Table 1.

Summary of Mechanical and Kinetic Properties of Myofibrils From hiPSC-CMs Following Maximal and Submaximal Ca²⁺ Activation

Myofibril Typea	Tension (mN/mm2)b	kACT (s−1)c	kREL, Slow (s−1)d	tREL, Slow (ms)e	kREL, Fast (s−1)f
pCa 4.0g
Control (n)	18.6 ± 2.5 (26)	0.51 ± 0.04 (23)	0.30 ± 0.04 (25)	192 ± 7.4 (29)	2.66 ± 0.3 (25)
FCM (n)	8.2 ± 1.4 (15)∗∗	0.83 ± 0.13 (14)∗	0.37 ± 0.09 (13)	191 ± 21 (13)	1.69 ± 0.3 (15)∗
pCa 5.8h
Control (n)	8.5 ± 1.4 (22)	0.39 ± 0.06 (22)	0.30 ± 0.03 (17)	154 ± 7.9 (21)	2.47 ± 0.4 (22)
FCM (n)	5.9 ± 1.3 (14)	0.40 ± 0.04 (13)	0.58 ± 0.12 (15)∗	186 ± 17 (14)	2.07 ± 0.4 (15)

^∗p < 0.05; ^∗∗p < 0.01; estimated by Student’s t test.

^aData are means ± SEM. For the comparison with FCM myofibrils, control₁ and control₂ data were merged. N = 3 for each condition.

^bTension, maximal, and submaximal Ca²⁺-activated tension.

^cRate of force generation following Ca²⁺-activation.

^dSlow, rate of the slow isometric phase of relaxation estimated from the normalized slope of the linear fit to the force trace.

^eSlow, duration of the slow isometric phase of relaxation following sudden Ca²⁺ removal.

^fFast, rate of the fast phase of relaxation estimated from the time constant of the exponential fit to the force trace.

^gMaximal activating solution.

^hSubmaximal activating solution.