Fig. 5. OHC and IHC hair bundle viscous damping parameter.

(A) Changes in the slope of the phase-frequency curve acquired on an apical turn OHC stereocilia bundle from P14 Strc^+/−/Tecta^−/− (blue circles) and Strc^−/−/Tecta^−/− (red squares) mice. When the acoustically oscillating 10-μm sphere is moved closer to the sensory hair bundles, changes in dΦ/df measured at f_π/2 are negligible. (B and C) In the absence of stereocilin, the damping parameter is significantly reduced in OHCs (B) but unaffected in IHCs (C). Note that cochlear IHC bundles have elevated fluid-like behavior compared to OHCs, since their hydrodynamic frictional drag is reduced compared to OHCs. Data are presented as means ± SEM; *** indicates significant differences in comparison with heterozygous littermate controls, P < 0.05 (by unpaired two-tailed Student’s t test with Welch’s correction); NS indicates nonsignificant differences in comparison with controls, P > 0.05 (by unpaired two-tailed Student’s t test with Welch’s correction); the indicated number of cells used was from seven animals for Strc^+/−/Tecta^−/− (n = 40) and seven animals for Strc^−/−/Tecta^−/− (n = 46) OHCs and from five animals for Strc^+/−/Tecta^−/− (n = 14) and four animals for Strc^−/−/Tecta^−/− (n = 13) IHCs.