MOLECULAR BASIS OF TRANSDUCTION IN AUDITORY SENSORY ORGANS

我们使用高性能荧光成像系统来观察细胞外ATP对耳蜗感觉运动受体外毛细胞（OHCs）的毛束的局部应用所引起的细胞内游离Ca2+浓度（[Ca2+]i）的快速变化。同时记录全细胞电流和钙绿-1荧光显示[Ca2+]i双组分增加。在Ca2+最初通过顶膜进入后，第二次更大的，由insp3控制的[Ca2+]i激增发生在毛束的基部。这个细胞内Ca2+释放位点的电镜显示，它与一个独特的内质网（ER）膜和线粒体系统（称为Hensens体）的定位一致。使用共聚焦免疫荧光显微镜，我们发现InsP3受体共享这个位置。与与ATP- P2受体相连的Ca2+动员第二信使系统一致，我们还确定了G蛋白的异构体存在于立体纤毛中。在ATP作用前后监测了电压驱动的细胞形状变化和非线性电容，表明ATP引起的[Ca2+]i升高不干扰OHC电动力机制。这种第二信使信号传导机制绕过立体纤毛的Ca2+清除能力，并在毛束基部瞬间升高[Ca2+]i，在那里它可以潜在地调节参与维持毛束完整性的非常规肌球蛋白同工酶的作用，并可能影响机械转导。毛发感觉细胞，机械转导，电运动，耳蜗放大器，耳廓，外毛细胞，嘌呤能受体。

We used a high-performance fluorescence imaging system to visualize rapid changes in intracellular free Ca2+ concentration ([Ca2+]i) evoked by focal applications of extracellullar ATP to the hair bundle of outer hair cells (OHCs) - the sensory-motor receptors of the cochlea. Simultaneous recordings of the whole-cell current and Calcium Green-1 fluorescence showed a two-component increase in [Ca2+]i. After an initial entry of Ca2+ through the apical membrane, a second and larger, InsP3-gated, [Ca2+]i surge occurred at the base of the hair bundle. Electron microscopy of this intracellular Ca2+ release site showed that it coincides with the localization of a unique system of endoplasmic reticulum (ER) membranes and mitochondria known as Hensens body. Using confocal immunofluorescence microscopy, we showed that InsP3 receptors share this location. Consistent with a Ca2+-mobilizing second messenger system linked to ATP- P2 receptors we also determined that an isoform of G proteins is present in the stereocilia. Voltage-driven cell shape changes and nonlinear capacitance were monitored before and after ATP application, showing that the ATP-evoked [Ca2+]i rise did not interfere with the OHC electromotility mechanism. This second messenger signaling mechanism bypasses the Ca2+- clearance power of the stereocilia and transiently elevates [Ca2+]i at the base of the hair bundle, where it can potentially modulate the action of unconventional myosin isozymes involved in maintaining the hair bundle integrity and potentially influence mechano-transduction. - hair sensory cells, mechano transduction, electromotility, cochlear amplifier, organ of Corti, outer hair cells, purinergic receptors.