Figure 1.

SL dependency of maximal tension and E_D in young and adult guinea pig cardiac muscle preparations. Maximal tension was measured by exposing muscle preparations to saturating Ca²⁺ concentrations (pCa 4.3) in a constantly stirred chamber. E_D was estimated as the slope of the linear relationship between F₁–F_ss and the corresponding ML changes (see Fig. S1) and thus provides an approximate measure of the number of strongly bound XBs. (A and B) Bar graphs showing the SL-dependent effect on (A) maximal tension and (B) E_D in young and adult muscle preparations. Two-way ANOVA revealed that the main effect of SL was significant for both maximal tension (P < 0.001) and E_D (P = 0.002). The main effect of MHC was not significant for both maximal tension (P = 0.91) and E_D (P = 0.24). Post hoc multiple comparisons (Holm–Sidak method) were used to determine significant differences between groups. Asterisks and hash marks indicate a significant difference when compared with data within each group (*, P < 0.05 and ***, P < 0.001 for 1.9 vs. 2.3 µm). The number of preparations measured for all groups was 10. Data are expressed as means ± SEM.