Table 3. Force measurements in donor cardiomyocytes after exchange with recombinant troponin without PKA treatment.

Donor cardiomyocytes exchanged with 42D/44D, 23D/24D and Wt troponin complex (4–5 myocytes per complex). Myofilament force was measured at sarcomere lengths of 1.8 and 2.2 μm at different Ca²⁺-concentrations. Ca²⁺-sensitivity derived from the midpoint of the force–pCa relationship (pCa₅₀) increased at 2.2 μm compared to 1.8 μm for all complexes, however, the difference was only significant in 23D/24D. Stretching of cardiomyocytes from 1.8 to 2.2 μm increased maximal (F_max) and passive force (F_pas) in all groups. There was no significant effect of sarcomere length on nHill (steepness of the force-pCa curves). Compared to Wt, 42D/44D and 23D/24D significantly decreased Ca²⁺-sensitivity at both sarcomere lengths (^#P<0.05). No significant differences between the 3 cTn complexes for F_max, F_pas and nHill were found. When two-way ANOVA revealed a significant effect for sarcomere length (P<0.05), paired t-tests were performed to compare cell measurements at two different sarcomere lengths in each cTn-exchange group (*P<0.05, 1.8 vs 2.2 μm). Wt and 23D/24D data have been published before.²³ Values are means ± SEM.

Without	PKA	Wt	42D/44D	23D/24D
Fmax (kN.m−2)	1.8 μm	12.4±0.5	10.3±1.9	11.7±1.1
	2.2 μm	16.2±0.5*	16.3±0.8*	16.3±0.9*
Fpas (kN.m−2)	1.8 μm	2.2±0.3	2.1±0.5	2.9±0.3
	2.2 μm	3.9±0.6*	3.0±0.7*	4.0±0.3*
pCa50	1.8 μm	5.55±0.05	5.26±0.01#	5.37±0.01#
	2.2 μm	5.57±0.05	5.28±0.01#	5.46±0.01*,#
nHill	1.8 μm	1.9±0.1	2.0±0.2	2.0±0.1
	2.2 μm	1.9±0.1	2.1±0.3	1.7±0.1