Department of Integrative Biology and Physiology, University of California, Los Angeles, CA 90095-1606, USA.
J Assoc Res Otolaryngol. 2012 Feb;13(1):39-54. doi: 10.1007/s10162-011-0304-1. Epub 2011 Nov 29.
Using whole-cell patch-clamp recordings, we measured changes in membrane capacitance (ΔC (m)) in two subsets of hair cells from the leopard frog amphibian papilla (AP): the low-frequency (100-500 Hz), rostral hair cells and the high-frequency (500-1200 Hz), caudal hair cells, in order to investigate tonotopic differences in exocytosis. Depolarizations of both rostral and caudal hair cells evoked robust ΔC (m) responses of similar amplitude. However, the calcium dependence of release, i.e., the relationship between ΔC (m) relative to the amount of calcium influx (Q (Ca) (2+)), was found to be linear in rostral hair cells but supra-linear in caudal hair cells. In addition, the higher numbers of vesicles released at caudal hair cell active zones suggests increased temporal precision of caudal hair cell exocytosis. ΔC (m) responses were also obtained in response to sinusoidal stimuli of varying frequency, but neither rostral nor caudal hair cell ΔC (m) revealed any frequency selectivity. While all AP hair cells express both otoferlin and synaptotagmin IV (SytIV), we obtained evidence of a tonotopic distribution of the calcium buffer calretinin which may further increase temporal resolution at the level of the hair cell synapse. Our findings suggest that the low (rostral) and high (caudal) frequency hair cells apply different mechanisms for fine-tuning exocytosis.
使用全细胞膜片钳记录技术，我们测量了来自豹蛙听壶的两个毛细胞亚群（100-500Hz 的低频毛细胞和 500-1200Hz 的高频毛细胞）的膜电容变化（ΔC（m）），以研究胞吐作用的音位差异。两种毛细胞的去极化都引发了幅度相似的强大的 ΔC（m）反应。然而，释放的钙依赖性，即 ΔC（m）与钙流入量（Q（Ca）（2+））的关系，在高频毛细胞中是线性的，但在低频毛细胞中是超线性的。此外，高频毛细胞活性区释放的囊泡数量较多，这表明高频毛细胞胞吐作用的时间精度增加。还可以针对不同频率的正弦刺激获得 ΔC（m）响应，但高频和低频毛细胞的 ΔC（m）均未显示出任何频率选择性。尽管所有的 AP 毛细胞都表达了 otoferlin 和 synaptotagmin IV（SytIV），但我们获得了钙缓冲剂 calretinin 的音位分布证据，这可能会进一步提高毛细胞突触的时间分辨率。我们的发现表明，低频（高频）毛细胞应用不同的机制来微调胞吐作用。
