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. 2006 Dec 28;143(4):905-10.
doi: 10.1016/j.neuroscience.2006.08.025. Epub 2006 Sep 26.

The role of extracellular calcium in exo- and endocytosis of synaptic vesicles at the frog motor nerve terminals

A L Zefirov  1 , M M Abdrakhmanov, M A Mukhamedyarov, P N Grigoryev
Affiliations

The role of extracellular calcium in exo- and endocytosis of synaptic vesicles at the frog motor nerve terminals

A L Zefirov et al. Neuroscience. .

Abstract

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 Ca2+ ions with other bivalent cations (Sr2+, Ba2+, Cd2+, Mg2+) or used a calcium-free solution and monitored fluorescent staining of the nerve terminals in the presence of caffeine, which promotes the release of Ca2+ 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 Ca2+ 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 Ca2+ from intracellular stores. The effect of extracellular Ca2+ on endocytosis might be driven by the non-specific interactions with membrane lipids.

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