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 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.
Zefirov
A L
AL
Department of Physiology, Kazan State Medical University, Butlerov Street 49, Kazan, Russia 420012.
Abdrakhmanov
M M
MM
Mukhamedyarov
M A
MA
Grigoryev
P N
PN
D000818:Animals; D002110:Caffeine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling / Q000187:drug effects / Q000502:physiology*; D002413:Cations, Divalent / Q000494:pharmacology; D000697:Central Nervous System Stimulants / Q000494:pharmacology; D004705:Endocytosis / Q000187:drug effects / Q000502:physiology*; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D045604:Extracellular Fluid / Q000378:metabolism; D005456:Fluorescent Dyes / Q000494:pharmacology; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009046:Motor Neurons / Q000187:drug effects / Q000378:metabolism; D009469:Neuromuscular Junction / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D017729:Presynaptic Terminals / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D011726:Pyridinium Compounds / Q000494:pharmacology; D000644:Quaternary Ammonium Compounds / Q000494:pharmacology; D011895:Rana ridibunda; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology; D013572:Synaptic Vesicles / Q000378:metabolism* / Q000648:ultrastructure
D002413:Cations, Divalent; D000697:Central Nervous System Stimulants; C073804:FM1 43; D005456:Fluorescent Dyes; D011726:Pyridinium Compounds; D000644:Quaternary Ammonium Compounds; D002110:Caffeine; D002118:Calcium