The Journal of Cell Biology · 1980 · 233 citations · 23 references
Life SciencesNeurobiologyPhysiologyCalcium HomeostasisElectrophysiologyNeuroanatomyCalcium SignalingIntracellular Calcium SignalingNeuromuscular JunctionNeuromuscular PhysiologyNeurotransmitter ReleaseSynaptic Vesicle ReleaseNeuromuscular Junction TransmissionNeuromuscular Synaptic TransmissionPresynaptic Calcium SignalingSnake Venom ToxicologyVenom PharmacologyVenom Secretion
The study applied low doses of crude black widow spider venom or purified alpha‑latrotoxin to frog cutaneous pectoris muscles to examine neuromuscular transmission, quantal secretion, ultrastructural changes, and horseradish peroxidase uptake. In Ca²⁺‑free conditions, alpha‑latrotoxin induced a rapid but transient increase in quantal release followed by irreversible block of transmission and vesicle depletion, whereas in 1.8 mM Ca²⁺ the toxin produced a sustained intermediate release with only partial transmission block and preserved vesicle pools, indicating that Ca²⁺ is essential for endocytosis at the frog neuromuscular junction.
Frog cutaneous pectoris muscles were treated with low doses of crude black widow spider venom (BWSV) or purified alpha-latrotoxin, and neuromuscular transmission, quantal secretion, changes in ultrastructure and uptake of horseradish peroxidase (HRP) were studied. When these agents were applied to muscles bathed in a Ca2+-free solution with 1 mM EGTA and 4 mM Mg2+, the rate of quantal secretion rose to high levels but quickly subsided; neuromuscular transmission was totally and irreversibly blocked within 1 h. The terminals became swollen and were depleted of vesicles; HRP was not taken up. When BWSV was applied to other muscles bathed in a solution with 1.8 mM Ca2+ and 4 mM Mg2+, the rate of secretion rose to high levels and then declined to intermediate levels that were sustained throughot the hour of exposure. Neuromuscular transmission was blocked in fewer than 50% of these fibers. The ultrastructure of these terminals was normal and they contained large numbers of synaptic vesicles. If HRP had been present, most of the synaptic vesicles were labeled with reaction product. These observations suggest that Ca2+ plays an important role in endocytosis at the frog neuromuscular junction.
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