Beutner D, Voets T, Neher E, Moser T
Department of Membrane Biophysics, Max-Planck-Institute for Biophysical Chemistry, Am Fassberg, 37077, Göttingen, Germany.
Neuron. 2001 Mar;29(3):681-90. doi: 10.1016/s0896-6273(01)00243-4.
Release of neurotransmitter at the inner hair cell (IHC) afferent synapse is a fundamental step in translating sound into auditory nerve excitation. To study the Ca2+ dependence of the underlying vesicle fusion and subsequent endocytosis, we combined Ca2+ uncaging with membrane capacitance measurements in mouse IHCs. Rapid elevations in [Ca2+]i above 8 microM caused a biphasic capacitance increase corresponding to the fusion of approximately 40,000 vesicles. The kinetics of exocytosis displayed a fifth-order Ca2+ dependence reaching maximal rates of >3 x 10(7) vesicle/s. Exocytosis was always followed by slow, compensatory endocytosis (tau congruent with 15 s). Higher [Ca2+]i increased the contribution of a faster mode of endocytosis with a Ca2+ independent time constant of approximately 300 ms. These properties provide for rapid and sustained transmitter release from this large presynaptic terminal.
在内耳毛细胞（IHC）传入突触处神经递质的释放是将声音转化为听神经兴奋的一个基本步骤。为了研究潜在囊泡融合及随后内吞作用对Ca2+的依赖性，我们将Ca2+光解笼锁技术与小鼠IHC的膜电容测量相结合。细胞内Ca2+浓度（[Ca2+]i）快速升高至8微摩尔以上会导致电容呈双相增加，这与约40,000个囊泡的融合相对应。胞吐动力学显示出对Ca2+的五阶依赖性，最大速率超过3×10(7)个囊泡/秒。胞吐作用之后总是伴随着缓慢的、补偿性的内吞作用（时间常数τ约为15秒）。较高的[Ca2+]i增加了一种更快内吞模式的作用，其Ca2+非依赖性时间常数约为300毫秒。这些特性使得这个大的突触前终末能够实现快速且持续的递质释放。
