Furness D N, Karkanevatos A, West B, Hackney C M
MacKay Institute of Communication and Neuroscience, School of Life Sciences, Keele University, Staffordshire ST5 5BG, UK.
Hear Res. 2002 Nov;173(1-2):10-20. doi: 10.1016/s0378-5955(02)00584-1.
Calmodulin is found in the mechanosensitive stereociliary bundle of hair cells where it plays a role in various calcium-sensitive events associated with mechanoelectrical transduction. In this study, we have investigated the ultrastructural distribution of calmodulin in the apex of guinea-pig cochlear hair cells, using post-embedding immunogold labelling, in order to determine in more detail where calmodulin-dependent processes may be occurring. Labelling was found in the cuticular plate as well as the hair bundle, the rootlets of the stereocilia being more densely labelled than the surrounding filamentous matrix. In the bundle, labelling was found almost exclusively at the periphery rather than over the centre of the actin core of the stereocilia, and was clearly associated with the attachments of the lateral links that connect them to their nearest neighbours. It was also found to be denser towards the tips of stereocilia compared to other stereociliary regions and occurred consistently at either end of the tip link that connects stereocilia of adjacent rows. The contact region between stereocilia that is found just below the tip link was also clearly labelled. These concentrations of labelling in the bundle are likely to indicate sites where calmodulin is associated with calcium/calmodulin-sensitive proteins such as the various myosin isoforms and the plasma membrane ATPase (PMCA2a) that are known to occur there, and possibly with the transduction channels themselves. At least one of the myosin isoforms, myosin 1c, is thought to be associated with slow adaptation, and PMCA2a with control of calcium levels in the bundle. The concentration of calmodulin in the contact region further supports the suggestion that this is a functionally distinct region rather than a simple geometrical association between adjacent stereocilia.
钙调蛋白存在于毛细胞的机械敏感静纤毛束中，在与机械电转导相关的各种钙敏感事件中发挥作用。在本研究中，我们使用包埋后免疫金标记技术，研究了豚鼠耳蜗毛细胞顶端钙调蛋白的超微结构分布，以便更详细地确定钙调蛋白依赖性过程可能发生的位置。在表皮板以及毛束中发现了标记，静纤毛的小根比周围的丝状基质标记更密集。在毛束中，标记几乎只出现在周边，而不是静纤毛肌动蛋白核心的中心，并且明显与将它们连接到最近邻的横向连接的附着有关。与其他静纤毛区域相比，在静纤毛尖端标记也更密集，并且始终出现在连接相邻排静纤毛的尖端连接的两端。在尖端连接下方发现的静纤毛之间的接触区域也有明显标记。毛束中这些标记的集中可能表明钙调蛋白与钙/钙调蛋白敏感蛋白相关的位点，如已知存在于那里的各种肌球蛋白异构体和质膜ATP酶（PMCA2a），也可能与转导通道本身有关。至少一种肌球蛋白异构体，肌球蛋白1c，被认为与缓慢适应有关，而PMCA2a与控制毛束中的钙水平有关。接触区域中钙调蛋白的集中进一步支持了这样的观点，即这是一个功能上不同的区域，而不是相邻静纤毛之间简单的几何关联。
