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Cyclic AMP‐Mediated Enhancement of High‐Affinity Choline Transport and Acetylcholine Synthesis in Brain
Author(s) -
Vogelsberg V.,
Neff N. H.,
Hadjiconstantinou M.
Publication year - 1997
Publication title -
journal of neurochemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.75
H-Index - 229
eISSN - 1471-4159
pISSN - 0022-3042
DOI - 10.1046/j.1471-4159.1997.68031062.x
Subject(s) - cycloheximide , forskolin , acetylcholine , medicine , endocrinology , choline , chemistry , adenylyl cyclase , protein kinase a , cholinergic , phosphodiesterase , cyclase , okadaic acid , phosphatase , biology , biochemistry , phosphorylation , enzyme , stimulation , protein biosynthesis
Intracerebroventricular administration of N 6 , 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 V max without a change of the K m 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.