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Cai W, Grosh K. Rate Dependent Cochlear Outer Hair Cell Force Generation: Models and Parameter Estimation. BIORXIV : THE PREPRINT SERVER FOR BIOLOGY 2023:2023.12.13.571371. [PMID: 38168239 PMCID: PMC10760109 DOI: 10.1101/2023.12.13.571371] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/05/2024]
Abstract
The outer hair cells (OHCs) of the mammalian cochlea are the mediators of an active, nonlinear electromechanical process necessary for sensitive, frequency specific hearing. The membrane protein prestin conveys to the OHC a piezoelectric-like behavior hypothesized to actuate a high frequency, cycle-by-cycle conversion of electrical to mechanical energy to boost cochlear responses to low-level sound. This hypothesis has been debated for decades, and we address two key remaining issues: the influence of the rate dependence of conformal changes in prestin and the OHC transmembrane impedance. We develop a theoretical electromechanical model of the OHC that explicitly includes rate dependence of conformal transitions, viscoelasticity, and piezoelectricity. Using this theory, we show the influence of rate dependence and viscoelasticity on electromechanical force generation. Further, we stress the importance of using the correct mechanical boundary conditions when estimating the transmembrane capacitance. Finally, a set of experiments is described to uniquely estimate the constitutive properties of the OHC from whole-cell measurements.
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Tarnovsky YC, Taiber S, Nissan Y, Boonman A, Assaf Y, Wilkinson GS, Avraham KB, Yovel Y. Bats experience age-related hearing loss (presbycusis). Life Sci Alliance 2023; 6:e202201847. [PMID: 36997281 PMCID: PMC10067528 DOI: 10.26508/lsa.202201847] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/22/2022] [Revised: 03/14/2023] [Accepted: 03/15/2023] [Indexed: 04/01/2023] Open
Abstract
Hearing loss is a hallmark of aging, typically initially affecting the higher frequencies. In echolocating bats, the ability to discern high frequencies is essential. However, nothing is known about age-related hearing loss in bats, and they are often assumed to be immune to it. We tested the hearing of 47 wild Egyptian fruit bats by recording their auditory brainstem response and cochlear microphonics, and we also assessed the cochlear histology in four of these bats. We used the bats' DNA methylation profile to evaluate their age and found that bats exhibit age-related hearing loss, with more prominent deterioration at the higher frequencies. The rate of the deterioration was ∼1 dB per year, comparable to the hearing loss observed in humans. Assessing the noise in the fruit bat roost revealed that these bats are exposed to continuous immense noise-mostly of social vocalizations-supporting the assumption that bats might be partially resistant to loud noise. Thus, in contrast to previous assumptions, our results suggest that bats constitute a model animal for the study of age-related hearing loss.
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Affiliation(s)
- Yifat Chaya Tarnovsky
- School of Neurobiology, Biochemistry, and Biophysics, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
- School of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Shahar Taiber
- School of Neurobiology, Biochemistry, and Biophysics, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
- Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Yomiran Nissan
- School of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Arjan Boonman
- School of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
| | - Yaniv Assaf
- School of Neurobiology, Biochemistry, and Biophysics, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
| | | | - Karen B Avraham
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
- Department of Human Molecular Genetics and Biochemistry, Faculty of Medicine, Tel Aviv University, Tel Aviv, Israel
| | - Yossi Yovel
- School of Zoology, Faculty of Life Sciences, Tel Aviv University, Tel Aviv, Israel
- Sagol School of Neuroscience, Tel Aviv University, Tel Aviv, Israel
- School of Mechanical Engineering, Faculty of Engineering, Tel Aviv University, Tel Aviv, Israel
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Altoè A, Shera CA. The Long Outer-Hair-Cell RC Time Constant: A Feature, Not a Bug, of the Mammalian Cochlea. J Assoc Res Otolaryngol 2023; 24:129-145. [PMID: 36725778 PMCID: PMC10121995 DOI: 10.1007/s10162-022-00884-w] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2022] [Accepted: 12/23/2022] [Indexed: 02/03/2023] Open
Abstract
The cochlea of the mammalian inner ear includes an active, hydromechanical amplifier thought to arise via the piezoelectric action of the outer hair cells (OHCs). A classic problem of cochlear biophysics is that the RC (resistance-capacitance) time constant of the hair-cell membrane appears inconveniently long, producing an effective cut-off frequency much lower than that of most audible sounds. The long RC time constant implies that the OHC receptor potential-and hence its electromotile response-decreases by roughly two orders of magnitude over the frequency range of mammalian hearing, casting doubt on the hypothesized role of cycle-by-cycle OHC-based amplification in mammalian hearing. Here, we review published data and basic physics to show that the "RC problem" has been magnified by viewing it through the wrong lens. Our analysis finds no appreciable mismatch between the expected magnitude of high-frequency electromotility and the sound-evoked displacements of the organ of Corti. Rather than precluding significant OHC-based boosts to auditory sensitivity, the long RC time constant appears beneficial for hearing, reducing the effects of internal noise and distortion while increasing the fidelity of cochlear amplification.
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Affiliation(s)
- Alessandro Altoè
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA, USA.
| | - Christopher A Shera
- Caruso Department of Otolaryngology, University of Southern California, Los Angeles, CA, USA.
- Department of Physics & Astronomy, University of Southern California, Los Angeles, CA, USA.
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