Studies on a Possible Functional Coupling Between Presynaptic Acetylcholinesterase and High-Affinity Choline Uptake in the Rat Brain

The relationships between presynaptic acetylcholinesterase (AChE) and high-affinity choline uptake (HACU) were investigated using a monolayer of rat cortex synaptosomes in superfusion conditions. The following sets of experiments were performed: determination of 3H]choline (3H]Ch) uptake during superfusion with 3H]Ch; determination of 3H]Ch uptake during superfusion with acetylcholine (ACh) tritiated in the Ch moiety; evaluation of ACh hydrolysis during superfusion with ACh labelled in the acetate moiety; and comparison of the uptake of 3H]Ch generated by hydrolysis of 3H]ACh with that occurring during superfusion with 3H]Ch. Intact ACh was not taken up by superfused synaptosomes. The uptake of 3H]Ch during superfusion with 1 or 0.1 microM N-methyl-3H]ACh was two-thirds of that occurring during superfusion with the same concentrations of 3H]Ch. The amount of 3H]Ch produced by hydrolysis during 16 min of superfusion was 1/25 of the amount passing through the synaptosomal monolayer during 16 min of superfusion with 3H]Ch. The results indicate that presynaptic AChE and HACU are located in close proximity to each other on the cholinergic terminal membrane, an observation suggesting the possibility of a functional coupling between the two mechanisms.