Figure 4. Conduction velocity (CV) is slower in iPSC-CM monolayers from Duchenne Muscular Dystrophy (DMD) hemizygous male and heterozygous female than control.

(a) Activation maps of action potential propagation at 1 Hz. Each color represents a different activation time with time zero appearing in green (¤ indicates the location of the stimuli for each monolayer). White vectors (↑) are a measure of local velocity and direction of the wave. Inset. Representative optical action potentials (APs) at 1 Hz. (b) Bar graphs of CV in each monolayer group, as indicated. Numbers in parenthesis are number of monolayers per group. (c) Averaged 2-ms contour isochrone maps for each representative monolayer above. Tighter averaged isochrone contours in the hemizygous and heterozygous iPSC-CM monolayers indicate slowed and more heterogeneous CV compared to control. (d) CV restitution tended to slow in all groups as pacing frequency increased. (e) Arrhythmias in heterozygous female iPSC-CMs monolayers. Left map, spontaneous pacemaker activity; Left inset, single pixel recording reveals premature ectopic discharges in a pattern of trigeminy; right map, high-frequency reentrant tachycardia maintained by a self-sustaining rotor; right inset, single pixel recording shows the interbeat interval (500 ms) of the reentrant tachycardia. Errors bars represent standard error of the mean (SEM). The n values are in parentheses. Two-tailed Mann–Whitney test. ****p < 0.0001.

Figure 4—figure supplement 1. Conduction velocity in control BJ iPSC-CM (Control 2) monolayer.

(a) Activation maps of action potential propagation at 1 Hz. Each color represents a different activation time with time zero appearing in green (¤ indicates the location of the stimuli for each monolayer). White vectors (↑) are a measure of local velocity and direction of the wave. Inset. Representative optical action potentials (APs) evoked by external stimulation at 1 Hz. (b) Averaged 2-s contour isochrone maps for the representative monolayer in A. (c) Bar graph of conduction velocity in the additional control BJ monolayers. Errors bars represent standard error of the mean (SEM). The n values are in parentheses.

Figure 4—figure supplement 2. Cx43 expression level in control, hemizygous, and heterozygous Duchenne Muscular Dystrophy (DMD) iPSC-CMs.

(a) Typical western blot for connexin43 expression. About 50 k cells were collected to quantify total dystrophin, connexin43, and actinin levels in iPSC-CMs. (b) Scatter plots of Cx43 detected in control, hemizygous, and heterozygous DMD iPSC-CMs. Cx43 protein levels normalized to actinin (loading control) were similar in all tested groups (p = 0.8857 for Male 1, p = 0.6857 for Male 2, and p = 0.1143 for female iPSC-CMs). Two-tailed Mann–Whitney test. Errors bars represent standard error of the mean (SEM). The n values are indicated in parentheses after the name of each group.