Verapamil mitigates chloride and calcium bi-channelopathy in a myotonic dystrophy mouse model
Lily A. Cisco, Matthew T. Sipple, Katherine M. Edwards, Charles A. Thornton, John D. Lueck
Lily A. Cisco, Matthew T. Sipple, Katherine M. Edwards, Charles A. Thornton, John D. Lueck
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Research Article Muscle biology

Verapamil mitigates chloride and calcium bi-channelopathy in a myotonic dystrophy mouse model

Abstract

Myotonic dystrophy type 1 (DM1) involves misregulated alternative splicing for specific genes. We used exon or nucleotide deletion to mimic altered splicing of genes central to muscle excitation-contraction coupling in mice. Mice with forced skipping of exon 29 in the CaV1.1 calcium channel combined with loss of ClC-1 chloride channel function displayed markedly reduced lifespan, whereas other combinations of splicing mimics did not affect survival. The Ca2+/Cl– bi-channelopathy mice exhibited myotonia, weakness, and impairment of mobility and respiration. Chronic administration of the calcium channel blocker verapamil rescued survival and improved force generation, myotonia, and respiratory function. These results suggest that Ca2+/Cl– bi-channelopathy contributes to muscle impairment in DM1 and is potentially mitigated by common clinically available calcium channel blockers.

Authors

Lily A. Cisco, Matthew T. Sipple, Katherine M. Edwards, Charles A. Thornton, John D. Lueck

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Figure 4

Verapamil significantly reduces myotonia in both CaV1.1Δe29 ClC-1–/– and ClC-1–/– mouse muscle.

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Verapamil significantly reduces myotonia in both CaV1.1Δe29 ClC-1–/– and...
(A and C) Representative normalized specific force traces of the first (left) and third (right) tetani (150 Hz, 500 ms) from EDL muscles isolated from 6-week-old WT (black) and CaV1.1Δe29 (orange) mice in the (A) absence and (C) presence of 20 μM verapamil added to the bath. Dashed lines represent accumulated force. (B and D) Average integration of normalized specific force for WT (black) and CaV1.1Δe29 (orange) EDL muscles across 3 tetanic stimulations (150 Hz, 500 ms) in the (B) absence and (D) presence of 20 μM verapamil added to the bath. (E and G) Representative normalized specific force traces of the first (left) and third (right) tetani (150 Hz, 500 ms) from EDL muscles isolated from 6-week-old ClC-1–/– (blue) and CaV1.1Δe29 ClC-1–/– (red) mice in the absence (E) and presence (G) of 20 μM verapamil added to the bath. Dashed lines represent accumulated force. (F and H) Average integration of specific force for ClC-1–/– (blue) and CaV1.1Δe29 ClC-1–/– (red) EDL muscles across 3 tetanic stimulations (150 Hz, 500 ms) in the (B) absence and (D) presence of 20 μM verapamil added to the bath. (B, D, F, and H) WT (n = 4; female = 2, male = 2), CaV1.1Δe29 (n = 4; female = 2, male = 2), ClC-1–/– (n = 4; female = 2, male = 2), CaV1.1Δe29 ClC-1–/– (n = 4; female = 2, male = 2). All specific force traces were normalized to the peak specific force. Symbols and open circles represent individual mice; bars indicate the mean ± SEM. Notes: Contralateral EDL muscles were used for each untreated and treated experiment. All traces were plotted with the same scale of time and normalized force for comparison. The same traces without force normalization are shown in Supplemental Figure 8. (B, D, F, and H) **P < 0.01 and ****P < 0.0001, by 1-way ANOVA with Tukey’s post hoc analysis.