EFFECT OF N,N'-DICYCLOHEXYLCARBODIIMIDE ON COMPARTMENTATION AND RELEASE OF NEWLY SYNTHESIZED AND PREFORMED ACETYLCHOLINE IN TORPEDO SYNAPTOSOMES

Using isolated cholinergic synaptosomes prepared from Torpedo electric organ, we studied the effects of N,N'-dicyclohexylcarbodiimide (DCCD) on acetylcholine (ACh) synthesis, compartmentation, and release after stimulation. Whereas ACh synthesis was unchanged, ACh compartmentatio n inside synaptosomes was affected by the presence of DCCD. In resting conditions, the uptake into the synaptic vesicle pool of newly synthe sized ACh (i.e., [C-14]ACh synthesized in the presence of the drug) wa s progressively and markedly inhibited as the duration of DCCD preincu bation was increased, whereas compartmentation of endogenous ACh was u nchanged in the presence of DCCD. After stimulation, the release of en dogenous ACh from DCCD-treated synaptosomes was similar to that of con trol, in contrast to the release of [C-14]ACh, which was markedly inhi bited. This inhibition was observed whatever the conditions of stimula tion used (gramicidin D, calcium ionophore A23187, or KCl depolarizati on). The study of the compartmentation of [C-14]ACh during stimulation revealed a transfer of highly labeled ACh from the free to the bound ACh compartment in the presence of DCCD, suggesting the existence of s everal ACh subcompartments within the free and bound ACh pools. The pr esent results are discussed in comparison with the previously reported effects of vesamicol (AH5183) on ACh compartmentation and release.