Cellular and molecular mechanisms of mechanical amplification in the mammalian cochlea

Abstract

The mammalian cochlea is an amazing evolutionary achievement. The active mechanism housed in the cochlea, the cochlear amplifier, can amplify weak sound stimuli 100-1,000 times over a wide range of incoming frequencies. It confers remarkable sensitivity and exquisite frequency selectivity to the mammalian auditory system. The inner ear contains two types of sensory cells: inner hair cells, which convert the mechanical signal to an electrical signal, and outer hair cells (OHCs), which amplify the mechanical vibration of the cochlea's basilar membrane. OHCs can elongate and contract in response to an oscillation of membrane potential at frequencies of at least 70 kHz. This salient feature of OHCs, termed electromotility, forms the cellular basis of the sound amplification process. Electromotility originates in the motor protein particles embedded in the lateral plasma membrane of the OHCs. The motor protein-prestin-has been cloned. Several different molecular models of the hair cell motor complex have been proposed based on recent studies. This review aims to provide an update on the cellular and molecular mechanisms of cochlear amplification. © 2007 Springer Science+Business Media, LLC. All rights reserved.