Somatic stiffness of cochlear outer hair cells is voltage-dependent

The mammalian cochlea depends on an amplification process for its sensitivi ty and frequency-resolving capability. Outer hair cells are responsible for providing this amplification. It is usually assumed that the membrane-pote ntial-driven somatic shape changes of these cells are the basis of the ampl ifying process. It is of interest to see whether mechanical reactance chang es of the cells might accompany their changes in cell shape. We now show th at the cylindrical outer hair cells change their axial stiffness as their m embrane potential is altered. Cell stiffness was determined by optoelectron ically measuring the amplitude of motion of a flexible vibrating fiber as i t was loaded by the isolated cell. Voltage commands to the cell were delive red in a tight-seal whole-cell configuration. Cell stiffness was decreased by depolarization and increased by hyperpolarization.