The long-term goal of these studies is to identify the physical basis of outer hair cell electromotility. The outer hair cell enhances the sensitivity and frequency selectivity of mammalian hearing by converting the energy of hair energy. The motor is known to reside in the outer hair cell's lateral wall, a 100 nanometer thick, three-layer structure composed of two membranes with a cytoskeletal network sandwiched between them. The specific objective of this project period is to identify the contributions of the lateral wall to the modulation and maintenance of the electrochemical gradient necessary for cell function, specifically electromotility. Coordinated theoretical and experimental approaches identify how the unique molecular organization of the lateral wall influences the transport of ions, water and other molecules through the narrow space between the membranes. The contribution of cholesterol and other lipids to the lateral wall membranes wil be examined to determine how they affect electromotility and membrane permeability. The relative electromotile movement of the membranes will be measured with the goal of determining the motor location. The effect of genetically removing specific cytoskeletal proteins on electromotility will be measured. Methods include outer hair cell isolation from normal and geneticall altered animals; voltage-clamp with voltage-sensitive dyes and two-pipette recording; measuring the flow of fluorescent markers with confocal microscopy; video microscopy and photometric measures of displacement; and computational modeling. Changes in outer hair cell electromotility will be ascertained in animal models by measuring otoacoustic emissions. New medical treatments for hearing disorders associated with high cholesterol may be suggested if it is found they result from a direct action on the lateral wall. The deafness found in mice with genetically induced deficits of specific cytoskeletal proteins ha implications for the molecular basis of other forms of hereditary sensory-neural hearing loss. Clarification of the physical principles underlying electromotility will also contribute to the emerging field of biological nanotechnology.
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