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The Journal of Neuroscience, January 1, 2000, 20(1):140-148
Recovery from Open Channel Block by Acetylcholine during
Neuromuscular Transmission in Zebrafish
Pascal
Legendre1,
Declan W.
Ali2, and
Pierre
Drapeau2
1 Institut des Neurosciences, Centre National de la
Recherche Scientifique, Unité Mixte de Recherche 7624, Université Pierre et Marie Curie, 75252 Paris, France, and
2 Center for Research in Neuroscience, Montreal General
Hospital Research Institute and McGill University, Montreal, Quebec,
Canada H3G 1A4
At larval zebrafish neuromuscular junctions (NMJs), miniature end
plate currents (mEPCs) recorded in vivo have an
unusually fast time course. We used fast-flow application of
acetylcholine (ACh) onto outside-out patches to mimic the effect of
synaptic release onto small numbers of ACh receptor channels (AChRs).
Positively charged ACh acted at hyperpolarized potentials and at
millimolar concentrations as a fast ("flickering") open channel
blocker of AChRs. Because of filtering, the open channel block
resulted in reduced amplitude of single channel currents. Immediately
after brief (1 msec) application (without significant desensitization) of millimolar ACh at hyperpolarized potentials, a slower, transient current appeared because of delayed reversal of the block. This rebound
current depended on the ACh concentration and resembled in time course
the mEPC. A simple kinetic model of the AChR that includes an open
channel-blocking step accounted for our single channel results, as well
as the experimentally observed slowing of the time course of mEPCs
recorded at a hyperpolarized compared with a depolarized potential.
Recovery from AChR block is a novel mechanism of synaptic transmission
that may contribute in part at all NMJs.
Key words:
fast-flow; single channels; nonstationary kinetics; neuromuscular junction; mEPC; locomotion.
Copyright © 2000 Society for Neuroscience 0270-6474/0/201140-09$05.00/0
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