Effect of diamide on force generation and axial stiffness of the cochlear outer hair cell.

We found that diamide, which affects spectrin, reduces the axial stiffness of the cochlear outer hair cell, the cylindrically shaped mechanoreceptor cell with a unique voltage-sensitive motility. This effect thus provides a means of examining the relationship between the stiffness and the motility of the cell. For measuring axial stiffness and force production, we used an experimental configuration in which an elastic probe was attached to the cell near the cuticular plate and the other end of the cell was held with a patch pipette in the whole-cell recording mode. Diamide at concentrations of up to 5 mM reduced the axial stiffness in a dose-dependent manner to 165 nN per unit strain from 502 nN for untreated cells. The isometric force elicited by voltage pulses under whole-cell voltage clamp was also reduced to 35 pN/mV from 105 pN/mV for untreated cells. Thus the isometric force was approximately proportional to the axial stiffness. Our observations suggest a series connection between the motor and cytoskeletal elements and can be explained by the area motor model previously proposed for the outer hair cell.