Fridberger Anders, Tomo Igor, Ulfendahl Mats, Boutet de Monvel Jacques
Center for Hearing and Communication Research, Department of Clinical Neuroscience, Karolinska Institutet, M1 Karolinska Universitetssjukhuset, SE-171 76 Stockholm, Sweden.
Proc Natl Acad Sci U S A. 2006 Feb 7;103(6):1918-23. doi: 10.1073/pnas.0507231103. Epub 2006 Jan 30.
The cochlea contains two types of sensory cells, the inner and outer hair cells. Sound-evoked deflection of outer hair cell stereocilia leads to fast force production that will enhance auditory sensitivity up to 1,000-fold. In contrast, inner hair cells are thought to have a purely receptive function. Deflection of their stereocilia produces receptor potentials, transmitter release, and action potentials in the auditory nerve. Here, we describe a method for rapid confocal imaging. The method was used to image stereocilia during simultaneous sound stimulation in an in vitro preparation of the guinea pig cochlea. We show that inner hair cell stereocilia move because they interact with the fluid surrounding the hair bundles, but stereocilia deflection occurs at a different phase of the stimulus than is generally expected. In outer hair cells, stereocilia deflections were approximately 1/3 of the reticular lamina displacement. Smaller deflections were found in inner hair cells. The ratio between stereocilia deflection and reticular lamina displacement is important for auditory function, because it determines the stimulus applied to transduction channels. The low ratio measured here suggests that amplification of hair-bundle movements may be necessary in vivo to preserve transduction fidelity at low stimulus levels. In the case of the inner hair cells, this finding would represent a departure from traditional views on their function.
耳蜗包含两种感觉细胞，即内毛细胞和外毛细胞。外毛细胞静纤毛的声音诱发偏转导致快速的力产生，这将使听觉灵敏度提高多达1000倍。相比之下，内毛细胞被认为具有纯粹的感受功能。它们静纤毛的偏转在听神经中产生感受器电位、递质释放和动作电位。在这里，我们描述了一种快速共聚焦成像方法。该方法用于在豚鼠耳蜗的体外制备中同时进行声音刺激时对内毛细胞静纤毛进行成像。我们发现内毛细胞静纤毛会移动，因为它们与毛束周围的液体相互作用，但静纤毛的偏转发生在刺激的一个与通常预期不同的相位。在外毛细胞中，静纤毛的偏转约为网状板位移的1/3。在内毛细胞中发现的偏转较小。静纤毛偏转与网状板位移之间的比率对听觉功能很重要，因为它决定了施加到转导通道的刺激。此处测得的低比率表明，在体内可能需要放大毛束运动，以在低刺激水平下保持转导保真度。就内毛细胞而言，这一发现将代表对其功能的传统观点的背离。
