Cyclic AMP-mediated enhancement of high-affinity choline transport and acetylcholine synthesis in brain.
Intracerebroventricular administration of N6, 2'-O-dibutyryladenosine 3',5'-cyclic monophosphate (db-cyclic AMP) to mice increased high-affinity choline transport (HAChT) into synaptosomal preparations from the hippocampus, striatum, and frontal cortex in a time- dose-, and brain region-dependent manner. Similar observations were made when the cyclic AMP analogue 8-bromo-cyclic AMP, the adenylyl cyclase activator forskolin, and the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine were administered. Inhibition of phosphatase 1 and 2A, with okadaic acid, increased basal choline transport and enhanced the response to db-cyclic AMP. The early increase of HAChT activity induced by db-cyclic AMP was blocked by H-7 and H-89, protein kinase A inhibitors, but not by cycloheximide, a protein synthesis inhibitor. Kinetic analysis of the early changes of HAChT revealed an increase in the apparent Vmax without a change of the Km for choline. Hemicholinium-3 (HC-3) binding was not altered when studied 1 h after db-cyclic AMP administration. In contrast, HC-3 binding and HAChT activity were both elevated when estimated 3 h after the treatment, and pretreatment with cycloheximide partially prevented the db-cyclic AMP-induced HAChT rise. As evidence that enhanced HAChT is associated with a direct action of cyclic AMP-dependent pathways on the cholinergic nerve terminals, addition of 8-bromocyclic AMP to isolated hippocampal synaptosomes induced an increase of HAChT that was prevented by H-89. Choline acetyltransferase activity was not affected at any time during the studies. The synthesis of acetylcholine, however, was enhanced 1 h after db-cyclic AMP addition. Our studies show that cyclic AMP-mimetic compounds appear to modulate the choline carrier by a dual mode: an early increase of the maximal velocity without a change of the number of HC-3 binding sites and a late rise of transport that is accompanied by an increase of HC-3 binding. We postulate that HAChT and consequently acetylcholine synthesis in vivo is modulated, in part, by protein kinase A.
Vogelsberg
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Neuroscience Program, Ohio State University College of Medicine, Columbus 43210, USA.
Neff
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Hadjiconstantinou
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D000109:Acetylcholine / Q000096:biosynthesis*; D000818:Animals; D001692:Biological Transport; D001921:Brain / Q000378:metabolism*; D003994:Bucladesine / Q000494:pharmacology; D002794:Choline / Q000378:metabolism*; D000242:Cyclic AMP / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D008297:Male; D051379:Mice; D008815:Mice, Inbred Strains; D014018:Tissue Distribution
D003994:Bucladesine; D000242:Cyclic AMP; D002794:Choline; D000109:Acetylcholine