Motility voltage sensor of the outer hair cell resides within the lateral plasma membrane

The outer hair cell (OHC) from the organ of Corti is believed to be responsible for the mammal's exquisite sense of hearing. A membrane-based motile response of this cell underlies the initial processing of acoustic energy. The voltage-dependent capacitance of the OHC, possibly reflecting charge movement of the motility voltage sensor, was measured in cells during intracellular dialysis of trypsin under whole cell voltage clamp. Within 10 min after dialysis, light and electron microscopic examination revealed that the subplasmalemmal structures, including the cytoskeletal framework and subsurface cisternae, were disrupted and/or detached from adjacent plasma membrane. Dialysis of heat-inactivated trypsin produced no changes in cell structure. Simultaneous measures of linear and nonlinear membrane capacitance revealed minimal changes, indicating that contributions by subsurface structures to the generation of the nonlinear capacitance are unlikely. This study strongly suggests that voltage-dependent charge movement in the OHC reflects properties of the force generator's voltage sensor and that the sensor/motor resides solely within the lateral plasma membrane.