Figure 1.

Potassium ion channels are integral membrane proteins that selectively allow potassium ions (K⁺) to pass through the membrane. (a) Ion permeation through the channel involves a pair of K⁺ ions hopping between binding sites in the selectivity filter. The entry of an ion causes ions in the outer configuration (sites 1 and 3) to move outward, expelling an ion and shifting the remaining ions to the inner configuration (sites 2 and 4). The movement of K⁺ across the membrane contributes to various physiological functions, such as repolarizing the membrane after action potentials. (b,c) Voltage-gated potassium channels are composed of four subunits, with six transmembrane segments and a pore-forming P-region. (Adapted from Principles of Neural Science Fifth Edition by Eric R. Kandel and James H. Schwartz and Thomas M. Jessell and Steven A. Siegelbaum and A. J. Hudspeth, McGraw-Hill Companies, New York, USA).