Sustained synaptic-vesicle recycling by bulk endocytosis contributes to the maintenance of high-rate neurotransmitter release stimulated by glycerotoxin.
Glycerotoxin (GLTx), a large neurotoxin isolated from the venom of the sea worm Glycera convoluta, promotes a long-lasting increase in spontaneous neurotransmitter release at the peripheral and central synapses by selective activation of Ca(v)2.2 channels. We found that GLTx stimulates the very high frequency, long-lasting (more than 10 hours) spontaneous release of acetylcholine by promoting nerve terminal Ca(2+) oscillations sensitive to the inhibitor omega-conotoxin GVIA at the amphibian neuromuscular junction. Although an estimate of the number of synaptic vesicles undergoing exocytosis largely exceeds the number of vesicles present in the motor nerve terminal, ultrastructural examination of GLTx-treated synapses revealed no significant change in the number of synaptic vesicles. However, we did detect the appearance of large pre-synaptic cisternae suggestive of bulk endocytosis. Using a combination of styryl dyes, photoconversion and horseradish peroxidase (HRP)-labeling electron microscopy, we demonstrate that GLTx upregulates presynaptic-vesicle recycling, which is likely to emanate from the limiting membrane of these large cisternae. Similar synaptic-vesicle recycling through bulk endocytosis also occurs from nerve terminals stimulated by high potassium. Our results suggest that this process might therefore contribute significantly to synaptic recycling under sustained levels of synaptic stimulation.
Meunier
Frederic A
FA
Molecular Dynamics of Synaptic Function Laboratory, Queensland Brain Institute and School of Biomedical Sciences, The University of Queensland, Brisbane, QLD 4072, Australia. f.meunier@uq.edu.au
Nguyen
Tam H
TH
Colasante
Cesare
C
Luo
Fujun
F
Sullivan
Robert K P
RK
Lavidis
Nickolas A
NA
Molgó
Jordi
J
Meriney
Stephen D
SD
Schiavo
Giampietro
G
D000109:Acetylcholine / Q000378:metabolism; D000818:Animals; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002478:Cells, Cultured; D004705:Endocytosis / Q000187:drug effects*; D019706:Excitatory Postsynaptic Potentials; D015801:Helminth Proteins; D055369:Miniature Postsynaptic Potentials; D009046:Motor Neurons / Q000187:drug effects / Q000473:pathology / Q000502:physiology*; D009469:Neuromuscular Junction / Q000502:physiology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D010369:Pectoralis Muscles / Q000294:innervation* / Q000502:physiology; D011077:Polychaeta; D017729:Presynaptic Terminals; D011898:Ranidae; D012910:Snake Venoms / Q000494:pharmacology; D013572:Synaptic Vesicles / Q000187:drug effects / Q000378:metabolism; D014688:Venoms; D020960:omega-Conotoxins / Q000494:pharmacology
D002121:Calcium Channel Blockers; D015801:Helminth Proteins; D018377:Neurotransmitter Agents; D012910:Snake Venoms; D014688:Venoms; D020960:omega-Conotoxins; C078452:ziconotide; C042564:glycerotoxin; D000109:Acetylcholine