A study I recently analyzed for my sensory neurology course, aimed to find which mechanically-sensitive transducer channels allow hair cells to detect vibrations. The channels are believed to activate as a result of deflection towards the tallest stereociliary row. This is caused by a force applied by extracellular tip-links. Calcium signals in the first, second, and third stereociliar rows of a rat’s cochlear inner hair cells were visualized by using fast confocal imaging of fluorescence changes that reflect calcium entry during stereociliary bundle stimulation. Calcium was the ion of choice because hair cell channels have shown to be highly permeable to it. Individual stereocilia were imaged at the apical portion of the bundle and indicator dyes with a range of affinities were used. The results from these experiments indicated there are no channels in first row stereocilia therefore suggesting channels that detect vibrations of the stereociliary bundle are only present at the bottom of tip-links.
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