Reciprocal regulation of choline acetyltransferase and choline kinase in sympathetic neurons during cholinergic...

The regulation of the synthesis of acetylcholine and phosphatidylcholine in rat sympathetic neurons was examined in the context of cholinergic differentiation. We demonstrate that the activities of choline acetyltransferase (ChAT) and choline kinase (CK) are inversely affected by treatment of sympathetic neurons with retinoic acid, utilized as an agent that induces cholinergic differentiation. Whereas ChAT specific activity increased 2- to 4-fold after 12 days of treatment with 5 microM retinoic acid, CK specific activity decreased by 25-30%. These changes in enzyme activities were essentially reflected in the incorporation of [methyl-3H]choline into ACh and the metabolites of the CDP-choline pathway for phosphatidylcholine synthesis. When sympathetic neurons were treated under high potassium conditions (50 mM) for 12 days, the specific activity of CK increased 1.3-fold whereas the activity of ChAT decreased by up to 90%. Furthermore, experiments in which the incorporation of [methyl-3H]choline into ACh and the metabolites of the CDP-choline pathway was measured in the absence of Na+ or in the presence of hemicholinium-3 (HC-3), demonstrate that CK has access to the same pool of choline utilized by ChAT. These results provide evidence that the activities of ChAT and CK may be inversely regulated during the process of cholinergic differentiation.