Calcium-dependent and -independent acetylcholine release from electric organ synaptosomes by pardaxin: evidence of a biphasic action of an excitatory neurotoxin.
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.
Arribas
M
M
Departament de Biologia Cel.lular i Anatomia Patològica, Facultat de Medicina, Universitat de Barcelona, Barcelona, Spain.
Blasi
J
J
Lazarovici
P
P
Marsal
J
J
D000109:Acetylcholine / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004557:Electric Organ / Q000187:drug effects / Q000378:metabolism* / Q000648:ultrastructure; D005397:Fish Venoms / Q000494:pharmacology*; D005412:Flatfishes; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000378:metabolism; D008854:Microscopy, Electron; D009498:Neurotoxins / Q000494:pharmacology*; D011189:Potassium Chloride / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000378:metabolism*; D014101:Torpedo
D005397:Fish Venoms; D009498:Neurotoxins; D011189:Potassium Chloride; C017603:pardaxin; D007770:L-Lactate Dehydrogenase; D000109:Acetylcholine; D002118:Calcium