Fig. 3.

Facilitation of hair bundle recovery in the bullfrog’s sacculus by mechanical displacement. (A) In a displacement-clamp experiment, a feedback system imposed a ramp displacement on a hair bundle (first trace), moving the bundle first in the positive direction to prevent prompt recovery, and then more extensively in the negative direction. At three times during this paradigm, a 500-ms epoch of ±25-nm, 40-Hz sinusoidal stimulation was superimposed on the displacement-command signal. An iontophoretic pulse (third trace) released EDTA to break tip links. The force (second trace) necessary to clamp the bundle at the outset (Initial) diminished after exposure to iontophoretically applied EDTA (Exposure) but recovered almost completely by the experiment’s end (Recovered). The variance of the force (fourth trace) confirmed the bundle’s softening after iontophoresis and its recovery during the negative phase of the ramp. The dashed line represents the background noise. (B) Enlarged records of the hair bundle displacement (top traces) and clamp force (bottom traces) from A demonstrate that maintaining an oscillation of similar—or even greater—magnitude required less force shortly after iontophoresis. (C) Data from seven hair cells, which are numbered as in Table 1, reveal a significant decrease (P < 0.01 by a single-sided paired t test) in hair bundle stiffness after iontophoretic pulses. The stiffness then recovered significantly (P < 0.05 by the same test) following negative hair bundle displacements. The bundle whose responses are depicted in A and B is number 4; SDs are shown when they exceed the size of the data points.