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Voltage- and Tension-Dependent Lipid Mobility in the Outer Hair Cell Plasma Membrane
Hearing requires a series of events. The ear converts sound waves into electrical signals and sends nerve impulses to the brain. There they are interpreted as sound. Sound waves enter through the outer ear and reach the middle ear, where they cause the eardrum to vibrate. The vibrations move through fluid in the hearing part of the inner ear (cochlea) that contain the hair cells. The cochlear outer hair cell (OHC) is fundamental to hearing sensitivity and selectivity of all mammals due to its unique electromotile property that amplifies the cochlear traveling wave, but its mechanism has been unknown. The lateral wall plasma membrane of the cochlea outer hair cell is involved in voltage-dependent changes in cell length, or electromotilty. In order to determine the effects of voltage and tension on lipid mobility, scientists at the Department of Otolaryngology and Communicative Sciences at Baylor College of Medicine, studied the plasma membrane of guinea pig outer hair cells. The outer hair cells were isolated in vitro, stained with a fluorescent membrane lipid and three different manipulations were applied to the cells.
The data suggest the change in membrane fluidity is linked to electromotility. Tension and electromotility are related since tension applied to the OHC influences the voltage dependence of electromotility. Changes in membrane tension induced by the different experimental manipulations in this study, are likely to be responsible for the dynamic changes in membrane fluidity. The data indicate that outer hair cell membrane tension can be modulated by voltage, osmotic challenge, and certain drugs. These tension changes then affect the molecular environment of the membrane, changing its fluidity. A model of passive nanoscale changes in membrane curvatures is suggested. For more information, see the January 28 issue of Science, page 658-662, vol 287; N5453.