Fig. 1.

The “three-click” model (Left) is a logical extrapolation to H_V1 of S4 movement during K⁺ or Na⁺ channel opening. The three Arg (R) in the S4 helix all move outward past the yellow hydrophobic gasket, from intracellular to extracellular aqueous vestibules. In the new “one-click” model (Right), Li et al. (3) propose that S4 moves only one turn of the helix upwards.