FORCE GENERATION IN THE OUTER HAIR CELL OF THE COCHLEA

The outer hair cell of the mammalian cochlea has a unique motility dir ectly dependent on the membrane potential, Examination of the force ge nerated by the cell is an important step in clarifying the detailed me chanism as well as the biological importance of this motility. We perf ormed a series of experiments to measure force in which an elastic pro be was attached to the eel near the cuticular plate and the cell was d riven with voltage pulses delivered from a patch pipette under whole-c ell voltage clamp. The axial stiffness was also determined with the sa me cell by stretching it with the patch pipette. The isometric force g enerated by the cell is around 0.1 nN/mV, somewhat smaller than 0.15 n N/mV, predicted by an area motor model based on mechanical isotropy, b ut larger than in earlier reports in which the membrane potential was not controlled. The axial stiffness obtained, however, was, on average , 510 nN per unit strain, about half of the value expected from the me chanical isotropy si the membrane. We extended the area motor theory i ncorporating mechanical orthotropy to accommodate the axial stiffness determined, The force expected from the orthotropic model Mras within experimental uncertainties.