Arribas M, Blasi J, Lazarovici P, Marsal J. Calcium-dependent and -independent acetylcholine release from electric organ synaptosomes by pardaxin: evidence of a biphasic action of an excitatory neurotoxin.
J Neurochem 1993;
60:552-8. [PMID:
8419536 DOI:
10.1111/j.1471-4159.1993.tb03184.x]
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Abstract
The effect of pardaxin, a new excitatory neurotoxin, on neurotransmitter release was tested using purely cholinergic synaptosomes of Torpedo marmorata electric organ. Pardaxin elicited the release of acetylcholine with a biphasic dose dependency. At low concentrations (up to 3 x 10(-7) M), the release was calcium-dependent and synaptosomal structure was well preserved as revealed by electron microscopy and measurements of occluded lactate dehydrogenase activity. At concentrations from 3 x 10(-7) M to 10(-5) M, the pardaxin-induced release of acetylcholine was independent of extracellular calcium, and occluded synaptosomal lactate dehydrogenase activity was lowered, indicating a synaptosomal membrane perturbation. Electron microscopy of 10(-6) M pardaxin-treated synaptosomes revealed nerve terminals depleted of synaptic vesicles and containing cisternae. At higher toxin concentrations (> or = 10(-5) M), there were striking effects on synaptosomal morphology and occluded lactate dehydrogenase activity, suggesting a membrane lytic effect. We conclude that, at low concentrations, this neurotoxin is a promising tool to investigate calcium-dependent mechanisms of neurotransmitter release in the nervous system.
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