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Factors governing the appearance of small-mode miniature endplate currents at the snake neuromuscular junction.

Authors
  • Prior, C
Type
Published Article
Journal
Brain Research
Publisher
Elsevier
Publication Date
Nov 21, 1994
Volume
664
Issue
1-2
Pages
61–68
Identifiers
PMID: 7895047
Source
Medline
License
Unknown

Abstract

At the snake neuromuscular junction, following a short period of high frequency motor nerve stimulation, a population of 'small-mode' miniature endplate currents (MEPCs) is seen. These small-mode MEPCs are believed to be due to the release of acetylcholine from incompletely refilled recycling synaptic vesicles [Searl et al., Neuroscience, 35 (1991) 145-156]. This study determines the role of the trans-vesicular membrane proton gradient in the generation of small-mode MEPCs. Preserving the trans-vesicular membrane proton gradient during synaptic vesicle exocytosis by exposure of snake nerve/muscle preparations to an extracellular pH approximately equal to the intravesicular pH, leads to an augmentation of the amplitude of the stimulation-induced small-mode MEPCs. Conversely, pretreatment of snake neuromuscular preparations with 10 mM ammonium ions, to buffer intravesicular protons and hence dissipate the trans-vesicular membrane proton gradient, leads to an inhibition of the stimulation-induced appearance of small-mode MEPCs. The data are consistent with the theory that the reduced acetylcholine content of recycled synaptic vesicles in the snake is a consequence of an incomplete restoration of the trans-vesicular membrane proton gradient following synaptic vesicle exocytosis. Thus, in recycling synaptic vesicles the limiting step in the refilling process appears to be generation of the trans-membrane proton gradient and not the transport of acetylcholine into the vesicle.

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