Russell I J, Kössl M, Richardson G P
School of Biological Sciences, University of Sussex, Falmer, Brighton, U.K.
Proc Biol Sci. 1992 Dec 22;250(1329):217-27. doi: 10.1098/rspb.1992.0152.
The stiffness of sensory hair bundles of both inner (IHC) and outer (OHC) hair cells was measured with calibrated silica fibres in mouse cochlear cultures to test the hypothesis that the mechanical properties of the hair bundle reflect processes underlying mechanotransduction. For OHCs, the displacement of the hair bundle relaxed with time constants of 6 ms for displacements which open transducer channels and 4 ms for displacements which close the channels. The corresponding values of the time constants for IHCs were 10 ms and 8 ms, respectively. A displacement-dependent change in the stiffness of the hair bundle was not observed when the bundle was displaced orthogonally to the direction of excitation. The stiffness of the hair bundle as a function of nanometre displacements from the resting position was remarkably nonlinear. The stiffness declined to a minimum from the resting stiffness by about 12% for OHCs and 20% for IHCs when the hair bundle was displaced by about 20 nm in the excitatory direction, and it increased by a similar amount when the bundle was displaced by 20 nm in the inhibitory direction. The displacement at which the stiffness reached a minimum was within the most sensitive region of the hair-cell transducer function (receptor potential as a function of hair-bundle displacement), and the displacement at which the stiffness reached a maximum was at the point of saturation of the transducer function in the inhibitory direction. The nonlinear displacement-dependent compliance change is reversibly abolished, and the time constant of relaxation of the bundle for excitatory displacements is reversibly reduced, when mechanotransduction is blocked by the addition of either neomycin sulphate or cobalt chloride to the solution bathing the hair cells. The displacement-dependent compliance change was not apparently reduced when the receptor potential was attenuated through the substitution of sodium in the bathing solution with a less permeant cation, tetraethylammonium. These findings suggest that the nonlinear mechanical properties of the hair bundle are associated with aspects of the hair-cell mechanotransducer process. The mechanical properties of the hair bundle are discussed in relation to the 'gating-spring' hypothesis of hair-cell transduction.
用校准过的石英纤维测量了小鼠耳蜗培养物中内毛细胞（IHC）和外毛细胞（OHC）的感觉毛束的刚度，以检验毛束的机械特性反映机械转导潜在过程这一假设。对于外毛细胞，当打开换能器通道的位移时，毛束的位移以6毫秒的时间常数松弛；当关闭通道的位移时，时间常数为4毫秒。内毛细胞的相应时间常数分别为10毫秒和8毫秒。当毛束垂直于兴奋方向位移时，未观察到毛束刚度随位移的变化。毛束刚度作为从静止位置起纳米级位移的函数，表现出明显的非线性。当毛束在兴奋方向上位移约20纳米时，外毛细胞的刚度从静止刚度下降到最小值，下降了约12%；内毛细胞下降了20%。当毛束在抑制方向上位移20纳米时，刚度增加了类似的量。刚度达到最小值时的位移处于毛细胞换能器功能的最敏感区域内（受体电位作为毛束位移的函数），而刚度达到最大值时的位移处于抑制方向上换能器功能的饱和点。当通过向浴浴毛细胞的溶液中添加硫酸新霉素或氯化钴来阻断机械转导时，与位移相关的顺应性变化被可逆地消除，并且毛束在兴奋位移时的松弛时间常数被可逆地减小。当通过用渗透性较小的阳离子四乙铵替代浴浴溶液中的钠来减弱受体电位时，与位移相关的顺应性变化并未明显减小。这些发现表明，毛束的非线性机械特性与毛细胞机械转导过程的某些方面相关。本文根据毛细胞转导的“门控弹簧”假说来讨论毛束的机械特性。
