Eisen Marc D, Spassova Maria, Parsons Thomas D
Department of Clinical Studies, New Bolton Center, University of Pennsylvania School of Veterinary Medicine, 382 West Street Road, Kennett Square, PA 19348, USA.
J Neurophysiol. 2004 Jun;91(6):2422-8. doi: 10.1152/jn.01130.2003. Epub 2004 Jan 28.
Hearing requires the hair cell synapse to maintain notable temporal fidelity (< or =1 ms) while sustaining neurotransmitter release for prolonged periods of time (minutes). Here we probed the properties and possible anatomical substrate of prolonged neurotransmitter release by using electrical measures of cell surface area as a proxy for neurotransmitter release to study hair cell exocytosis evoked by repetitive stimuli. We observed marked depression of exocytosis by chick tall hair cells. This exocytic depression cannot be explained by calcium current inactivation, presynaptic autoinhibition by metabotropic glutamate receptors, or postsynaptic receptor desensitization. Rather, cochlear hair cell exocytic depression resulted from the exhaustion of a functional vesicle pool. This releasable vesicle pool is large, totaling approximately 8,000 vesicles, and is nearly 10 times greater than the number of vesicles tethered to synaptic ribbons. Such a large functional pool suggests the recruitment of cytoplasmic vesicles to sustain exocytosis, important for maintaining prolonged, high rates of neural activity needed to encode sound.
听觉要求毛细胞突触在长时间（数分钟）维持神经递质释放的同时保持显著的时间保真度（≤1毫秒）。在这里，我们通过使用细胞表面积的电学测量作为神经递质释放的替代指标，来探究长时间神经递质释放的特性和可能的解剖学基础，以研究重复刺激诱发的毛细胞胞吐作用。我们观察到雏鸡高毛细胞的胞吐作用明显抑制。这种胞吐抑制不能用钙电流失活、代谢型谷氨酸受体的突触前自身抑制或突触后受体脱敏来解释。相反，耳蜗毛细胞的胞吐抑制是由功能性囊泡池的耗尽导致的。这个可释放囊泡池很大，总计约8000个囊泡，几乎是与突触带相连的囊泡数量的10倍。如此大的功能池表明募集了细胞质囊泡来维持胞吐作用，这对于维持编码声音所需的长时间、高频率神经活动很重要。
