Zhao Jingjing, Yin Ning, Li Geng-Lin
ENT Institute and Department of Otorhinolaryngology, Eye and ENT Hospital, Fudan University, Shanghai, China.
NHC Key Laboratory of Hearing Medicine, Fudan University, Shanghai, China.
Front Cell Neurosci. 2023 Jan 9;16:1064886. doi: 10.3389/fncel.2022.1064886. eCollection 2022.
Hearing organs in the peripheral of different vertebrate species are extremely diverse in shape and function. In particular, while the basilar papilla (BP) is elongated and covers the sounds of both low and high frequencies in turtles and birds, it is round and responds to high frequencies only in frogs, leaving the low frequencies to the amphibian papilla (AP). In this study, we performed patch-clamp recordings in hair cells of both hearing organs in bullfrogs and conducted a comparative study of their ionic currents and exocytosis. Compared to hair cells in AP with a large tetraethylammonium (TEA)-sensitive slow-activating K current ( ), those in BP exhibited a small 4-aminopyridine (4-AP)-sensitive fast-inactivating K current ( ). Furthermore, hair cells in BP exhibited a significantly smaller Ca current with a more positive half-activation voltage (V) and a slower slope of voltage dependency (). In response to step depolarization, exocytosis (ΔC) in BP hair cells was also significantly smaller, but the Ca efficiency, assessed with the ratio between ΔC and Ca charge (Q), was comparable to that of AP hair cells. Finally, we applied a paired-step depolarization and varied the interval in between, and we found that the replenishment of synaptic vesicles was significantly slower in BP hair cells. Together, our findings suggest that hair cells tuned to high frequencies in bullfrogs release less synaptic vesicles and recycle synaptic vesicles more slowly, allowing them to cope well with the large DC component found in their receptor potentials .
不同脊椎动物物种外周的听觉器官在形状和功能上极为多样。特别是，虽然基底乳头（BP）在乌龟和鸟类中是细长的，能覆盖低频和高频声音，但在青蛙中它是圆形的，仅对高频做出反应，低频则由两栖乳头（AP）负责。在本研究中，我们对牛蛙两种听觉器官的毛细胞进行了膜片钳记录，并对它们的离子电流和胞吐作用进行了比较研究。与AP中的毛细胞相比，AP中的毛细胞具有大的四乙铵（TEA）敏感的慢激活钾电流（ ），而BP中的毛细胞表现出小的4-氨基吡啶（4-AP）敏感的快失活钾电流（ ）。此外，BP中的毛细胞表现出明显较小的钙电流，其半激活电压（V）更正，电压依赖性斜率更慢（ ）。响应阶跃去极化时，BP毛细胞中的胞吐作用（ΔC）也明显较小，但用ΔC与钙电荷（Q）的比值评估的钙效率与AP毛细胞相当。最后，我们应用双阶跃去极化并改变其间的间隔，发现BP毛细胞中突触小泡的补充明显更慢。总之，我们的研究结果表明，牛蛙中调谐到高频的毛细胞释放的突触小泡更少，突触小泡循环更慢，从而使它们能够很好地应对其感受器电位中发现的大直流成分 。
