Biology subjects

Iwasa, K. H.

Publications and source records attributed to Iwasa, K. H..

2 recordsLinked to original sources

bioRxiv2025

Effectiveness of Outer Hair Cells as Cochlear Amplifier: Coupled Oscillator Models

Outer hair cells (OHCs) are essential for the sensitivity and frequency specificity of the mammalian ear. To perform this function, OHCs need to amplify the motion of the basilar membrane, which is much stiffer than themselves. OHCs must overcome this impedance mismatch for their amplifying function particularly at high frequencies, where the mismatch is largest. This issue could be solved by the existence of multiple modes of motion. Here, systems of two coupled oscillators are examined as the simplest of such cases. It is found that some of these model systems indeed make OHCs function as an effective amplifier by overcoming the impedance mismatch. This result suggests that the elaborate structure of the organ of Corti, which can support multiple modes of motion, is a key to the high frequency performance of the mammalian ear. SignificanceThe mammalian ear depends on outer hair cells, which work as the cochlear amplifier. The mechanism, with which outer hair cells perform this biological function, is of great interest. The present paper addresses a question, how soft outer hair cells can amplify the vibration of the much stiffer basilar membrane. It shows that the elaborate structure of the cochlea, which supports multiple modes of motion, must be a key to the exquisite performance of the mammalian ear. It also shows that the properties of outer hair cells obtained from isolated cell preparations are compatible with their physiological function.

biophysics↗

bioRxiv2020

Kinetic Membrane Model of Outer Hair Cells

The effectiveness of outer hair cells (OHCs) in amplifying the motion of the organ of Corti, and thereby contributing to the sensitivity of mammalian hearing, depends on the mechanical power output of these cells. Electromechanical coupling in OHCs, which enables these cells to convert electrical energy into mechanical energy, has been analyzed in detail using isolated cells using primarily static membrane models. In the preceding reports, mechanical output of OHC was evaluated by developing a kinetic theory based on a simplified onedimensional (1D) model for OHCs. Here such a kinetic description of OHCs is extended by using the membrane model, which has been used for analyzing in vitro experiments. The present theory predicts, for systems without inertial load, that elastic load enhances positive shift of voltage dependence of the membrane capacitance due to turgor pressure. For systems with inertia, mechanical power output also depends on turgor pressure. The maximal power output is, however, similar to the previous prediction of up to [~]10 fW based on the 1D model. Statement of SignificanceThis paper is an attempt for developing a physical model to clarify the mechanism of outer hair cells in performing their role as an amplifier in mammalian hearing. Specifically, this paper extends a static model of these cells into a dynamic one to evaluate mechanical power production, which is essential for the function of these cells. It clarifies the assumptions essential for a previous phenomenological theory, a 1-D model. In addition, it describes the effect of turgor pressure on mechanical power generation.

biophysics↗