Fig 3. Mechanical response of an X. laevis rod to light flashes.

The position of a bead sealed against the tip of the rod OS is monitored with OTs (see Methods). Following a bright flash of 491 nm, equivalent to about 10⁴ R*, a transient shrinkage is observed. (A) Bright-field IR image, showing a trapped bead in contact with the tip of the rod OS (scale bar, 10 μm). (B) Detail of the 3D tracking system. (C) Light-induced shifts in the Z axis of the trapped bead (downward is negative). (D) Expansion of the time base in E to examine the delay between light stimulus and bead movement. (E) Bead displacement along the direction of the rod OS (shrinkage is negative, and elongation is positive). (F) Bead displacement in the direction perpendicular to the rod OS axis. Data are representative of mean ± SD of 5 different experiments. IR, infrared; OS, outer segment; OTs, optical tweezers.