Arachidonic acid inhibits uptake of amino acids and potentiates PKC effects on glutamate, but not GABA, exocytosis in isolated hippocampal nerve terminals.
Arachidonic acid (AA), the putative retrograde messenger in long-term potentiation, enhanced extracellular aspartate, glutamate, and GABA levels in rat hippocampus synaptosomes. Whether this effect was determined by stimulating the release and/or inhibiting the uptake of amino acids was further investigated using different experimental conditions. To approach physiological conditions, a static incubation assay was used where both release and uptake occur. Under these conditions, AA dose-dependently (10-25 microM) enhanced basal extracellular amino acid levels in a completely Ca2+-independent way. AA still exerted this effect in the presence of inhibitors of PKC or of AA metabolism. When using the superfusion release assay, in which amino acid uptake cannot occur, no potentiating effect of AA on superfusate amino acid levels was observed. Therefore, AA possibly enhances the extracellular levels of aspartate, glutamate and GABA by inhibiting the uptake of these amino acids and not their efflux. Indeed, AA reduced the Na+-dependent uptake of endogenously released amino acids, which were labelled with traces of tritiated D-aspartate and GABA. When stimulating hippocampus synaptosomes with 4-aminopyridine, AA (2 microM) potentiated the Ca2+-dependent release of glutamate, but not of GABA, synergistically with PKC activation by 4beta-phorbol-12,13-dibutyric acid. In rat hippocampus, AA exerts different presynaptic effects to regulate extracellular amino acid levels, by inhibiting carrier-mediated uptake and, for glutamate, by stimulating exocytosis.
Breukel
A I
AI
Graduate School of Neurosciences, Institute for Neurobiology, University of Amsterdam, The Netherlands.
Besselsen
E
E
Lopes da Silva
F H
FH
Ghijsen
W E
WE
D015761:4-Aminopyridine / Q000494:pharmacology; D000244:Adenosine Diphosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000378:metabolism; D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D016718:Arachidonic Acid / Q000494:pharmacology*; D001224:Aspartic Acid / Q000378:metabolism; D001692:Biological Transport / Q000187:drug effects; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology; D018698:Glutamic Acid / Q000378:metabolism*; D006624:Hippocampus / Q000502:physiology*; D007213:Indomethacin / Q000494:pharmacology; D007700:Kinetics; D007770:L-Lactate Dehydrogenase / Q000032:analysis; D008297:Male; D009637:Masoprocol / Q000494:pharmacology; D009411:Nerve Endings / Q000187:drug effects / Q000502:physiology*; D015240:Phorbol 12,13-Dibutyrate / Q000494:pharmacology; D011493:Protein Kinase C / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar; D012964:Sodium / Q000494:pharmacology; D013574:Synaptosomes / Q000187:drug effects / Q000502:physiology*; D005680:gamma-Aminobutyric Acid / Q000378:metabolism*
D000596:Amino Acids; D016718:Arachidonic Acid; D001224:Aspartic Acid; D015240:Phorbol 12,13-Dibutyrate; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D000244:Adenosine Diphosphate; D009637:Masoprocol; D000255:Adenosine Triphosphate; D012964:Sodium; D015761:4-Aminopyridine; D007770:L-Lactate Dehydrogenase; D011493:Protein Kinase C; D007213:Indomethacin