Fig. 4.

Thin filament changes with SL, titin cleavage, and velocity. A6 (A and B), spacings and T3 spacings (C and D) were recorded as explained in Fig. 2. (E) Cartoon summary of the sarcomere at short and long lengths, with proposed A-band bridges added. The ON state is reduced at long lengths after titin cleavage. (F) Sarcomere stretch from short (Top) to long (Bottom) extends the entire I-band titin producing relatively low titin-based forces, but evidence indicates that titin extension can be modified by titin–thin filament interactions around the N2A/PEVK region, functionally shortening the free titin to the stiffer PEVK region, leading to relatively larger titin-based forces after stretch. Higher velocities can be expected to detach the interaction, reducing titin-based forces. *P < 0.05 from pre to post values. ^P < 0.05 between quick stretch and control (pre) data. Also see SI Appendix, Tables S1, S2, S4, S5, S7, and S8.