Otoacoustic emissions, hair cells, and myosin motors

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Abstract
The stereovillar bundles of hair cells show active movements that may be generated by the putative myosin-actin interactions underlying hair-cell adaptation. Such movement is a possible candidate for the generation of spontaneous otoacoustic emissions (SOAE) in the ear canal of nonmammals. In the basilar papilla of certain lizard families, most hair cells are not coupled by a tectorial membrane, making it easier to assign the energy in emission peaks to defined groups of hair cells. We have studied 62 SOAE in the Bahamian Anole Anolis sagrei, which has about 140 hair cells with "free-standing" bundles in the high-frequency area of its papilla. Individual SOAE peaks were traced to between 3 and 38 hair cells, and the mean power output per hair cell was calculated to be 141 aW. The number of bundle myosins putatively involved in the generation of each SOAE was estimated and the force generated by each myosin at 1 kHz calculated to be approximately 0.1 pN. The data support the idea that hair cells generate emissions and suggest that myosin produces sufficient power to be the emission motor.