FIGURE 3.

Steady-state data from a representative trabecula superfused with Tyrode solution and isoproterenol. Figure caption is the same as that in Figure 2. In panel (A), the isometric end-systolic stress-length relation (upper thick line) and the isometric passive stress-length relation (lower thick line) have been fitted to the six isometric contractions (gray lines) at end-systole (black circles) and at end-diastole (open circles), respectively. These two relations have been transcribed to panels (B–E). The work-loop end-systolic stress-length relation, obtained by fitting to the end-systolic points (filled circles), is dependent on the initial length (lines: blue, green, and magenta, respectively): at L_o (B), 0.95 L_o (C), and 0.90 L_o (D). In panel (E), all stress-length relations are superimposed, where the shaded area indicates the zone of the end-systolic points as interpolated using the self-normalized work-loop stress-length relations in the inset, in which L_init refers to the three initial muscle lengths (L_o, 0.95 L_o, and 0.90 L_o). In panel (F), the shaded area indicates the zone of the heat-stress relations obtained from the three preloaded work-loop contractions and the isometric contractions. The inset shows the three relations between work-loop heat (Q) and stress (S) normalized to their isometric values (subscripted as “isom”).