Department of Otolaryngology, Stanford University School of Medicine, Stanford, CA 94304, USA.
Neuron. 2011 Apr 28;70(2):326-38. doi: 10.1016/j.neuron.2011.01.031.
Sensory hair cell ribbon synapses respond to graded stimulation in a linear, indefatigable manner, requiring that vesicle trafficking to synapses be rapid and nonrate-limiting. Real-time monitoring of vesicle fusion identified two release components. The first was saturable with both release rate and magnitude varying linearly with Ca(2+), however the magnitude was too small to account for sustained afferent firing rates. A second superlinear release component required recruitment, in a Ca(2+)-dependent manner, of vesicles not in the immediate vicinity of the synapse. The superlinear component had a constant rate with its onset varying with Ca(2+) load. High-speed Ca(2+) imaging revealed a nonlinear increase in internal Ca(2+) correlating with the superlinear capacitance change, implicating release of stored Ca(2+) in driving vesicle recruitment. These data, supported by a mass action model, suggest sustained release at hair cell afferent fiber synapse is dictated by Ca(2+)-dependent vesicle recruitment from a reserve pool.
感觉毛细胞带状突触以线性、不知疲倦的方式对分级刺激作出反应，这要求囊泡运输到突触的速度要快且无速率限制。囊泡融合的实时监测确定了两个释放成分。第一个是可饱和的，释放速率和幅度都与 Ca(2+)呈线性变化，但幅度太小，无法解释持续的传入纤维发放率。第二个超线性释放成分需要以 Ca(2+)依赖性的方式募集突触附近的囊泡。超线性成分具有恒定的释放率，其起始时间随 Ca(2+)负荷而变化。高速 Ca(2+)成像显示内部 Ca(2+)呈非线性增加，与超线性电容变化相关，表明储存的 Ca(2+)释放驱动囊泡募集。这些数据，得到了一个质量作用模型的支持，表明毛细胞传入纤维突触的持续释放是由 Ca(2+)依赖性的从储备池中募集囊泡来决定的。
