Stiffness of sensory-cell hair bundles in the isolated guinea pig cochlea.

Stiffness of hair bundles on cochlear hair cells was measured in turns 2, 3 and 4 of isolated preparations of the guinea-pig organ of Corti maintained in tissue culture medium. Defined as the force required to produce a linear 1.0 micron deflection of the hair-bundle tip, stiffness is greater for deflection in the excitatory than in the inhibitory direction. The excitatory-to-inhibitory ratio for inner hair cells (IHC) is significantly lower than the ratio for outer hair cells (OHC). Hair-bundle stiffness decreases radially from the first to third rows of OHC. Over the measurement range of 9.0-18.0 mm from the stapes hair-bundle stiffness decreases much more for OHC (88-97%) than for IHC (50%). Although an increase in hair-bundle length with distance from the stapes accounts for some of the observed stiffness decrease, the major decrease is due to an increase in compliance of the sensory-hair attachment to the hair-cell surface.