Figure 3. Increasing the activation rate in kinetic models of Shaker accurately predicts GV and gating current effects. A, Abbreviated form of the 4 × 2-step model (see Class D in Zagotta et al., 1994a) depicting two voltage-dependent conformational changes per subunit before a final, concerted transition. α and γ are forward rate constants (i.e., rate constants of activation) and δ and β are backward rate constants (i.e., rate constants of deactivation). B, Sigmoidicity comparison of individual traces of ShBΔN with and without SSS coexpression. As described by Zagotta et al. (1994b), 11 individual current traces were scaled by normalizing the vertical and horizontal axes so that the maximum current and slope at half-maximum current were the same for each. C, Individual traces depicting patch-clamp recordings of ShBΔN current with and without SSS (black and brown, respectively) overlayed with simulated traces generated from the ZHA two-transition kinetic model of Shaker (red, blue, green). A baseline ZHA trace (red) was established by fitting the model to the pooled ShBΔN trace (brown). No change in forward rate constant α was required to fit the baseline ZHA trace to the slow ShBΔN + SSS trace (slowest black trace). Multiplying α by 1.55 and 2.36 (blue and green, respectively) was needed to match the moderate and fast ShBΔN + SSS traces, respectively. D, GV relationship for ZHA modeled channels based on a previously established rate constant for α compared with values of 1.55α and 2.36α. E, F, ON (E) and OFF (F) gating current traces normalized by total charge movement generated by the ZHA model at baseline and 1.55α. G, Normalized gating current from pooled whole-cell recordings (mean ± SEM) of ShBΔN W434F with and without SSS coexpression upon depolarization to −20 mV. H, Normalized current from pooled whole-cell recordings (mean ± SEM) of ShBΔN W434F with and without SSS coexpression upon repolarization to −100 mV.