Crawford A C, Fettiplace R
J Physiol. 1985 Jul;364:359-79. doi: 10.1113/jphysiol.1985.sp015750.
The mechanical behaviour of the ciliary bundles of hair cells in the turtle cochlea was examined by deflecting them with flexible glass fibres of known compliance during simultaneous intracellular recording of the cell's membrane potential. Bundle motion was monitored through the attached fibre partially occluding a light beam incident on a photodiode array. The change in photocurrent was assumed to be proportional to bundle displacement. For deflexions of 1-100 nm towards the kinocilium, the stiffness of the ciliary bundles was estimated as about 6 X 10(-4) N/m, with the fibre attached to the top of the bundle. When the fibre was placed at different positions up the bundle, the stiffness decreased approximately as the inverse square of the distance from the ciliary base. This suggests that the bundles rotate about an axis close to the apical pole of the cell and have a rotational stiffness of about 2 X 10(-14) N. m/rad. Step displacements of the fixed end of the flexible fibre caused the hair cell's membrane potential to execute damped oscillations; the frequency of the oscillations in different cells ranged from 20 to 320 Hz. Displacements towards the kinocilium always produced membrane depolarization. The amplitude of the initial oscillation increased with displacements up to 100 nm and then saturated. For small displacements of a few nanometres, the hair cell's mechanoelectrical sensitivity was estimated as about 0.2 mV/nm. Force steps delivered by the flexible fibre caused the bundle position to undergo damped oscillations in synchrony with the receptor potential. The mechanical oscillations could be abolished with large depolarizing currents that attenuated the receptor potential. When placed against a bundle, a fibre's spontaneous motion increased and became quasi-sinusoidal with an amplitude several times that expected from the compliance of the system. It is suggested that the hair bundle drives the fibre. We conclude that turtle cochlear hair cells contain an active force generating mechanism.
在对龟类耳蜗毛细胞的细胞膜电位进行细胞内同步记录的过程中，通过用已知柔顺性的柔性玻璃纤维使毛细胞的纤毛束发生偏转，来研究其力学行为。通过附着的纤维部分遮挡入射到光电二极管阵列上的光束来监测纤毛束的运动。假定光电流的变化与纤毛束位移成正比。当纤毛束朝着动纤毛方向发生1 - 100纳米的偏转时，将纤维附着在纤毛束顶部，测得纤毛束的刚度约为6×10⁻⁴牛/米。当纤维置于纤毛束上不同位置时，刚度大约随着离纤毛基部距离的平方反比而减小。这表明纤毛束围绕靠近细胞顶端极的轴旋转，其旋转刚度约为2×10⁻¹⁴牛·米/弧度。柔性纤维固定端的阶跃位移使毛细胞的细胞膜电位产生阻尼振荡；不同细胞中振荡的频率范围为20至320赫兹。朝着动纤毛的位移总是会导致膜去极化。初始振荡的幅度随着位移增加到100纳米然后饱和。对于几纳米的小位移，毛细胞的机械电敏感性估计约为0.2毫伏/纳米。柔性纤维施加的力阶跃使纤毛束位置与感受器电位同步发生阻尼振荡。大的去极化电流可消除机械振荡，该电流会减弱感受器电位。当一根纤维靠在纤毛束上时，其自发运动增加并变为准正弦形式，幅度是系统柔顺性预期值的几倍。有人认为是毛束驱动了纤维。我们得出结论，龟类耳蜗毛细胞含有一种主动产生力的机制。
