Fig. 3.

Native thin filament motility at pCa 5 over native thick filaments from SOL and EDL muscles. (A) Illustration of native thin filament trajectories observed over native thick filaments, which, as in B, are described as either a trajectory with a constant velocity (i.e., single phase; gray arrow) or having dual phases, where there is an initial fast velocity phase (light blue arrow) in the D-zone that is followed by a slower velocity phase (light green arrow) that corresponds to the length of the C-zone. (B) Representative EDL thin filament displacement vs. time trajectories, illustrating the behavior of dual-phase trajectories. The initial fast velocity phase (blue) persists for ∼350 to 400 nm, approximately the length of the D-zone, followed by a slow velocity phase that corresponds to the expected length of the C-zone (∼400 nm, green). (C) Percentage of observed thin filament trajectories that have single versus dual velocity phases. (D) The velocities that are associated with single phase and each of the dual velocity phase trajectories for the SOL and EDL thick filaments. The single-phase velocities of both SOL and EDL thin filaments are comparable to the fast velocity phase for the dual-phase trajectories. All data are presented as mean ± SEM. Data are summarized in Table 3.