(A and C) Normalized representative force traces of the first 15 tetani (100 Hz, 500 ms) separated by 4 seconds, recorded ex vivo from EDL muscles isolated from 6-week-old ClC-1^–/– (blue) and Ca_V1.1^Δe29 ClC-1^–/– (red) mice in the (A) absence and (C) presence of 20 μM verapamil added to the bath. (B and D) Average peak tetanic EDL forces normalized to the initial stimulus, elicited by 44 subsequent 100 Hz, 500 ms tetanic stimulations separated by 4 seconds. EDL muscles were from 6-week-old WT (black, n = 4), ClC-1^–/– (blue, n = 4), Ca_V1.1^Δe29 (orange, n = 4), and Ca_V1.1^Δe29 ClC-1^–/– red, n = 4) mice in the (B) absence and (D) presence of 20 μM verapamil added to the bath for ClC-1^–/– (blue, n = 4) and Ca_V1.1^Δe29 ClC-1^–/– (red, n = 4) EDLs. Dashed lines in D represent the average data presented in B as a reference for pretreatment. (B and D) WT (n = 4; female = 2, male = 2), Ca_V1.1^Δe29 (n = 4; female = 2, male = 2), ClC-1^–/– (n = 4; female = 2, male = 2), Ca_V1.1^Δe29 ClC-1^–/– (n = 4; female = 2, male = 2). Symbols and closed circles indicate the mean ± SEM. (B and D) Statistical significance was determined by 2-way ANOVA with Tukey’s post hoc analysis.