Fig. 4.

Ca²⁺ sensitivity decreased maximally at ∼55% of bisphosphorylated cTnI Ser²³/Ser²⁴ in end-stage failing cardiomyocytes. Shown is the relation between bisphosphorylated cTnI and myofilament Ca²⁺ sensitivity in IDCM cardiomyocytes (4–5 cells) exchanged with different concentrations of recombinant cTn-DD (concentrations of 0.06125, 0.125, 0.25, 0.5, 1.0, and 2.0 mg/ml of cTnI-DD were used). Cardiomyocytes immersed in exchange solution without complex during the overnight exchange served as controls (0% cTn exchange). cTnI-DD exchange caused a gradual decline in pCa₅₀ of 0.13 ± 0.03, saturating at 51 ± 5% of troponin exchange. *P < 0.05, **P < 0.01, and ***P < 0.001, control vs. cTnI-DD (by posttest Bonferroni analyses of one-way ANOVA). Solid line: pCa₅₀ = 5.608 − 0.0028 × exchange percentage(cTnI-DD).