Figure 4.
Effect of TnTF88L on γ at short and long SLs. (A and B) Effect of TnTF88L on the force response to a 2% sudden stretch imposed on a representative muscle fiber at short SL (A) and long SL (B). Force data were normalized to the isometric steady-state value before ML perturbation, and length data were normalized to the initial ML. Fss represents the isometric steady-state value before ML perturbation, and Fnss represents the new steady-state force corresponding to an increase in ML. Parameter γ represents the negative impact of strained XBs on the recruitment of other force-bearing XBs and is estimated by fitting the NLRD model to the force response phases to various amplitude ML perturbations (Fig. 1; Ford et al., 2010). When the negative effect of strained XBs on the state of other force-bearing XBs is less pronounced, the magnitude of force decline is lesser; that is, the nadir is less pronounced and γ is attenuated. (C) Bar graph showing the effect of TnTF88L on γ at short and long SLs. Estimates from several muscle fibers per group were averaged and presented as mean ± SEM. Two-way ANOVA revealed a marginally significant TnT–SL interaction effect (P = 0.051) on γ. Post hoc multiple pairwise comparisons (Fisher’s LSD) were used to determine significant differences between groups. Asterisks indicate significant difference from TnTWT at a given SL (*, P < 0.05). The number of fibers measured (from three hearts) for all groups was 10.