Metabotropic Glutamate Receptor in C6BU-1 Glioma Cell Has NMDA Receptor-Ion Channel Complex-Like Properties and Interacts with Serotonin2 Receptor-Stimulated Signal Transduction |
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Authors: | †Hideto Shinno Masahiko Mikuni Kazuko Saitoh Urara Tomita †Shigeto Yamawaki Kiyohisa Takahashi |
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Institution: | Department of Mental Disorder Research, National Institute of Neuroscience, National Center of Neurology and Psychiatry, Tokyo;and; Department of Psychiatry and Neurosciences, Hiroshima University School of Medicine, Hiroshima, Japan |
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Abstract: | Abstract: We found in cultured glioma (C6BU-1) cells that excitatory amino acids (EAAs) such as glutamate, N-methyl-d -aspartate (NMDA), aspartate, and metabotropic glutamate receptor agonist trans-(±)-1-amino-1,3-cyclopentanedicarboxylate caused an increase in the inositol 1,4,5-trisphosphate formation and the intracellular Ca2+ concentration (Ca2+]i) in the absence of extracellular Mg2+ and Ca2+. Pertussis toxin treatment abolished this glutamate-induced Ca2+]i increase. Various antagonists against NMDA receptor-ion channel complex, such as Mg2+, d -2-amino-5-phosphonovalerate (d -APV), HA-966, and MK-801, also inhibited the increase in Ca2+]i induced by glutamate. These results indicate that these metabotropic EAA receptors coupled to pertussis toxin-susceptible GTP-binding protein and phospholipase C system in C6BU-1 glioma cells have the pharmacological properties of NMDA receptor-ion channel complexes. We also found that in the presence of Mg2+ these metabotropic receptors resemble the NMDA receptor-ion channel complex interacted with 5-hydroxytryptamine2 (5-HT2) receptor signaling. EAAs inhibited 5-HT2 receptor-mediated intracellular Ca2+ mobilization and inositol 1,4,5-trisphosphate formation in a concentration-dependent manner. The inhibitory effect of glutamate was reversed by various NMDA receptor antagonists (d -APV, MK-801, phencyclidine, and HA-966), but l -APV failed to block the inhibitory effect of glutamate. The same result was observed in the absence of extracellular Ca2+. In addition, this inhibitory effect on 5-HT2 receptor-mediated signal transduction was abolished by treatment of C6BU-1 cells with pertussis toxin, whereas 5-HT2 receptor-mediated Ca2+]i increase was not abolished by pertussis toxin treatment. We can, therefore, conclude that the inhibitory effect of glutamate is not a result of the influx of Ca2+ through the ion channel and that it operates via metabotropic glutamate receptors, having NMDA receptor-ion channel complex-like properties and being coupled with pertussis toxin-sensitive GTP-binding protein and phospholipase C. |
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Keywords: | N-Methyl-d-aspartate Metabotropic glutamate receptor C6BU-1 glioma cell 5-Hydroxytryptamine2 receptor Inositol 1 4 5 - trisphosphate Pertussis toxin |
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