Van der Kloot W, Balezina O P, Molgó J, Naves L A
Department of Physiology and Biophysics, HSC, SUNY 11794-8661.
Pflugers Arch. 1994 Sep;428(2):114-26. doi: 10.1007/BF00374848.
Fluctuation analysis was used to estimate the mean single-channel conductance and the mean channel duration of opening. Miniature endplate currents (MEPCs) were measured with the voltage-clamp technique. The timing of endplate channel opening during the generation of the MEPC was estimated by a deconvolution method. Often all of the channels opened during the rise of the MEPC, but in about half of the examples some 10% of the channels opened after the peak. We studied the effects of acetylcholinesterase (AChE) inhibition with neostigmine, diisopropyl fluorophosphate (DFP) and fasciculin-2. With AChE largely inhibited, the number of channels opening increased as much as fourfold, largely by channels opening in the "tail" that follows the peak of the MEPC. The results were compared to models of MEPC generation. Models did not account well for the pattern of channel opening, particularly after AChE inhibition. In the presence of fasciculin-2, the addition of 2 microM (-)-vesamicol reduced the number of channels opening and shortened the period over which channels were open. One interpretation is that quantal ACh release is not almost instantaneous, but that some of the ACh is released over a period of a millisecond or more and that some of the release is blocked by (-)-vesamicol.
采用涨落分析来估计单通道平均电导和平均开放持续时间。用电压钳技术测量微小终板电流（MEPCs）。通过反卷积方法估计MEPC产生过程中终板通道开放的时间。通常，所有通道在MEPC上升过程中打开，但在约一半的样本中，约10%的通道在峰值后打开。我们研究了新斯的明、二异丙基氟磷酸酯（DFP）和束丝菌素-2对乙酰胆碱酯酶（AChE）的抑制作用。在AChE被大量抑制的情况下，开放通道的数量增加了多达四倍，主要是由于在MEPC峰值后的“尾部”打开的通道。将结果与MEPC产生的模型进行了比较。模型不能很好地解释通道开放模式，特别是在AChE抑制后。在存在束丝菌素-2的情况下，添加2 microM（-）-vesamicol可减少开放通道的数量，并缩短通道开放的时间。一种解释是，量子化的乙酰胆碱释放并非几乎瞬间完成，而是一些乙酰胆碱在一毫秒或更长时间内释放，并且一些释放被（-）-vesamicol阻断。
