Abstract —The release of newly synthesized acetylcholine (ACh) by cortical slices from rat brain in the presence of 25 m m ‐KCl was studied. The slices were incubated for 5 min in a medium containing both [2‐ 14 C]pyruvate and choline labelled with 3 deuterium atoms (choline‐d 3 ) in order to label at the same time the acetyl moiety and the choline moiety of ACh. The non‐labelled ACh and the ACh‐d 3 were measured by pyrolysis‐gas chromatography/mass spectrometry, and the [ I4 C]ACh by liquid scintillation counting. It was found that the newly formed [ 4 C]ACh as well as the newly formed ACh‐d 3 had a more than 2.5 times greater probability of being released than the preformed non‐labelled ACh. These findings strongly suggest that it is not simply the ACh synthesized immediately inside the nerve ending membrane from incoming undiluted labelled choline, which is preferentially released, but that all newly formed ACh has a greater probability of being released than preformed ACh. No preferential release of newly formed ACh was observed when the incubation medium contained 5.6 m m ‐pyruvate instead of 10 m m ‐glucose + 0.6 m m ‐pyruvate. The cause of this difference remains unexplained.
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Molenaar et al. (1976) studied this question.
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