MEMBRANES PROPERTIES OF CELLS COMPRISING THE OHC SYSTEM

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The overall aim of this project is to analyze the membrane properties of several isolated cell types from the inner ear using the whole cell voltage clamp technique. The cell types (outer hair cells [OHCs], Type II spiral ganglion cells, and Deiter cells) were chosen because they all functionally relate (directly or indirectly to the OHC system. This system has recently been shown to be very important for normal cochlear function. Several properties of OHCs will be studied, including their inward Ca+2 currents, the mechanism of gadolinium induced block of voltage induced OHC motility, and the frequency response of OHC motility. These evaluations will be made by measuring the voltage dependence of these currents and motility blocking effects, by comparing the motility characteristics to those of stretch receptors, and by measuring OHC mechanical response magnitude induced by AC stimuli. The ionic conductances of Type II spiral ganglion cells and Deiter cells will be analyzed to determine their roles in the OHC system. Specifically, Deiter cells, which are coupled to other supporting cells via gap junctions, will be evaluated via voltage clamp to determine whether they possess mechanisms (e.g., inwardly directed K+ currents) which might aid in the ionic homeostasis of the organ of Corti. Type II spiral ganglion cells will be evaluated in similar fashion to determine whether they possess the ionic conductances necessary for the transfer of acoustic information to the central nervous system. Since no electrophysiological information is available on this cell type, this is an important issue. Understanding these phenomena will shed light upon the role that OHCs play in fine frequency tuning within the organ of Corti via mechanical feedback mechanisms. They will also help elucidate the effects of pathologies of the outer hair cell system, including ionic imbalances (e.g., Meniere's disease), noise induced hearing loss, and tinnitus.