Figure 2.

Properties and output of the simplified model. (A) (a) shows a sketch of the voltage sensor domain considered in the simplified model, with the gating pore and two adjacent vestibules. The dashed lines represent surfaces used to divide the space into subvolumes. (b)–(d) are plots of the position-dependent gating charge density, anion and cation concentrations, and electrostatic potential, assessed at 0 mV of applied potential. The concentration and electrostatic potential profiles are shown for two different positions of the voltage sensor (solid and dashed lines, respectively). Notice that at the ion concentrations reached, only a few ions will be present inside the vestibule at each time. (B) Plot of the ionic net charge in the left compartment (bath and vestibule) as a function of the position of the voltage sensor. The two positions labeled “1” and “2” correspond to the two positions of the voltage sensor considered in (A). (C) Electrostatic, chemical, and total (electrostatic + chemical) energy profiles experienced by the voltage sensor during its movement through the gating pore. As stated in the text, in The simplified model, we arbitrarily choose the energy profile experienced by the particle. This profile contains the overall energy charges experienced by the sensor, including the electrostatic voltage profile created by the voltage sensor and ions, and all other kinds of chemical and electrostatic interaction with the voltage sensor domain. (D) Trial simulation performed with our simplified model, using the energy profile shown in (Cd) and a friction coefficient of 2 × 10⁻⁶ kg/s. From top to bottom, the panel shows the position of the voltage sensor (i.e., of the gating charge) from the center of the gating pore, the unfiltered gating current produced by the movement of the voltage sensor, and the same gating current filtered with a digital, eight-pole Bessel filter with a cutoff frequency of 8 kHz. The red line in the top panel represents the energy profile encountered by the voltage sensor. It is superimposed on the time course of the voltage sensor position to show that the voltage sensor spends most of its time in the energy wells present in the two vestibules (we used the same graphic style used by (6) to make comparisons with earlier work easier). To see this figure in color, go online.