Figure 9.

Schematic diagram illustrating the proposed mechanism of open pore stabilization. (A) Channels in the absence of permeant ions or nonconductive mutant Kv1.2 W366F,V381T have vacant or collapsed selectivity filters. Upon depolarization, the channel activation gate opens, and intracellular ions can enter the inner cavity. Upon hyperpolarization, the pore cannot shut until the inner cavity is vacated, which rate limits the voltage sensor return. (B) In the presence of permeant ions K⁺ or Cs⁺, the selectivity filter is occupied. As the channel pore opens, the hydrated ions can enter the inner cavity, but the binding site is less stable because of strong ion–ion repulsive forces from the other ions in the selectivity filter. Upon hyperpolarization, the exit rate of the hydrated ions is faster as a result of repulsive forces, and the pore can shut faster than in the absence of permeant ions in the conduction pathway. SF, selectivity filter.