Blockade of glutamate transporters leads to potentiation of NMDA receptor current in layer V pyramidal neurons of the rat prefrontal cortex via group II metabotropic glutamate receptor activation.
Membrane currents of layer V pyramidal cells in slices of the rat prefrontal cortex (PFC) were recorded with the patch-clamp technique. In an Mg2+-free superfusion medium l-trans-pyrrolidine-2,4-dicarboxylic acid (PDC), a preferential blocker of astrocytic glutamate transporters, caused inward current due to the activation of NMDA receptors. The blockade of conducted action potentials by tetrodotoxin did not interfere with this effect. ATP was inactive when given alone and potentiated the NMDA-induced current in an Mg2+-containing but not Mg2+-free superfusion medium. Agonists of group I ((S)-3,5-dihydroxyphenylglycine; DHPG) and II ((1R,4R,5S,6R)-4-amino-2-oxabicyclo[3.1.0]hexane-4,6-dicarboxylic acid; LY 379268) metabotropic glutamate receptors (mGluRs) also potentiated responses to NMDA, whereas the group III mGluR agonist L-(+)-2-amino-4-phosphonobutyric acid (L-AP4) did not affect them. In contrast to ATP, PDC evoked inward current in the absence but not in the presence of external Mg2+, when given alone, and facilitated the NMDA effect Mg2+-independently. The PDC-induced facilitation of NMDA responses was blocked by group II ((2S)-2-amino-2-[(1S,2S)-2-carboxycycloprop-1-yl]-3-(xanth-9-yl) propanoic acid; LY 341495), but not group I ((RS)-1-aminoindan-1,5-dicarboxylic acid; AIDA) or III (alpha-methyl-3-methyl-4-phosphonophenylglycine; UBP 1112) mGluR antagonists. In conclusion, the blockade of astrocytic glutamate uptake by PDC may lead to a stimulation of group II mGluRs, while the triggering of exocytotic glutamate release from astrocytes by ATP may cause activation of group I mGluRs, both situated postsynaptically at layer V PFC pyramidal cells. Either group of mGluRs may interact with NMDA receptors in a positive manner.
Oliveira
Joao F
JF
Rudolf-Boehm-Institute of Pharmacology and Toxicology, University of Leipzig, Haertelstrasse 16-18, D-04107 Leipzig, Germany.
Krügel
Ute
U
Köles
Laszlo
L
Illes
Peter
P
Wirkner
Kerstin
K
D000255:Adenosine Triphosphate / Q000494:pharmacology; D027322:Amino Acid Transport System X-AG / Q000502:physiology*; D000818:Animals; D002264:Carboxylic Acids / Q000494:pharmacology; D004347:Drug Interactions; D004558:Electric Stimulation; D018683:Excitatory Amino Acid Agents / Q000494:pharmacology; D066298:In Vitro Techniques; D008274:Magnesium / Q000378:metabolism; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D008954:Models, Biological; D018408:Patch-Clamp Techniques / Q000379:methods; D017397:Prefrontal Cortex / Q000166:cytology*; D017966:Pyramidal Cells / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D018094:Receptors, Metabotropic Glutamate / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000502:physiology*
D027322:Amino Acid Transport System X-AG; D002264:Carboxylic Acids; D018683:Excitatory Amino Acid Agents; D011725:Pyridines; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; C108822:metabotropic glutamate receptor 2; C521977:poly-2,6-pyridinedicarboxylic acid; D000255:Adenosine Triphosphate; D008274:Magnesium