Kriebel M E, Keller B
Department of Neuroscience and Physiology, SUNY HSC at Syracuse, New York 13210, USA.
Cell Biol Int. 1999;23(8):527-32. doi: 10.1006/cbir.1999.0411.
Exocytosis of a single vesicle has been proposed as the mechanism which determines quantal size by releasing a prepackaged and standard amount of acetylcholine. As first described by del Castillo and Katz (1954) the endplate potential is composed of 100 unitary events and the small variance suggests a binomial release from 100 "discrete patches of membrane". However, exocytosis of 100 vesicles selected randomly from 5000 docked vesicles would yield a variance that is 7 times greater than observed values. We propose that the presynaptic ridge with its compliment of docked vesicles functions as the "discrete patch of membrane" such that arrays of calcium activated fusion pores meter transmitter to form the unit of release. A model based on the synchronous flicker of a large number of fusion pores produces the small variance of both miniature end plate potentials and unitary end plate potentials. Release from a single locus (fusion pore) would generate the sub-MEPP. This model permits vesicle trafficking and vesicular content depletion during tetanic stimulation and explains the frequency dependency of MEPP amplitudes and changes in sub-MEPP to bell-MEPP class ratios.
单个囊泡的胞吐作用被认为是通过释放预先包装好的标准量乙酰胆碱来决定量子大小的机制。正如德尔卡斯蒂略和卡茨（1954年）首次描述的那样，终板电位由100个单位事件组成，小方差表明从100个“离散膜片”进行二项式释放。然而，从5000个停靠的囊泡中随机选择100个囊泡进行胞吐作用，其方差将比观测值大7倍。我们提出，带有停靠囊泡的突触前嵴起到“离散膜片”的作用，使得钙激活融合孔阵列计量递质以形成释放单位。基于大量融合孔同步闪烁的模型产生了微小终板电位和单位终板电位的小方差。从单个位点（融合孔）释放会产生亚微型终板电位。该模型允许在强直刺激期间囊泡运输和囊泡内容物耗尽，并解释了微小终板电位幅度的频率依赖性以及亚微型终板电位与钟形终板电位类别比率的变化。
