Beta-bungarotoxin-induced depletion of synaptic vesicles at the mammalian neuromuscular junction.
The neurotoxic phospholipase A(2), beta-bungarotoxin, caused the failure of the mechanical response of the indirectly stimulated rat diaphragm. Exposure to beta-bungarotoxin had no effect on the response of the muscle to direct stimulation. Resting membrane potentials of muscle fibres exposed to the toxin were similar to control values, and the binding of FITC-labelled alpha-bungarotoxin to nAChR at the neuromuscular junction was unchanged. Motor nerve terminal boutons at a third of cell junctions were destroyed by exposure to beta-bungarotoxin leaving only a synaptic gutter filled with Schwann cell processes and debris. At other junctions, some or all boutons survived exposure to the toxin. Synaptic vesicle density in surviving terminal boutons was reduced by 80% and synaptophysin immunoreactivity by >60% in preparations exposed to beta-bungarotoxin, but syntaxin and SNAP-25 immunoreactivity was largely unchanged. Terminal bouton area was also unchanged. The depletion of synaptic vesicles was completely prevented by prior exposure to botulinum toxin C and significantly reduced by prior exposure to conotoxin omega-MVIIC. The data suggest that synaptic vesicle depletion is caused primarily by a toxin-induced entry of Ca(2+) into motor nerve terminals via voltage gated Ca(2+) channels and an enhanced exocytosis via the formation of t- and v-SNARE complexes.
Prasarnpun
S
S
School of Neurology, Neurobiology and Psychiatry, Faculty of Medical Sciences, University of Newcastle upon Tyne, Newcastle upon Tyne NE2 4HH, UK.
Walsh
J
J
Harris
J B
JB
D000110:Acetylcholinesterase / Q000378:metabolism; D000818:Animals; D002038:Bungarotoxins / Q000633:toxicity*; D002118:Calcium / Q000502:physiology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D020013:Calcium Signaling / Q000187:drug effects; D002462:Cell Membrane / Q000187:drug effects; D003964:Diaphragm / Q000294:innervation; D004594:Electrophysiology; D005260:Female; D007150:Immunohistochemistry; D015640:Ion Channel Gating / Q000187:drug effects; D008565:Membrane Proteins / Q000502:physiology; D018613:Microscopy, Confocal; D008854:Microscopy, Electron; D009119:Muscle Contraction / Q000187:drug effects / Q000502:physiology; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000502:physiology; D009469:Neuromuscular Junction / Q000187:drug effects*; D018377:Neurotransmitter Agents / Q000378:metabolism; D010741:Phospholipases A / Q000633:toxicity; D051381:Rats; D017208:Rats, Wistar; D011976:Receptors, Muscarinic / Q000187:drug effects; D050600:SNARE Proteins; D013570:Synaptic Membranes / Q000187:drug effects; D013572:Synaptic Vesicles / Q000187:drug effects*; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins / Q000502:physiology
D002038:Bungarotoxins; D002121:Calcium Channel Blockers; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D018377:Neurotransmitter Agents; D011976:Receptors, Muscarinic; D050600:SNARE Proteins; C494210:Snap25 protein, rat; D050825:Synaptosomal-Associated Protein 25; D033921:Vesicular Transport Proteins; D010741:Phospholipases A; D000110:Acetylcholinesterase; D002118:Calcium