Howard Hughes Medical Institute and Laboratory of Sensory Neuroscience, The Rockefeller University, 1230 York Avenue, New York, New York 10065, USA.
Nature. 2011 May 22;474(7351):376-9. doi: 10.1038/nature10073.
The detection of sound begins when energy derived from an acoustic stimulus deflects the hair bundles on top of hair cells. As hair bundles move, the viscous friction between stereocilia and the surrounding liquid poses a fundamental physical challenge to the ear's high sensitivity and sharp frequency selectivity. Part of the solution to this problem lies in the active process that uses energy for frequency-selective sound amplification. Here we demonstrate that a complementary part of the solution involves the fluid-structure interaction between the liquid within the hair bundle and the stereocilia. Using force measurement on a dynamically scaled model, finite-element analysis, analytical estimation of hydrodynamic forces, stochastic simulation and high-resolution interferometric measurement of hair bundles, we characterize the origin and magnitude of the forces between individual stereocilia during small hair-bundle deflections. We find that the close apposition of stereocilia effectively immobilizes the liquid between them, which reduces the drag and suppresses the relative squeezing but not the sliding mode of stereociliary motion. The obliquely oriented tip links couple the mechanotransduction channels to this least dissipative coherent mode, whereas the elastic horizontal top connectors that stabilize the structure further reduce the drag. As measured from the distortion products associated with channel gating at physiological stimulation amplitudes of tens of nanometres, the balance of viscous and elastic forces in a hair bundle permits a relative mode of motion between adjacent stereocilia that encompasses only a fraction of a nanometre. A combination of high-resolution experiments and detailed numerical modelling of fluid-structure interactions reveals the physical principles behind the basic structural features of hair bundles and shows quantitatively how these organelles are adapted to the needs of sensitive mechanotransduction.
当源自声刺激的能量使毛细胞顶部的毛束发生偏转时，声音的检测就开始了。随着毛束的移动，纤毛和周围液体之间的粘性摩擦力对耳朵的高灵敏度和尖锐的频率选择性构成了基本的物理挑战。解决这个问题的部分方法在于利用能量进行频率选择性声音放大的主动过程。在这里，我们证明了解决方案的另一部分涉及毛束内液体和纤毛之间的流固相互作用。通过对动态缩放模型进行力测量、有限元分析、流体动力力的分析估计、随机模拟以及对毛束的高分辨率干涉测量，我们描述了在小毛束偏转过程中各个纤毛之间力的起源和大小。我们发现，纤毛的紧密贴合有效地固定了它们之间的液体，从而减少了阻力并抑制了相对挤压但不抑制纤毛运动的滑动模式。倾斜取向的顶端链接将机械转导通道与这种最小耗散相干模式耦合，而进一步稳定结构的弹性水平顶连接器则进一步减少了阻力。从与生理刺激幅度为数十纳米的通道门控相关的失真产物测量，毛束中粘性和弹性力的平衡允许相邻纤毛之间发生仅包含数纳米分数的相对运动模式。高分辨率实验与流体结构相互作用的详细数值建模相结合，揭示了毛束基本结构特征背后的物理原理，并定量显示了这些细胞器如何适应敏感机械转导的需求。
