Fig. 6. Ca²⁺-dependence of steady-state isometric tension, kinetics of tension redevelopment (k_TR) and sinusoidal stiffness (SS) in knock-in Tnnc1^WT/C84Y CMPs. (a) Relative steady-state isometric force as a function of pCa. Force values were normalized to the maximum force generated by each individual CMP. (b) Normalized steady-state isometric force as a function of pCa. The C84Y force values (blue) were normalized to average maximum force produced by WT (red). (c) Ca²⁺-dependence of k_TR. Dashed lines were drawn by eye. (d) k_TR as a function of normalized steady-state isometric force. The force values were normalized to the maximum steady-state isometric force generated by WT. Both solid and dashed lines represent solutions obtained from a 3-state model describing force-k_TR relationships: solid lines represent the best fit parameters (f, g, k_OFF) and k_ON⁶³ and dotted lines represent solutions when all four parameters were either increased by 1 or 3% (upper lines) or decreased by 1 or 3% (lower lines). (e) Ca²⁺-dependence of sinusoidal stiffness. (f) Sinusoidal stiffness as a function of normalized steady-state isometric force. Force values were normalized to the maximum steady-state isometric force generated by WT. Dashed lines were drawn by eye. Data are shown as mean ± S.E.M. (n = 5–6). Best fit parameter estimates from non-linear least square regression on the Hill equation (panels a, b and e) and the 3-state model for force-k_TR relationships (panel d) are summarized in ESI Tables 2 and 3,† respectively.