Strength of synaptic transmission at neuromuscular junction of crustaceans and insects in relation to calcium entry |
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Authors: | H L Atwood S Karunanithi J Georgiou M P Charlton |
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Institution: | (1) Department of Physiology, University of Toronto, M5S 1A8 Toronto, Ont, Canada |
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Abstract: | 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. |
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Keywords: | neuromuscular crustacean Drosophila synapse quantal release calcium |
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