The role of extracellular calcium in exo- and endocytosis of synaptic vesicles at the frog motor nerve terminals
In the present study we combined FM 1-43 imaging and electrophysiological recording of miniature end-plate currents (MEPCs) to determine the role of extracellular calcium in synaptic vesicle exo- and endocytosis at the frog motor nerve terminals. We replaced extracellular Ca 2+ ions with other bival...
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Veröffentlicht in: | Neuroscience 2006-12, Vol.143 (4), p.905-910 |
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Sprache: | eng |
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Zusammenfassung: | In the present study we combined FM 1-43 imaging and electrophysiological recording of miniature end-plate currents (MEPCs) to determine the role of extracellular calcium in synaptic vesicle exo- and endocytosis at the frog motor nerve terminals. We replaced extracellular Ca
2+ ions with other bivalent cations (Sr
2+, Ba
2+, Cd
2+, Mg
2+) or used a calcium-free solution and monitored fluorescent staining of the nerve terminals in the presence of caffeine, which promotes the release of Ca
2+ from intracellular stores. Caffeine has induced FM1-43 internalization only in the presence of bivalent cations in the external solution. The exposure of the neuromuscular junction to caffeine in a calcium-free solution caused a reversible failure of FM 1-43 loading and an increase in the nerve terminal width. This effect of a calcium-free solution was not due to a decrease in exocytosis, because caffeine-induced FM1-43 unloading from the previously loaded nerve terminals, as well as a degree of the MEPCs frequency increase, was unchanged. We conclude that the presence of Ca
2+ or other bivalent cations in extracellular space is necessary for endocytosis but not for exocytosis of synaptic vesicles, while transmitter release is promoted by efflux of Ca
2+ from intracellular stores. The effect of extracellular Ca
2+ on endocytosis might be driven by the non-specific interactions with membrane lipids. |
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ISSN: | 0306-4522 1873-7544 |
DOI: | 10.1016/j.neuroscience.2006.08.025 |