Laboratoire Physico-Chimie Curie, Centre National de la Recherche Scientifique, Institut Curie, Université Pierre et Marie Curie, 75005 Paris, France.
Proc Natl Acad Sci U S A. 2010 May 4;107(18):8079-84. doi: 10.1073/pnas.0913657107. Epub 2010 Apr 19.
The vertebrate ear benefits from nonlinear mechanical amplification to operate over a vast range of sound intensities. The amplificatory process is thought to emerge from active force production by sensory hair cells. The mechano-sensory hair bundle that protrudes from the apical surface of each hair cell can oscillate spontaneously and function as a frequency-selective, nonlinear amplifier. Intrinsic fluctuations, however, jostle the response of a single hair bundle to weak stimuli and seriously limit amplification. Most hair bundles are mechanically coupled by overlying gelatinous structures. Here, we assayed the effects of mechanical coupling on the hair-bundle amplifier by combining dynamic force clamp of a hair bundle from the bullfrog's saccule with real-time stochastic simulations of hair-bundle mechanics. This setup couples the hair bundle to two virtual hair bundles, called cyber clones, and mimics a situation in which the hair bundle is elastically linked to two neighbors with similar characteristics. We found that coupling increased the coherence of spontaneous hair-bundle oscillations. By effectively reducing noise, the synergic interplay between the hair bundle and its cyber clones also enhanced amplification of sinusoidal stimuli. All observed effects of coupling were in quantitative agreement with simulations. We argue that the auditory amplifier relies on hair-bundle cooperation to overcome intrinsic noise limitations and achieve high sensitivity and sharp frequency selectivity.
脊椎动物的耳朵得益于非线性机械放大作用，从而能够在非常大的声音强度范围内工作。人们认为，这种放大过程源于感觉毛细胞产生的主动力。从每个毛细胞的顶表面突出的机械感觉毛束可以自发地振荡，并作为频率选择性、非线性放大器发挥作用。然而，固有波动会扰乱单个毛束对弱刺激的反应，并严重限制放大作用。大多数毛束通过覆盖的凝胶状结构机械耦合。在这里，我们通过将牛蛙囊泡的毛束的动态力钳与毛束力学的实时随机模拟相结合，检测了机械耦合对毛束放大器的影响。该设置将毛束与两个称为“网络克隆”的虚拟毛束耦合，并模拟了毛束与具有相似特征的两个相邻毛束弹性连接的情况。我们发现，耦合增加了自发毛束振荡的相干性。通过有效地降低噪声，毛束与其网络克隆之间的协同相互作用还增强了正弦波刺激的放大。耦合的所有观察到的效应都与模拟结果定量一致。我们认为，听觉放大器依赖于毛束之间的合作，以克服固有噪声限制，实现高灵敏度和尖锐的频率选择性。
