Acetylation and phosphorylation of choline following high or low affinity uptake by rat cortical synaptosomes

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Abstract
Synaptosomal acetylcholine synthesis was found to be dependent on the presence of Na+-dependent HC-3 sensitive choline transport at low (5.5 mM) and high (35 mM) K+ concentrations. However, at 5, 20, and 100 μM choline, choline phosphorylation was proportional to total choline uptake, in the presence or absence of high affinity transport. Only in the presence of eserine (50 μM) did acetylcholine synthesis increase as the choline concentration was elevated from 20 μM to 100 μM, and this effect was observed at low and high K+ concentrations. Our results suggest that: 1) the synthesis of non-surplus synaptosomal ACh is dependent on high affinity choline transport; and 2) choline is equally likely to be phosphorylated after being taken up by low or high affinity transport.