Impact of changes in inactivation properties on predicted Nav diminution during trains and increases in slow recovery fraction. Underlying assumptions are summarized in the text in association with Fig. 10. Based on Fig. 5 F, fast inactivation in the absence of FGF is ∼0.4 ms. Even if entry into slow recovery is 10-fold slower than normal fast inactivation, it is expected that inactivation will be complete during a 5-ms inactivation step, but that fewer channels will be in slow recovery pathways. (A) Impact of varying A_f (A_s = 1 − A_f) on predicted 1P recovery time course (A1), Nav diminution extent and time course (A2), and 10P recovery (A3). Blue: A_f = 0.95; red: A_f = 0.5; green: A_f = 0.05. Red corresponds to WT CC behavior. (B) As in A, but with predictions based on varying τ_f from 6 ms (blue) to 30 ms (green), with other constants as for WT. (C) As above, but with predictions based on varying τ_s from 200 ms (blue) to 3,000 ms (green) with red similar to WT measurements (600 ms). (D) Predictions based on variation in A_f from 0.95 (blue) to 0.05 (green), but with τ_s = 2,000 ms, highlighting the profound impact of τ_s on cumulative inactivation (D2 and D3).