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Proceedings of the National Academy of Sciences of the United States of America logoLink to Proceedings of the National Academy of Sciences of the United States of America
. 1989 Jul;86(14):5371–5375. doi: 10.1073/pnas.86.14.5371

Mechanical properties of sensory hair bundles are reflected in their Brownian motion measured with a laser differential interferometer.

W Denk 1, W W Webb 1, A J Hudspeth 1
PMCID: PMC297624  PMID: 2787510

Abstract

By optically probing with a focused, low-power laser beam, we measured the spontaneous deflection fluctuations of the sensory hair bundles on frog saccular hair cells with a sensitivity of about 1 pm/square root of Hz. The preparation was illuminated by two orthogonally polarized laser beams separated by only about 0.2 microns at their foci in the structure under investigation. Slight movement of the object from one beam toward the other caused a change of the phase difference between the transmitted beams and an intensity modulation at the detector where the beams interfered. Maintenance of the health of the cells and function of the transduction mechanism were occasionally confirmed by measuring the intracellular resting potential and the sensitivity of transduction. The root-mean-square (rms) displacement of approximately 3.5 nm at a hair bundle's tip suggests a stiffness of about 350 microN/m, in agreement with measurements made with a probe attached to a bundle's tip. The spectra resemble those of overdamped harmonic oscillators with roll-off frequencies between 200 and 800 Hz. Because the roll-off frequencies depended strongly on the viscosity of the bathing medium, we conclude that hair-bundle motion is mainly damped by the surrounding fluid.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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