Bennett M R, Gibson W G, Poznanski R R
Department of Physiology, University of Sydney, New South Wales, Australia.
Philos Trans R Soc Lond B Biol Sci. 1993 Oct 29;342(1300):89-99. doi: 10.1098/rstb.1993.0140.
A discrete model has been developed that describes the extracellular current that flows in a smooth muscle syncytium upon the secretion of a quantum of transmitter onto a smooth muscle cell in the syncytium. This allows a description to be given of the current (called the excitatory junctional current (EJC)) recorded by an electrode of given diameter placed on the surface of the muscle, during synaptic transmission from a varicosity situated anywhere in the muscle. The EJC is of maximum negative amplitude when the varicosity is at the surface of the muscle near the inside rim of the electrode and decreases as the varicosity moves to the centre of the electrode. It is of maximum positive amplitude when the varicosity is at the surface near the outside rim of the electrode and declines rapidly in amplitude as the varicosity is removed further from the outside rim. Smaller diameter electrodes give larger EJCs than larger diameter electrodes for most positions of the varicosity on the surface of the muscle. The EJC amplitude declines for varicosities beneath the electrode that are not on the surface of the muscle, but deep in the tissue. The rate of this decline is greater the smaller the diameter of the electrode. The time-course of the EJC is largely invariant under changes in the position of the varicosity with respect to the recording electrode. Changes in the polarity of the current flow during a single EJC can occur, however, if two varicosities secrete transmitter simultaneously, one inside the electrode and one outside, and the time-course of the currents due to the individual varicosities is either the same or slightly different. This theoretical work has been used to interpret a number of recent experimental studies of extracellular current flow during autonomic neuromuscular transmission.
已经开发出一种离散模型，该模型描述了在将一定量的递质分泌到平滑肌合胞体中的一个平滑肌细胞上时，在平滑肌合胞体中流动的细胞外电流。这使得能够描述在突触传递过程中，当曲张体位于肌肉中任何位置时，放置在肌肉表面的给定直径电极所记录的电流（称为兴奋性接头电流（EJC））。当曲张体位于靠近电极内边缘的肌肉表面时，EJC具有最大负振幅，并且随着曲张体向电极中心移动而减小。当曲张体位于靠近电极外边缘的表面时，EJC具有最大正振幅，并且随着曲张体远离外边缘进一步移动，其振幅迅速下降。对于肌肉表面上曲张体的大多数位置，较小直径的电极比较大直径的电极产生更大的EJC。对于不在肌肉表面而是在组织深处的电极下方的曲张体，EJC振幅会下降。电极直径越小，这种下降速率越大。EJC的时间进程在曲张体相对于记录电极的位置变化时基本不变。然而，如果两个曲张体同时分泌递质，一个在电极内部，一个在电极外部，并且由于各个曲张体产生的电流的时间进程相同或略有不同，则在单个EJC期间电流流动的极性可能会发生变化。这项理论工作已被用于解释最近一些关于自主神经肌肉传递过程中细胞外电流流动的实验研究。
