On the Mechanism of Acetylcholine Release

Abstract

Publisher Summary This chapter discusses the mechanism of acetylcholine (ACh) release. Studies show that the electric organ contains high amounts of acetylcholine (ACh) and the enzyme acetylcholinesterase; tissue ACh was shown to be released by stimulating the nerves in the presence of eserine; moreover, an intra-arterial injection of exogenous ACh generated a strong electrical response. The electric organ of Torpedo is a purely cholinergic tissue, from which synaptic vesicles and synaptosomes can be isolated and purified. Most of the tissue acetylcholine (ACh) is localized in nerve terminals, but only a part of it is found to be associated with synaptic vesicles. The remaining ACh, about half of the total store, is extravesicular most probably axoplasmic. Upon nerve stimulation, the axoplasmic pool of ACh is preferentially used and renewed from external precursors. Its level is found to undergo dramatic oscillations during synaptic activity. In contrast, the vesicular ACh remains stable during the first stages of stimulation, provided that the experiment is performed under physiological conditions. Therefore, the axoplasmic ACh appears as the compartment of transmitter available for release during synaptic activity. A quantitative description is proposed of the changes occurring during repetitive stimulation of the electric organ.