Botulinum neurotoxin inhibits the release of newly synthesized acetylcholine from torpedo electric organ synaptosomes

In previous reports, we have shown that botulinum neurotoxin inhibits acetylcholine release from Torpedo marmorata electric organ and from its synaptosomal fraction. Here, we have focussed our attention on the study of the effect of botulinum neurotoxin on the metabolism of acetylcholine, namely, the precursors supply, the synthesis activity and the storage of the neurotransmitter into nerve endings isolated from Torpedo electric organ. Radiolabelled acetylcholine precursors (acetate and choline) uptake, choline O-acetyltransferase activity, and the compartmentalization of the transmitter into the synaptosomes were not modified by botullinum neurotoxin. When labelled nerve ending were depolarized by K⁺, the specific radioactivity of acetylcholine in the free pool fell markedly, but the specific radioactivity in the bound pool remained constant. Botulinum neurotoxin prevented this K⁺-induced decrease of specific radioactivity in the free pool.