ASA 127th Meeting M.I.T. 1994 June 6-10

2aPP6. Variability of voltage dependency of the outer hair cell (OHC) motility voltage sensor.

Sections of Otolaryngol. and Neurobiol., Yale Med. School, 333 Cedar St., New Haven, CT 06510

The OHC is a motile cell in the organ of Corti that functions to mechanically modulate inner hair cell responses. OHC length is voltage dependent; its magnitude varies as a sigmoidal function of voltage. The voltage sensing elements of the mechanical effectors have been evaluated by means of the nonlinear capacitance presented by the sensor's charge movement. The nonlinear capacitance is a bell-shaped function of voltage. The voltage sensitivities of mechanical response and nonlinear capacitance correspond, with the peak capacitance occurring at voltages where the mechanical response is maximal. This voltage (V[sub h]) lies between -40 and -20 mV, on average. The variability of this value within single cells has been studied using a peak capacitance tracking method. It was found that in addition to variability among cells, with V[sub h] ranging from 0 to -80 mV, individual cells also demonstrate variability over time, sometimes hovering within a range of 20 to 30 mV. In some cases, preferred voltage levels are held for several seconds to minutes, thereafter moving to new voltage levels. Since the sensitivity of OHC motility should follow that of the voltage sensor, these results indicate that the motility function may be non-static. [Work supported by NIDCD.]