FIGURE 5.

Reduced Ca²⁺ sensitivity in myofibrils isolated from CIA hearts. (A) The submaximal Ca²⁺ activated force was lower in isolated myofibrils from CIA hearts than in controls, whereas maximal Ca²⁺ activated force was not different between the groups. (B) The [Ca²⁺] needed to achieve 50% of maximal myofibrillar force (Ca₅₀) was significantly increased in the CIA group, showing that myofibrillar Ca²⁺ sensitivity was lower in the CIA hearts. (C,D) The rates of force development at the onset of maximum contractions (K_Act) and redevelopment after a shortening step (K_Tr) were both reduced in CIA than in control myofibrils. (E) The rate of relaxation following deactivation (K_Rel) did not differ between CIA and control myofibrils. Average data in (A–E) is displayed as box and whiskers min and max including all points., n = 9. *p < 0.05, †p < 0.01, ‡p < 0.001, repeated measurements anova (A), t test (B–E).