(A) Representative recordings of membrane potential showing the smallest amount of depolarizing current needed to evoke an AP (rheobase) at baseline (Ctrl) and after application of retigabine (RTG), XE991 (XE), or retigabine in the presence of XE991 (RTG+XE). (B) Changes in rheobase by application of retigabine (left, n = 14), XE991 (middle, n = 18), or retigabine in the presence of XE991 (right, n = 10). Open symbols and lines indicate the change for individual cells. Filled circles and error bars represent mean ± SEM of the group. *P < 0.001 (paired t test). (C) Quantification of AP threshold obtained from 3 groups of neurons before (Ctrl) and after application of retigabine (RTG, n = 14), XE991 (XE, n = 18), or both retigabine and XE991 (RTG+XE, n = 10). *P = 0.001. **P < 0.001 (paired t test). (D) Left: Averaged number of APs evoked by 1-second depolarizing current as a function of the injected current intensity (defined as fold rheobase) obtained from 5 cells in the absence and presence of 10 μM retigabine, and after washout of the drug (WO). *P = 0.023, and ^#P = 0.01 compared with AP numbers at 2-fold rheobase. **P = 0.008, ^##P = 0.005 between 2 conditions as indicated. Right: Similar plots of data obtained from 9 cells under the control condition and in the presence of 10 μM XE991. *P = 0.002, ^#P < 0.001 compared with AP numbers at 2-fold rheobase. NS: P = 0.4 between 2 groups. Statistical significance was determined by 2-way repeated-measures ANOVA with Holm-Šídák test as a post hoc analysis. (E) Quantification of AP numbers in response to the same suprathreshold stimulation (1 nA for 1 second) obtained from 2 groups of neurons before and after treatment with retigabine, and before and after treatment with XE991, respectively. n = 9 for both groups. *P = 0.01 (paired t test). Box-and-whisker plots in C and E: Horizontal lines of boxes represent 25th percentile, median, and 75th percentile. Whiskers represent 5th/95th percentile. Filled circles represent the mean values.