Botulinum toxin type A blocks the morphological changes induced by chemical stimulation on the presynaptic membrane of Torpedo synaptosomes.

Abstract

The action of botulinum neurotoxin on acetylcholine release, and on the structural changes at the presynaptic membrane associated with the transmitter release, was studied by using a subcellular fraction of cholinergic nerve terminals (synaptosomes) isolated from the Torpedo electric organ. Acetylcholine and ATP release were continuously monitored by chemiluminescent methods, To catch the membrane morphological changes, the quick-freezing method was applied. Our results show that botulinum neurotoxin inhibits the release of acetylcholine from these isolated nerve terminals in a dose-dependent manner, whereas ATP release is not affected. The maximal inhibition (70%) is achieved at neurotoxin concentrations as low as 125 pM with an incubation time of 6 min. This effect is not linked to an alteration of the integrity of the synaptosomes since, after poisoning by botulinum neurotoxin type A, they show a nonmodified occluded lactate dehydrogenase activity. Moreover, membrane potential is not altered by the toxin with respect to the control, either in resting condition or after potassium depolarization. In addition to acetylcholine release inhibition, botulinum neurotoxin blocks the rearrangement of the presynaptic intramembrane particles induced by potassium stimulation. The action of botulinum neurotoxin suggests that the intramembrane particle rearrangement is related to the acetylcholine secretion induced by potassium stimulation in synaptosomes isolated from the electric organ of Torpedo marmorata.

Functional reconstitution of KCl-evoked, Ca2+-dependent acetylcholine release system inXenopus oocytes microinjected with presynaptic plasma membranes and synaptic vesicles

“…This neurotoxin has been shown to be active in the electric organ system, either on the whole electric organ (Dolezal et al, 1983) or on isolated synaptosomes . The inhibition values obtained in the chimerical oocytes are similar to those obtained for isolated synaptosomes (approximately 70%; Marsal et al, 1989), and the time necessary for blockade of ACh release is also of the same order (a few minutes). BoNT/A inhibits the quanta1 release , but some authors have reported that non-quanta1 release is also affected (Dolezal et al, 1983).…”

Binding of botulinum neurotoxin to pure cholinergic nerve terminals isolated from the electric organ of Torpedo

“…In previous studies it was demonstrated that botulinum neurotoxin inhibited the A C h release from cholinergic synaptosomes isolated from the electric organ of Torpedo (Marsal et al, , 1988(Marsal et al, , 1989. In the present report it is shown that such an inhibition can be prevented by the preincubation of the synaptosomes with an antiserum anti-PSPM, prior to the addition of BoNTA.…”

Control of neurotransmitter release by an internal gel matrix in synaptic vesicles

“…The existence of both binding sites may explain a differential release of ACh and ATP measured, under special conditions, in cholinergic nerve endings (46,47) or a differential release of catecholamines and ATP from chromaffin cells (48).…”