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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

Authors

  • Eleanor T. Coffey,

    1. Department of Biochemistry, University of Dundee, Dundee, Scotland
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  • Inmaculada Herrero,

    1. Department of Biochemistry, University of Dundee, Dundee, Scotland
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  • Talvinder S. Sihra,

    1. Department of Biochemistry, University of Dundee, Dundee, Scotland
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    • The present address of Dr. T. S. Sihra is Department of Pharmacology, Royal Free Hospital School of Medicine, University of London, London NW3 2PF, U.K.

  • José Sánchez-Prieto,

    1. Department of Biochemistry, University of Dundee, Dundee, Scotland
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    • The present address of Dr. I. Herrero and Dr. J. Sánchez-Prieto is Departamento de Bioquimica, Facultad de Veterinaria, Universidad Complutense de Madrid, Cuidad Universitaria, 28040 Madrid, Spain.

  • David G. Nicholls

    Corresponding author
    1. Department of Biochemistry, University of Dundee, Dundee, Scotland
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Address correspondence and reprint requests to Dr. D. G. Nicholls at Department of Biochemistry, University of Dundee, Dundee DD1 4HN, Scotland, U.K.

Abstract

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 (4β-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 4β-phorbol dibutyrate, but only in the presence of 2 µM 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 Ca2+-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.

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