Table 4. Force measurements in donor cardiomyocytes after exchange with recombinant troponin and subsequent PKA treatment.

Donor cardiomyocytes exchanged with 42D/44D, 23D/24D and Wt troponin complex with PKA treatment (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) significantly increased at 2.2 μm compared to 1.8 μm for all complexes, however, significantly less in 42D/44D compared with Wt and 23D/24D. Stretching of cardiomyocytes from 1.8 to 2.2 μm increased maximal (F_max) and passive force (F_pas) in all groups, without affecting nHill (steepness of the force-pCa curves). Compared to Wt, 42D/44D decreased Ca²⁺-sensitivity, reaching significance at sarcomere length 2.2 μm (^#P<0.05). pCa₅₀ of Wt did not significantly differ from 23D/24D after PKA treatment. 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.

With	PKA	Wt	42D/44D	23D/24D
Fmax (kN.m−2)	1.8 μm	12.8±1.1	12.5±1.2	11.1±1.9
	2.2 μm	14.9±1.6*	16.3±0.7*	16.2±2.2*
Fpas (kN.m−2)	1.8 μm	2.0±0.2	2.1±0.2	2.6±0.1
	2.2 μm	2.9±0.2*	3.3±0.5*	3.6±0.3*
pCa50	1.8 μm	5.34±0.06	5.25±0.01	5.37±0.01
	2.2 μm	5.44±0.08*	5.28±0.01*,#	5.48±0.01*
nHill	1.8 μm	2.1±0.1	1.9±0.1	1.7±0.1
	2.2 μm	2.1±0.1	1.9±0.3	1.7±0.2