Calcium-Sensing Receptor Is Functionally Expressed in the Cochlear Perilymphatic Compartment and Essential for Hearing
Calcium-Sensing Receptor Is Functionally Expressed in the Cochlear Perilymphatic Compartment and Essential for Hearing
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DOI：
10.3389/fnmol.2019.00175
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发表时间：
2019-07-16
影响因子：
4.8
通讯作者：
Murakami, Shingo
中科院分区：
文献类型：
--
作者：
Minakata, Toshiya;Inagaki, Akira;Murakami, Shingo
维持淋巴液中的Ca 2+稳态对于正常的听力是必要的。尽管其意义，维持耳蜗淋巴Ca 2+浓度在一定范围内的机制并不完全清楚。我们研究了钙敏感受体（CaSR）的功能表达，该受体在感知细胞外Ca 2+浓度进行反馈调节中起着关键作用。CaSR蛋白质印迹法显示约130 kDa的蛋白质表达在耳蜗组织提取物和免疫组化分析显示其表达特异性在I型纤维细胞的螺旋韧带，纤维细胞在supralimbalandlimbal地区，上皮的骨螺旋板，和平滑肌细胞的螺旋蜗轴动脉。Ca 2+成像表明，细胞外Ca 2+增加了螺旋韧带中表达CaSR的纤维细胞的细胞内Ca 2+水平，并且这被CaSR抑制剂NPS 2143抑制。此外，在一定频率范围内（8-32 kHz），脑内应用CaSR抑制剂NPS 2143和Calhex 231可适度提高听力阈值。这些结果证实了耳蜗外淋巴室中CaSR的功能性表达。此外，通过抑制CaSR实现的听力阈值升高表明这是正常听力所需的机制，可能是通过感知外淋巴Ca 2+将Ca 2+浓度稳定在一定范围内。这些结果提供了新的见解的机制，调节耳蜗中的钙离子稳态，并提供了一个新的角度对耳蜗生理。
Maintaining Ca2+ homeostasis in lymphatic fluids is necessary for proper hearing. Despite its significance, the mechanisms that maintain the cochlear lymphatic Ca2+ concentrations within a certain range are not fully clarified. We investigated the functional expression of calcium-sensing receptor (CaSR), which plays a pivotal role in sensing extracellular Ca2+ concentrations for feedback regulations. Western blotting for CaSR revealed an approximately 130-kDa protein expression in cochlear tissue extracts and immunohistochemical analysis revealed its expression specifically in type I fibrocytes in the spiral ligament, fibrocytes in the supralimbal and limbal regions, the epithelium of the osseous spiral lamina, and the smooth muscle cells of the spiral modiolar arteries. Ca2+ imaging demonstrated that extracellular Ca2+ increased the levels of intracellular Ca2+ in CaSR-expressing fibrocytes in the spiral ligament, and that this was suppressed by the CaSR inhibitor, NPS2143. Furthermore, hearing thresholds were moderately elevated by intracochlear application of the CaSR inhibitors NPS2143 and Calhex231, across a range of frequencies (8-32 kHz). These results demonstrate the functional expression of CaSR in the cochlear perilymphatic compartment. In addition, the elevated hearing thresholds that are achieved by inhibiting CaSR suggest this is a required mechanism for normal hearing, presumably by sensing perilymphatic Ca2+ to stabilize Ca2+ concentrations within a certain range. These results provide novel insight into the mechanisms regulating Ca2+ homeostasis in the cochlea and provide a new perspective on cochlear physiology.