Sound perception via mechano-sensation is a remarkably sensitive and fast transmission process, converting sound as a mechanical input to neural signals in a living organism. Although knowledge of auditory hair cell functions has advanced over the past decades, challenges remain in understanding their biomechanics, partly because of their biophysical complexity and the lack of appropriate probing tools. Most current studies of hair cells have been conducted in a relatively low-frequency range (<1000 Hz); therefore, fast kinetic study of hair cells has been difficult, even though mammalians have sound perception of 20 kHz or higher. Here, we demonstrate that the magnetic force nanoprobe (MFN) has superb spatiotemporal capabilities to mechanically stimulate spatially-targeted individual hair cells with a temporal resolution of up to 9 μs, which is equivalent to approximately 50 kHz; therefore, it is possible to investigate avian hair cell biomechanics at different tonotopic regions of the cochlea covering a full hearing frequency range of 50 to 5000 Hz. We found that the variation of the stimulation frequency and amplitude of hair bundles creates distinct mechanical responsive features along the tonotopic axis, where the kinetics of the hair bundle recovery motion exhibits unique frequency-dependent characteristics: basal, middle, and apical hair bundles can effectively respond at their respective ranges of frequency. We revealed that such recovery kinetics possesses two different time constants that are closely related to the passive and active motilities of hair cells. The use of MFN is critical for the kinetics study of free-standing hair cells in a spatiotemporally distinct tonotopic organization.
Bibliographical noteFunding Information:
for helpful discussions, Seung-hyun Noh for providing magnetic nanoparticles, and Dr. Sebastiaan Meenderink and Alert Kao for providing the analysis software. J.C. acknowledges support from the Institute for Basic Science (IBS-R026-D1), the U.S. Air Force Office of Scientific Research (FA9550-12-1-0407), and the Korea Healthcare Technology R&D Project (HI08C2149). J.B. acknowledges supports from the National Research Foundation of Korea (2014R1A2A1A11051024 and 2014M3A9D5073865), and the Yonsei University Futureleading Research Initiative (2015-22-0058).
© 2016 American Chemical Society.
All Science Journal Classification (ASJC) codes
- Materials Science(all)
- Condensed Matter Physics
- Mechanical Engineering