Atwood H L, Karunanithi S, Georgiou J, Charlton M P
Department of Physiology, University of Toronto, Ont., Canada.
Invert Neurosci. 1997 Sep-Dec;3(2-3):81-7. doi: 10.1007/BF02480362.
Crustacean and insect neuromuscular junctions typically include numerous small synapses, each of which usually contains one or more active zones, which possess voltage-sensitive calcium channels and are specialized for release of synaptic vesicles. Strength of transmission (the number of quantal units released per synapse by a nerve impulse) varies greatly among different endings of individual neurons, and from one neuron to another. Ultrastructural features of synapses account for some of the physiological differences at endings of individual neurons. The nerve terminals that release more neurotransmitter per impulse have a higher incidence of synapses with more than one active zone, and this is correlated with more calcium build-up during stimulation. However, comparison of synaptic structure in neurons with different physiological phenotypes indicates no major differences in structure that could account for their different levels of neurotransmitter release per impulse, and release per synapse differs among neurons despite similar calcium build-up in their terminals during stimulation. The evidence indicates differences in calcium sensitivity of the release process among neurons as an aspect of physiological specialization.
甲壳类动物和昆虫的神经肌肉接头通常包含许多小突触，每个突触通常含有一个或多个活性区，这些活性区具有电压敏感性钙通道，专门用于释放突触小泡。传递强度（神经冲动在每个突触释放的量子单位数量）在单个神经元的不同末梢之间以及从一个神经元到另一个神经元之间有很大差异。突触的超微结构特征解释了单个神经元末梢的一些生理差异。每个冲动释放更多神经递质的神经末梢具有多个活性区的突触发生率更高，这与刺激期间更多的钙积累相关。然而，对具有不同生理表型的神经元的突触结构进行比较表明，结构上没有重大差异可以解释它们每个冲动释放神经递质的不同水平，并且尽管在刺激期间它们的末梢中钙积累相似，但每个突触的释放量在神经元之间也有所不同。证据表明，作为生理特化的一个方面，神经元之间释放过程的钙敏感性存在差异。
