title: Glutamate exocytosis and MARCKS phosphorylation are enhanced by a metabotropic glutamate receptor coupled to a protein kinase C synergistically activated by diacylglycerol and arachidonic acid.
abstract: 4-Aminopyridine evokes repetitive firing of synaptosomes and exocytosis of glutamate by inhibiting a dendrotoxin-sensitive K+ channel responsible for stabilizing the membrane potential. We have shown previously that activation of protein kinase C (PKC) by high concentrations of phorbol ester (4 beta-phorbol dibutyrate) can increase release by inhibiting a dendrotoxin-insensitive ion channel, whereas the metabotropic glutamate receptor (mGluR) agonist (1S,3R)-1-aminocyclopentane-1,3-dicarboxylate [(1S,3R)-ACPD] mimics the action of 4 beta-phorbol dibutyrate, but only in the presence of 2 microM arachidonic acid (AA). In this article, we investigate the role of AA. AA plus (1S,3R)-ACPD is without effect on KCl-induced glutamate exocytosis, indicating that the regulatory pathway acts upstream of the release-coupled Ca2+ channel or Ca(2+)-secretion coupling. Diacylglycerol concentrations are greatly enhanced by (1S,3R)-ACPD alone, independently of AA, indicating that AA acts downstream of phospholipase C. Myristoylated alanine-rich C kinase substrate (MARCKS) is the major presynaptic substrate for PKC. mGluR activation by (1S,3R)-ACPD enhances phosphorylation of MARCKS, but only in the presence of AA. These results strongly suggest that AA acts on presynaptic PKC synergistically with diacylglycerol generated by the phospholipase-coupled mGluR, consistent with the known behaviour of certain purified PKC isoforms. The magnitude of the effects observed in a population of rat cerebrocortical synaptosomes suggests that this is a major mechanism regulating the release of the brain's dominant excitatory neurotransmitter and supports the concept that AA, or a related compound with a similar locus of action, may in certain circumstances play a role in synaptic plasticity.
authors.affiliation: Department of Biochemistry, University of Dundee, Scotland, U.K.
authors.forename: E T
authors.initials: ET
authors.lastname: Coffey
authors.forename: I
authors.initials: I
authors.lastname: Herrero
authors.forename: T S
authors.initials: TS
authors.lastname: Sihra
authors.forename: J
authors.initials: J
authors.lastname: Sánchez-Prieto
authors.forename: D G
authors.initials: DG
authors.lastname: Nicholls
mesh_terms: D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D002118:Calcium / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism*; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004075:Diglycerides / Q000378:metabolism*; D004357:Drug Synergism; D004789:Enzyme Activation; D005089:Exocytosis; D018698:Glutamic Acid / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008297:Male; D008565:Membrane Proteins; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D009498:Neurotoxins / Q000494:pharmacology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D011506:Proteins / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000819:agonists / Q000378:metabolism*; D013574:Synaptosomes / Q000378:metabolism*
chemical_list: D004075:Diglycerides; D047908:Intracellular Signaling Peptides and Proteins; C000619712:Marcks protein, rat; D008565:Membrane Proteins; D009498:Neurotoxins; D011506:Proteins; D018094:Receptors, Metabotropic Glutamate; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D000076250:Myristoylated Alanine-Rich C Kinase Substrate; D016718:Arachidonic Acid; D018698:Glutamic Acid; D011493:Protein Kinase C; D002118:Calcium