The outer hair cell (OHC) is believed to play an important role for the normal function of the cochlea, and the cochlear amplification is believed to be based on the OHC electromotility. Recently, various studies such as the measurements of the electromotility and mechanical properties of the OHC and the estimation of the force production of the cell using OHC models have been done to clarify the mechanism of the cochlear amplification. In these reports, although the elastic properties of the cell have been well analyzed, the longitudinal viscoelastic properties of the cell, which may affect the basilar membrane vibration, have not been characterized yet.
Therefore, in this study, first, the cell was held at cuticular plate by an elastic probe and at a basal part of the lateral wall by a glass pipette, and the cell was stretched to the longitudinal direction and the force generated in the cell was measured. Then, by adapting a three parameter Voigt model, which includes a spring with stiffness k
1 in series with a Voigt element containing a spring with stiffness k
2 and a dashpot characterized by η, to the measurement results, an attempt was made to evaluate the viscoelastic properties of the OHC. The results are as follows:
1. When the OHC is stretched by the glass pipette, a large force is generated instantaneously and then gradually relaxed.
2. Analyzing the measurement results using the three parameter Voigt model, the stiffness parameters of the OHC k
1, k
2 and the viscous parameter η in the model are (0. 98±0. 68)×10
-3 N/m, (1.0±1.0)×10
-3 N/m and (17±13)×10
-3 N·s/m, respectively. Based on this model, adaptation and relaxation characteristics of the OHC are estimated, and the adaptation and relaxation times are obtained to be 24sec and 9. 1sec, respectively.
3. It can be said that OHCs show much stronger viscoelastic behavior than erythrocytes and leukocytes.
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