Botulinum toxin blocks quantal but not non-quantal release of ACh at the neuromuscular junction

Elis F. Stanley, Daniel B. Drachman

Research output: Contribution to journalArticlepeer-review

39 Scopus citations


Botulinum (BOT) toxin is known to block quantal acetylcholine (ACh) release at the neuromuscular junction but little is known about its effect on non-quantal ACh release. We have examined the effect of BOT on non-quantal ACh release directly using a variant of the electrophysiological technique described by Katz and Miledi6. This method is based on the observation that non-quantally released ACh results in a small, continual depolarization of the postsynaptic membrane, after inhibition of cholinesterase. This depolarization can be revealed by suddenly blocking ACh receptors with a pulse of curare, resulting in an abrupt hyperpolarization, the amplitude of which is presumed to be proportional to the rate of non-quantal ACh release. BOT treatment resulted in a marked decrease in quantal ACh release as shown by miniature endplate potential (m.e.p.p.) frequencies (control 0.65 ± 0.33 m.e.p.p.s/s; BOT 0.03 ± 0.03 m.e.p.p.s/s). However, non-quantal ACh release measured by the curare induced hyperpolarization, was not significantly different in control and BOT treated diaphragms (control 1.01 ± 0.09 mV; BOT 1.03 ± 0.11 mV). Our results show that BOT does not block non-quantal ACh release at a time when it has a profound effect on spontaneous quantal ACh release. This suggests that quantal and non-quantal ACh release take place through different release mechanisms.

Original languageEnglish (US)
Pages (from-to)172-175
Number of pages4
JournalBrain research
Issue number1
StatePublished - Feb 14 1983


  • botulinum toxin
  • neuromuscular junction
  • non-quantal ACh release

ASJC Scopus subject areas

  • General Neuroscience
  • Molecular Biology
  • Clinical Neurology
  • Developmental Biology


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