Disorganisation of quantal acetylcholine release by zinc at the Torpedo nerve-electroplate junction.
The effects of zinc (Zn2+) on quantal acetylcholine release at the Torpedo nerve-electroplate junction were analysed by using loose patch electrodes designed to record evoked and spontaneous electroplate currents in a delimited area (electrode diameter of 10-15 microm) of the synaptic region. Zn2+ reduced the amplitude, prolonged the synaptic delay and slowed down the rising phase of all-or-none electroplate currents (EPCs) generated in response to activation of Na+ channels in a preterminal nerve branch. In graded EPCs (generated in response to direct activation of terminal Ca2+ channels), Zn2+ caused a reduction of quantal content but no change in the quantal size or in the minimum synaptic delay. The rise time of graded EPCs was prolonged but their half-decay time was not affected. Miniature EPCs (MEPCs) in control preparations had a widely distributed amplitude distribution but a homogeneous and rapid time course. Conversely, MEPCs in Zn2+-treated tissue exhibited a homogeneous and small amplitude, but a prolonged and more variable time course. Zn2+ at 1 mM caused, by itself, a high occurrence of MEPCs under conditions (flat-edged electrodes) when MEPCs are normally very infrequent. It is concluded that Zn2+ can both activate and inhibit the release mechanism and Zn2+-induced quanta exhibit an abnormal time course. The activation of the release process by Zn2+ or by Ca2+ may result in the production of quanta with different kinetics.
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Département de pharmacologie, CMU, CH-1211 Geneva 4, Switzerland.
Dunant
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D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002799:Cholinergic Fibers / Q000187:drug effects / Q000378:metabolism*; D004557:Electric Organ / Q000187:drug effects / Q000502:physiology; D005071:Evoked Potentials / Q000187:drug effects; D012964:Sodium / Q000378:metabolism; D009435:Synaptic Transmission / Q000187:drug effects*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D014101:Torpedo; D015032:Zinc / Q000494:pharmacology*
D013779:Tetrodotoxin; D012964:Sodium; D015032:Zinc; D000109:Acetylcholine