Figure 9.

Forward activation model (Model F). (A) Gating scheme for Model F activation. Four identical resting voltage sensors independently activate with rate α. Pore opening is modeled as a concerted event with rate k_open. Rates susceptible to GxTx are red. (B) Activation sigmoidicity, σ, is plotted for varying α/k_open ratios. Hollow black circles, σ from fit of Eq. 3 to simulations; filled circles, σ values of Kv2.1 experiments from Fig. 3 B, assigned to α/k_open ratios; black, vehicle; red, 1 µM GxTx. (C) The relation of τ_act to the reciprocal of α is plotted for varying α/k_open ratios. Hollow black circles, τ_act from fit of Eq. 3 to simulations; filled circles, τ_act values from Fig. 2 C, assigned to α/k_open ratios by σ in panel B; black, control; red, 1 µM GxTx. (D) Simulated P_open from Model F under control conditions. Light gray, 60 mV; dark gray, 90 mV; black, 120 mV. Dotted lines show fits of Eq. 3. τ_60mV = 6.81 ± 0.01 ms, σ_60mV =1.596 ± 0.003; τ_90mV = 6.196 ± 0.008 ms, σ_90mV = 1.326 ± 0.002; τ_120mV = 5.502 ± 0.004 ms, σ_120mV = 1.141 ± 0.001. (E) Simulated P_open from Model F with GxTx. Light pink, 60 mV; red, 90 mV; dark red, 120 mV. Dotted lines show fits of Eq. 3. τ_60mV = 19.03 ± 0.01 ms, σ_60mV = 3.036 ± 0.003; τ_90mV = 12.35 ± 0.01 ms, σ_90mV = 2.466 ± 0.004; τ_120mV = 9.11 ± 0.01 ms, σ_120mV = 1.958 ± 0.004. (F) Comparison of the reciprocal of k_open from Model F to τ_act from Kv2.1 experiments. Hollow circles or diamonds, mean τ_act from Fig. 2 C; filled circles, k_open⁻¹ from model; black, control; red, 1 µM GxTx. (G) Comparison of the reciprocal of α from Model F to τ_ON from Kv2.1 gating currents. Hollow circles, mean τ_ON from Fig. 8 E; filled circles, α⁻¹ from model; black, vehicle; red, 1 µM GxTx.