Mechanics of the Cochlear Outer Hair Cell

哺乳动物的正常听力需要外毛细胞(OHC)。它们通过将电能转化为机械能的能力放大内耳的声音振动。干扰力产生机制会导致听力损失。产生这种力的机制尚不清楚，但它存在于OHC的侧壁。侧壁是一种优雅的三层复合纳米结构，在OHC中的结构与力生产一样引人注目。这一提议的长期目标是了解侧壁的纳米级机械解剖促进OHC电-机械力产生的机制，特别是在声频。实验和理论方法将确定侧壁的组织如何沿OHC的轴向引导机械力并补偿粘性阻尼。我们将研究两种可能的分子机制的特征，一种是由马达蛋白质的面内构象变化驱动的，另一种是由面外弯曲电弯驱动的。将使用现代电生理和先进的光学技术。具体目标1将检验侧壁的弹性性质随膜电位变化的假设。在不同的握持电位下，在微管吸入和渗透攻击的条件下，用光钳测量局部细胞壁应变。具体目标2将利用偏振消逝光建立质膜的平面外弯曲的幅度，以响应OHC的主动和被动长度变化。具体目标3是确定侧壁细胞骨架在维持细胞形状和传递主动力量中的作用。细胞在细胞骨架受损和恢复期间的电动反应将允许确定其主动力传递。具体目标4将产生一个完整的OHC有源力产生的纳米级模型。它将包括对三椎板侧壁机械解剖的完整动态描述。该模型将使我们能够预测OHC在声频下的力-变形关系，它将满足OHC力产生机制的所有标准。

Outer hair cells (OHC) are required for normal mammalian hearing. They amplify sound vibrations in the inner ear through their ability to convert electrical to mechanical energy. Interfering with the force generating mechanism results in hearing loss. The mechanism responsible for this force production is unknown but it resides in the OHC's lateral wall. The lateral wall is an elegant, three layered, composite nanostructure that is as structurally conspicuous in the OHC as the force production. The long-term goal of this proposal is to understand the mechanism by which the nanoscale mechanical anatomy of the lateral wall facilitates OHC electomechanical force production, particularly at acoustic frequencies. Experimental and theoretical approaches will determine how the organization of lateral wall directs mechanical force along the OHC's axis and compensates for viscous damping. We will investigate the characteristics of two plausible molecular mechanisms, one driven by in-plane conformational changes of a motor protein and the other by out-of-plane flexoelectric bending. Contemporary electrophysiological and advanced optical techniques will be used. Specific Aim 1 will test the hypothesis that the elastic properties of the lateral wall vary with membrane potential. Local cell wall strains will be measured with optical tweezers and under conditions of micropipet aspiration and osmotic challenge at different holding potentials. Specific aim 2 will establish the magnitude of out-of-plane bending of the plasma membrane in response to active and passive length changes of the OHC using polarized evanescent illumination. Specific aim 3 is to establish the role of the lateral wall cytoskeleton in maintaining cell shape and transmitting active forces. The cell's electromotile response during damage and recovery of the cytoskeleton will allow a determination of its active force transmission. Specific aim 4 will result in a complete nanoscale model of OHC active force production. It will include full dynamic description of the trilaminar lateral wall mechanical anatomy. The model will allow us to predict force-deformation relationships for the OHC at acoustic frequencies and it will meet all the criteria for the mechanism of OHC force production.