Figure 10. Aberrant but distinct calcium transient patterns in DM1- and DM2 iPSC–derived cardiomyocytes.

iPSC-derived cardiomyocytes were labeled with Indo-1 and paced to monitor Ca²⁺ shifts within the cells. (A) Representative Ca²⁺ transient profiles from cardiomyocytes paced at 0.25 Hz derived from healthy control, DM1, and DM2 cardiomyocytes. (B) Average Ca²⁺ transients (paced at 0.25 Hz) from healthy control, DM1, and DM2 cardiomyocyte cell lines. (C) Diastolic Ca²⁺ was reduced in DM2 cardiomyocytes. (D) Peak Ca²⁺ transient amplitude, measured by the difference in peak and diastolic Ca²⁺, was not different across groups. (E and F) The peak rate of Ca²⁺ release (E) and the peak rate of Ca²⁺ reuptake (F) were significantly different in DM2 cardiomyocytes, consistent with altered release and reuptake kinetics compared with healthy control cardiomyocytes. (G–I) Times to peak Ca²⁺ (G), 50% Ca²⁺ release (H), and 50% Ca²⁺ reuptake (I) differed between DM subtypes and healthy control cardiomyocyte cells. Control, 2 cell lines, 33 cell patches; DM1, 2 cell lines, 40 cell patches; DM2, 4 cell lines, 78 cell patches. *P < 0.05, **P < 0.01, ***P < 0.001, ****P < 0.0001, 1-way ANOVA tested at each frequency.