Meyer J, Furness D N, Zenner H P, Hackney C M, Gummer A W
Department of Otolaryngology, Section of Physiological Acoustics and Communication, University of Tübingen, 72076 Tübingen, Germany.
J Neurosci. 1998 Sep 1;18(17):6748-56. doi: 10.1523/JNEUROSCI.18-17-06748.1998.
The mechanosensitive transducer channels of hair cells have long been proposed to be gated directly by tension in the tip links. These are thin, elastic extracellular elements connecting the tips of adjacent stereocilia located on the apical surface of the cell. If this hypothesis is true, the channels should close after destruction of tip links. The hypothesis was tested pharmacologically using receptor currents obtained in response to mechanical stimulation of the stereociliary bundle of outer hair cells isolated from the adult guinea pig cochlea. Application of elastase (20 U/ml) or 1,2-bis(2-aminophenoxy)ethane-N,N,N', N'-tetra-acetic acid (BAPTA; 5 mM), both of which are known to disrupt tip links in other hair-cell preparations, led to the expected irreversible loss of receptor currents. However, the cells then displayed a maintained inward current, implying that channels were left permanently open. This current was similar in magnitude to the receptor current before treatment and was reduced reversibly by known blockers of mechanosensitive channels, namely, dihydrostreptomycin (100 microM), amiloride (300 microM), and gadolinium ions (1 mM). These observations suggest that the maintained current flows through the mechanosensitive channels. Electron microscopical analysis of isolated hair cells, exposed to the same concentrations of elastase or BAPTA as in the electrophysiological experiments, demonstrated an almost total loss of tip links in hair bundles that showed no evidence of other mechanical damage. It is concluded that although the tip links are required for mechanoelectrical transduction, the channels are not gated directly by the tip links.
长期以来，人们一直认为毛细胞的机械敏感转导通道是由纤毛顶部连接丝中的张力直接控制门控的。这些连接丝是位于细胞顶端表面的相邻静纤毛顶端之间的细弹性细胞外元件。如果这一假设成立，那么在破坏连接丝后通道应该关闭。利用从成年豚鼠耳蜗分离出的外毛细胞静纤毛束受到机械刺激后产生的受体电流，通过药理学方法对这一假设进行了验证。应用弹性蛋白酶（20 U/ml）或1,2-双（2-氨基苯氧基）乙烷-N,N,N',N'-四乙酸（BAPTA；5 mM），已知这两种物质在其他毛细胞制剂中会破坏连接丝，导致受体电流出现预期的不可逆损失。然而，这些细胞随后表现出持续的内向电流，这意味着通道一直处于永久开放状态。该电流的大小与处理前的受体电流相似，并且可被机械敏感通道的已知阻滞剂，即二氢链霉素（100 μM）、氨氯吡脒（300 μM）和钆离子（1 mM）可逆性降低。这些观察结果表明，持续电流是通过机械敏感通道流动的。对分离出的毛细胞进行电子显微镜分析，这些毛细胞暴露于与电生理实验中相同浓度的弹性蛋白酶或BAPTA中，结果显示毛束中的连接丝几乎完全丧失，且未发现其他机械损伤的迹象。得出的结论是，尽管机械电转导需要连接丝，但通道并非直接由连接丝控制门控。
