Effects of choline augmentation on acetylcholine synthesis and release in rat atrial minces

The uptake and acetylation of [3H]-choline, as well as the calcium-dependent release of a newly synthesized [3H]-ACh, was studied in a new rat atrial mince preparation. The hemicholinium-3-sensitive uptake and acetylation of [3H]-choline increased as [3H]-choline concentrations were elevated to 100 microM in atrial minces. In contrast, hemicholinium-3-sensitive [3H]-choline uptake was saturated with 15 microM [3H]-choline in brain synaptosomes. The increased atrial [3H]-ACh synthesized in the presence of [3H]-choline augmentation was releasable by 50 mM K+-depolarization in a 1 mM cobalt-sensitive manner. These results suggest that atrial parasympathetic activity may be more sensitive to circulating choline concentrations than brain cholinergic neurons are.