Lateral mechanical coupling of stereocilia in cochlear hair bundles
Lateral mechanical coupling of stereocilia in cochlear hair bundles
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DOI：
10.1016/s0006-3495(01)76231-5
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发表时间：
2001-06-01
影响因子：
3.4
通讯作者：
Ruppersberg, JP
中科院分区：
文献类型：
--
作者：
Langer, MG;Fink, S;Ruppersberg, JP
为了了解内耳转导通道的门控过程，有必要表征和检查静纤毛束超微结构的功能特性。有强有力的证据表明，毛细胞中的转导通道是通过直接拉动所谓的尖端链接来门控的。除了这些尖端链接之外，在扫描和透射电子显微镜中还发现了第二类丝状结构：侧对侧链接，这些链接横向连接发束同一排的静纤毛。本研究集中于通过左右链接连接的最高行静纤毛的机械耦合，使用原子力显微镜 (AFM) 研究出生后大鼠（第 4 天）的外毛细胞 (OHC) 的毛束。尽管出生后大鼠的发束在第 4 天仍不成熟，并且相互连接的交联尚未显示出优先方向，但所研究的 OHC 的发束已经显示出成熟毛细胞的特征性 V 形。在第一个实验中，使用 AFM 尖端扫描单个静纤毛来研究静纤毛的硬度。兴奋方向的弹簧常数为2.5 +/- 0.6 x 10(-3) N/m，而在抑制方向观察到更高的弹簧常数（3.1 +/- 1.5 x 10(-3) N/m）。在第二组实验中，使用 AFM 结合细玻璃纤维测量最高行静纤毛之间的力传递。该纤维局部移位了静纤毛，同时通过 AFM 测量横向传输到相邻未触及的较高静纤毛的力。结果表明，出生后大鼠最高的静纤毛之间存在弱力相互作用。在同一行中未与纤维接触的最近相邻的静纤毛处，施加到单个静纤毛的力下降至 36%。建议从较高的静纤毛传递到同一排的相邻静纤毛的力的大小取决于连杆的方向。预计最大的力传递将出现在互连侧连杆的轴线上。在我们的研究中，表明传递的力很小，因为连接侧连杆的方向非常接近于相对于扫描方向（兴奋-抑制方向）的 90 度角。
For understanding the gating process of transduction channels in the inner ear it is essential to characterize and examine the functional properties of the ultrastructure of stereociliary bundles. There is strong evidence that transduction channels in hair cells are gated by directly pulling at the so-called tip links. In addition to these tip links a second class of filamentous structures was identified in the scanning and transmission electron microscope: the side-to-side links, These links laterally connect stereocilia of the same row of a hair bundle. This study concentrates on mechanical coupling of stereocilia of the tallest row connected by side-to-side links, Atomic Force microscopy (AFM) was used to investigate hair bundles of outer hair cells (OHCs) from postnatal rats (day 4). Although hair bundles of postnatal rats are still immature at day 4 and interconnecting cross-links do not show preferential direction yet, hair bundles of investigated OHCs already showed the characteristic V-shape of mature hair cells. In a first experiment, the stiffness of stereocilia was investigated scanning individual stereocilia with an AFM tip. The spring constant for the excitatory direction was 2.5 +/- 0.6 x 10(-3) N/m whereas a higher spring constant (3.1 +/- 1.5 x 10(-3) N/m) was observed in the inhibitory direction. In a second set of experiments, the force transmission between stereocilia of the tallest row was measured using AFM in combination with a thin glass fiber. This fiber locally displaced a stereocilium while the force laterally transmitted to the neighboring untouched taller stereocilia was measured by AFM. The results show a weak force interaction between tallest stereocilia of postnatal rats. The force exerted to an individual stereocilium declines to 36% at the nearest adjacent stereocilium of the same row not touched with the fiber. It is suggested that the amount of force transmitted from a taller stereocilium to an adjacent one of the same row depends on the orientation of links. Maximum force transmission is expected to appear along the axis of interconnecting side links. In our studies it is suggested that transmitted forces are small because connecting side links are oriented very close to an angle of 90 degrees with respect of the scan direction (excitatory-inhibitory direction).