Differential recruitment of acetylcholine vesicle pools by electrical stimulation and KCl depolarization in cholinergic nerve terminals

Depolarizing stimuli regulate acetylcholine (ACh) storage and release via distinct synaptic vesicle pools in cholinergic terminals, but the mechanisms remain unclear. Here, we examined the effects of preliminary depolarization on choline uptake, ACh synthesis, and release in rat striatal segments using [ 3 H]choline incorporation and [ 3 H]ACh release assays. Preliminary KCl depolarization significantly increased functional high‐affinity choline transporter‐1 (CHT1) availability, enhancing subsequent [ 3 H]choline uptake, [ 3 H]ACh synthesis, and release. In contrast, preliminary electrical stimulation selectively increased evoked [ 3 H]ACh release without affecting choline uptake or tissue ACh content. These results suggest that electrical stimulation primarily mobilizes vesicles from the readily releasable pool (RRP) and recycling pool, whereas KCl depolarization additionally recruits vesicles from the reserve pool and may directly trigger ACh release.