Metabotropic glutamate receptor in C6BU-1 glioma cell has NMDA receptor-ion channel complex-like properties and interacts with serotonin2 receptor-stimulated signal transduction.
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.
Shinno
H
H
Department of Mental Disorder Research, National Institute of Neuroscience, Tokyo, Japan.
Mikuni
M
M
Saitoh
K
K
Tomita
U
U
Yamawaki
S
S
Takahashi
K
K
D015763:2-Amino-5-phosphonovalerate / Q000494:pharmacology; D000818:Animals; D001224:Aspartic Acid / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism* / Q000494:pharmacology; D002460:Cell Line; D003515:Cycloleucine / Q000031:analogs & derivatives / Q000494:pharmacology; D016291:Dizocilpine Maleate / Q000494:pharmacology; D005910:Glioma; D018698:Glutamic Acid / Q000494:pharmacology; D015544:Inositol 1,4,5-Trisphosphate / Q000378:metabolism*; D007473:Ion Channels / Q000378:metabolism*; D007608:Kainic Acid / Q000494:pharmacology; D007700:Kinetics; D015636:Magnesium Chloride / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D009498:Neurotoxins / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D051381:Rats; D018094:Receptors, Metabotropic Glutamate / Q000378:metabolism*; D016194:Receptors, N-Methyl-D-Aspartate / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000502:physiology*; D015398:Signal Transduction; D014407:Tumor Cells, Cultured
D007473:Ion Channels; D009498:Neurotoxins; D011760:Pyrrolidinones; D018094:Receptors, Metabotropic Glutamate; D016194:Receptors, N-Methyl-D-Aspartate; D011985:Receptors, Serotonin; D015636:Magnesium Chloride; D003515:Cycloleucine; C036361:1-amino-1,3-dicarboxycyclopentane; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D016291:Dizocilpine Maleate; D015763:2-Amino-5-phosphonovalerate; D015544:Inositol 1,4,5-Trisphosphate; C001369:1-hydroxy-3-amino-2-pyrrolidone; D007608:Kainic Acid; D002118:Calcium