AN ELECTRICAL TUNING MECHANISM IN TURTLE COCHLEAR HAIR-CELLS
AN ELECTRICAL TUNING MECHANISM IN TURTLE COCHLEAR HAIR-CELLS
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DOI：
10.1113/jphysiol.1981.sp013634
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发表时间：
1981-01-01
影响因子：
5.5
通讯作者：
FETTIPLACE, R
中科院分区：
文献类型：
--
作者：
CRAWFORD, AC;FETTIPLACE, R
细胞内记录由单个耳蜗毛细胞在分离的海龟的半头。记录细胞在两种情况下的电反应：用不同频率的低强度声音刺激耳朵和通过细胞内电极注入电流步骤。在多大程度上，耳蜗的频率选择性可以由毛细胞的电学特性来解释，进行了评估。在低水平的声刺激下，毛细胞受体电位的振幅与声压成正比。线性调谐曲线被定义为细胞在其线性范围内工作时，细胞的灵敏度作为频率的函数，对特征频率为86-425 Hz的许多毛细胞进行了测量。在小电流条件下，振荡的频率和由振荡衰减得到的电共振的品质因子(Q)接近于由声音呈现得到的毛细胞线性调谐曲线的特征频率和Q。毛细胞的膜电位变化为小电流脉冲或低强度的音调爆发，可以通过将毛细胞表示为由电感、电阻和电容器组成的简单电谐振器来描述。当将29- 250nm的步位移应用于放置在基底乳头毛细胞外的微管时，可以记录到听神经中单个纤维的初始周期性脉冲发射。通过相同的微管注入高达1na的电流，听神经放电没有产生任何变化。电流注入不会产生电极尖端的大体运动。假设电共振独立于其他滤波阶段，通过将线性调谐曲线除以细胞阻抗作为频率的函数来评估电共振对毛细胞调谐的贡献；因此，共振可以解释声学调谐曲线的尖端。残余滤波器表现出高频滚降，转角频率为500- 600hz，在所有细胞中都相似，而低频滚降，转角频率为30 - 350hz，因细胞而异，但与细胞的特征频率无关。在10个细胞中测量了相对于鼓室声压的受体电位的相位。在低强度下，相位特性与声压无关。低频时，感受器电位将声音引导270 ~ 360度，在特征频率区域出现90 ~ 180度的相位滞后；相变的突然性取决于电池的Q值。计算出的电谐振器的相移作为频率的函数，从受体电位的相位特性中减去。减相法去除特征频率附近的急剧相变，在该频率区域，减相后的剩余相位在+ 180度处近似恒定。毛细胞去极化可能是基底膜向前庭阶梯移位的反应。各细胞残相特征的高频区相似。每个毛细胞都有自己的电共振机制，这是受体电位频率选择性的主要原因。细胞显示出宽带通滤波器的证据，其高频部分可能是由中耳的作用产生的。
Intracellular recordings were made from single cochlear hair cells in the isolated half-head of the turtle. The electrical responses of the cells were recorded under 2 conditions: when the ear was stimulated with low-intensity tones of different frequencies and when current steps were injected through the intracellular electrode. The extent to which cochlear''s frequency selectivity could be accounted for by the electrical properties of the hair cells, was evaluated. At low levels of acoustic stimulation, the amplitude of the hair cell receptor potential was proportional to sound pressure. The linear tuning curve, which is defined as the sensitivity of the cell as a function of frequency when the cell is operating in its linear range, was measured for a number of hair cells with characteristic frequencies from 86-425 Hz. For small currents the frequency of the oscillations and the quality factor (Q) of the electrical resonance derived from the decay of the oscillations were close to the characteristic frequency and Q of the hair-cell linear tuning curve obtained from sound presentations. The hair cell''s membrane potential change to small-current pulses or low-intensity tone bursts could be largely described by representing the hair cell as a simple electrical resonator consisting of an inductance, resistor and capacitor. When step displacements of 29-250 nm were applied to a micropipette, placed just outside a hair cell in the basilar papilla, an initial periodic firing of impulses could be recorded from single fibers in the auditory nerve. Currents of up to 1 nA, injected through the same micropipette, failed to produce any change in the auditory nerve discharge. Current injection does not produce gross movements of the electrode tip. The contribution of the electrical resonance to hair-cell tuning was assessed by dividing the linear tuning curve by the cell impedance as a function of frequency, assuming that the electrical resonance is independent of other filtering stages; the resonance can thus account for the tip of the acoustical tuning curve. The residual filter exhibited a high-frequency roll-off with a corner frequency at 500-600 Hz, similar in all cells, and a low-frequency roll-off, with a corner frequency from 30 to 350 Hz which varied from cell to cell but was uncorrelated with the characteristic frequency of the cell. The phase of the receptor potential relative to the sound pressure at the tympanum was measured in 10 cells. For low intensities the phase characteristic was independent of sound pressure. At low frequencies the receptor potential led the sound by 270-360.degree., and in the region of the characteristic frequency there was an abrupt phase lag of 90-180.degree.; the abruptness of the phase change depended upon the Q of the cell. The calculated phase shift of the electrical resonator as a function of frequency was subtracted from the phase characteristic of the receptor potential. The subtraction removed the sharp phase transition around the characteristic frequency, and in this frequency region the residual phase after subtraction was approximately constant at + 180.degree.. Hair cells probably depolarize in response to displacements of the basilar membrane towards the scala vestibuli. The high-frequency region of the residual phase characteristic was similar in all cells. Each hair cell contains its own electrical resonance mechanism which accounts for most of the frequency selectivity of the receptor potential. Cells show evidence of a broad band-pass filter, the high frequency portion of which may be produced by the action of the middle ear.