Fig. 3: Critical hallmarks of aCM function are retained up to 7 days in culture.

a Ca²⁺ transients of isolated myocytes were recorded to measure time to peak amplitude and time to decay for up 7 days (N = 5). b Peak Ca²⁺ amplitudes were determined up to 7 days in culture (N = 5). c Normalized intracellular reactive oxygen species stain (CellROX) signal was measured over time in culture (N = 3). d Maximal FCCP-uncoupled oxygen consumption rate (OCR) over culture period (N = 3). e Peak contractile forces by spontaneously contracting aCMs were measured on TFM substrates of 2 kPa and 11 kPa stiffness (N = 20 for each treatment). f Electrically stimulated aCMs show a physiological (Bowditch)-resembling force-frequency relationship that scales relative to the absolute force of the cell at f = 1 Hz (N = 5), quadratic fit R² = 0.61. g Peak contractile force measurements measured by TFM in the absence and presence of epinephrine (5 nmol L⁻¹) (N = 5 paired measurements). h Transmission electron microscopy (TEM) at two levels of magnification; scale bars 2 µm. All data expressed as mean ± SEM; N denotes biological replicates; significance indicated by *(p < 0.05), **(p < 0.01), and ***(p < 0.001).