Figure 2.

Potassium channels help regulate the electrical excitability of cells, control the duration and frequency of action potentials, and maintain the resting membrane potential. (d) A voltage-gated potassium channel subunit contains six transmembrane α-helixes (S1–S6), a short α-helix (the P helix), as well as an α-helix on the cytoplasmic side of the membrane that connects transmembrane helixes S4 and S5 (4–5). (e) Side view of the tetrameric voltage-gated potassium channel. (f,g) Voltage-gated potassium channels open or close in response to changes in the membrane potential, the S1–S4 voltage-sensing domain shifts between the external and internal halves of the membrane, influencing the movement of the S4–S5 coupling helix. (h,i) In voltage-gating, membrane repolarization makes the S4–S5 coupling helix move downward, the S6 inner helix bends at its glycine hinge to close the channel gate. (j,k) In the closed state, the inner helices of the pore are too narrow for K+ to pass through. In the open state, these helices bend and widen the pore to allow ion flow through it. (l) Potassium ion channels are highly selective for K⁺ over other ions, the permeability of them is determined by the interaction of ions with water, the membrane lipid bilayer, and ion channels. (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).