Outer Hair Cells
There are two types of hair cells in the mammalian cochlea: the inner hair cells, IHCs and outer hair cells, OHCs. Both are polarized cells with their transduction apparatus at the apical membrane and the synapse at the basal pole connected to each other by a cylindrical (OHC) and pear-shaped (IHC) body. The stereociliary bundle at the apical membrane is responsible for converting the mechanical energy of sound into electrical energy; stereocillia bend in response to sound causing a series of K and Ca channels to open at their base. This electrical signal is then transmitted along the length of the cell. For IHCs it results in Ca-evoked exocytotic release of neurotransmitter at the auditory fiber-hair cell synapse, thus IHCs main function is to relay the temporal information of sound to the auditory fiber and henceforth to brain. For OHCs the change in receptor potential triggers activity in the lateral membrane of the OHC, specifically, changes in the transmembrane potential cause polarization (displacement) currents in the membrane that are accompanied by changes in the length and diameter of the cell. This electromechanical motor works at frequencies up to 50 kHz and requires a membrane protein prestin located in the OHC lateral membrane and intracellular anions. It is essential for amplification of sound at high frequencies. Our objective is to characterize the electrical properties of OHCs to reveal how sound is amplified across the cochlea.
Farinelli F, Brownell WE, Farrell B. Measurement of the specific membrane capacitance of the OHC lateral wall by chemical amputation. In preparation.
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Rabbitt RD, Clifford S, Breneman DK, Farrell B, Brownell WE. Power efficiency of outer hair cell somatic electromotility. PLoS Comput Biol 2009;5:e1000444.
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