open as long as the membrane stays depolarized, closing only when the membrane potential returns to negative values.

Because these potassium channels do not open immediately at the onset of depolarization, but rather when the action potential reaches its peak, they are referred to as delayed K⁺ channels.

When the membrane returns to its resting state, all voltage-Gated Ion Channels—both sodium and potassium—close. Only unregulated potassium channels remain open, which are responsible for establishing and maintaining the resting membrane potential.