Rabbitt R D, Ayliffe H E, Christensen D, Pamarthy K, Durney C, Clifford S, Brownell W E
Department of Bioengineering, University of Utah, 506 BPRB 20 South, 2030 East Salt Lake City, UT 84112, USA.
Biophys J. 2005 Mar;88(3):2257-65. doi: 10.1529/biophysj.104.050872. Epub 2004 Dec 21.
Our results demonstrate high-frequency electrical resonances in outer hair cells (OHCs) exhibiting features analogous to classical piezoelectric transducers. The fundamental (first) resonance frequency averaged f(n) approximately 13 kHz (Q approximately 1.7). Higher-order resonances were also observed. To obtain these results, OHCs were positioned in a custom microchamber and subjected to stimulating electric fields along the axis of the cell (1-100 kHz, 4-16 mV/80 microm). Electrodes embedded in the side walls of the microchamber were used in a voltage-divider configuration to estimate the electrical admittance of the top portion of the cell-loaded chamber (containing the electromotile lateral wall) relative to the lower portion (containing the basal plasma membrane). This ratio exhibited resonance-like electrical tuning. Resonance was also detected independently using a secondary 1-MHz radio-frequency interrogation signal applied transversely across the cell diameter. The radio-frequency interrogation revealed changes in the transverse electric impedance modulated by the axial stimulus. Modulation of the transverse electric impedance was particularly pronounced near the resonant frequencies. OHCs used in our study were isolated from the apical region of the guinea pig cochlea, a region that responds exclusively to low-frequency acoustic stimuli. In this sense, electrical resonances we observed in vitro were at least an order of magnitude higher (ultrasonic) than the best physiological frequency of the same OHCs under acoustic stimuli in vivo. These resonance data further support the piezoelectric theory of OHC function, and implicate piezoelectricity in the broad-band electromechanical behavior of OHCs underlying mammalian cochlear function.
我们的研究结果表明，外毛细胞（OHC）中存在高频电共振，其表现出与经典压电换能器类似的特征。基本（第一）共振频率平均约为f(n) 13千赫兹（品质因数Q约为1.7）。还观察到了高阶共振。为获得这些结果，将OHC置于定制的微腔中，并沿细胞轴施加刺激电场（1 - 100千赫兹，4 - 16毫伏/80微米）。嵌入微腔侧壁的电极采用分压器配置，以估计细胞加载腔顶部（包含电动性侧壁）相对于下部（包含基底质膜）的电导率。该比率呈现出类似共振的电调谐。还使用横向施加在细胞直径上的1兆赫兹二次射频询问信号独立检测到了共振。射频询问揭示了由轴向刺激调制的横向电阻抗变化。横向电阻抗的调制在共振频率附近尤为明显。我们研究中使用的OHC是从豚鼠耳蜗的顶端区域分离出来的，该区域仅对低频声刺激作出反应。从这个意义上说，我们在体外观察到的电共振比这些OHC在体内声刺激下的最佳生理频率至少高一个数量级（超声波频率）。这些共振数据进一步支持了OHC功能的压电理论，并表明压电性参与了哺乳动物耳蜗功能基础的OHC宽带机电行为。
