Adenosine Inhibits Choline Kinase Activity and Decreases the Phosphorylation of Choline in Striatal Synaptosomes

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Abstract
The main objective of these studies was to determine whether adenosine inhibits choline kinase in rat striata, leading to a decreased incorporation of choline into phosphorylcholine, a mechanism that may mediate seizure‐induced increases in the levels of free choline in brain. Incubation of paniculate and soluble fractions of striatal synaptosomes with adenosine or its metabolically stable analogues significantly inhibited enzyme activity. The inhibition was noncompetitive versus choline and competitive versus MgATP. Inhibitor constants for adenosine, 2‐chloroadenosine, and 2′,5′‐dideoxyadenosine at the MgATP site were 94, 49, and 207 μM, respectively; these values were less than the Michaelis constant for MgATP (340 μM). To determine whether adenosine altered the phosphorylation of choline in an intact preparation, synaptosomes were in cubated with [3H]choline in the presence or absence of adenosine or its analogues and the amount of [3H]‐phosphorylcholine formed from the [3H]choline taken up was measured. All compounds tested significantly reduced the synthesis of [3H]phosphorylcholine. Results suggest that following seizures or hypoxia, when levels of adenosine increase and the concentration of ATP decreases, inhibition of choline phosphorylation may be manifest, resulting in increased levels of free choline in brain.

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