Figure 4. L48Q cTnC prevents contractile abnormalities in cardiac tissue isolated from hearts containing D230N tropomyosin.

(A) Steady-state T as a percentage of the maximum value (at pCa 4.0) of demembranated cardiac muscle measured over a range of extracellular Ca²⁺ concentrations (pCa = –log([Ca²⁺]). The data are fit with the Hill equation (see Methods section) shown by the solid lines. (B) The pCa at half-maximal T (pCa₅₀) of cardiac preparations from D230N hearts is significantly less than all other groups, whereas the pCa₅₀ of preparations from L48Q plus D230N DTG hearts is not different from WT. Error bars represent SD. Black lines above the bars indicate P < 0.05 between groups using a 1-way ANOVA and a Tukey’s post hoc test of significance. (C) Average twitch T-time traces (in % WT T_peak) of intact trabeculae for each genotype (same color scheme as panel A). The WT T-time trace is shown as a dashed green trace against each variant twitch for comparison. (D) The area under the T-time trace (left ordinate) for each genotype and the resulting TI (right ordinate). See Supplemental Table 2 for numerical values. T, tension; cTnC, cardiac troponin C; Ca²⁺, calcium; T_peak, peak twitch tension; DTG, double-transgenic.