In vitro evidence that 5-hydroxytryptamine increases efflux of glial glutamate via 5-HT(2A) receptor activation.
Recent studies have established the presence of 5-hydroxytryptamine (5-HT)(2A) receptors on glial cells in culture and in the brain in situ. Here we used cultured C6 glioma cells to investigate the possibility that 5-HT(2A) receptors on glia regulate glutamate release from the cell. The efflux of endogenous glutamate from cultured C6 glioma cells was increased by addition of 5-HT in a concentration-dependent manner (maximal effect +200%). The efflux of serine and aspartate was not altered. The effect of 5-HT was mimicked by both the nonselective 5-HT receptor agonist quipazine and the selective 5-HT(2) receptor agonist 4-iodo-2,5-dimethoxyamphetamine (DOI; both 0.01-100 microM). The 5-HT(2A) receptor antagonists ketanserin (1 microM) and spiperone (1 microM) inhibited the glutamate response to 5-HT, quipazine, and DOI, whereas the effect of 5-HT was not inhibited by the 5-HT(2B/C) receptor antagonist SB200646 (1 microM). The effect of 5-HT on glutamate was specific in that it was reduced in low-calcium medium but was not prevented by furosemide (5 mM), which prevents cell swelling-induced glutamate release. Finally, the glutamate uptake inhibitor 2,4,trans-pyrollidine dicarboxylic acid (50 microM) did not block the 5-HT-induced efflux of glutamate, making involvement of glutamate transport unlikely. In conclusion, 5-HT stimulates the efflux of glutamate from C6 glioma cells following 5-HT(2A) receptor activation and involves a calcium-dependent mechanism.
Meller
R
R
University Department of Clinical Pharmacology, Radcliffe Infirmary, Oxford, United Kingdom. rmeller@downeurobiology.org
Harrison
P J
PJ
Elliott
J M
JM
Sharp
T
T
D000818:Animals; D003994:Bucladesine / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002851:Chromatography, High Pressure Liquid; D017077:Culture Media, Conditioned / Q000737:chemistry / Q000378:metabolism; D003998:Dicarboxylic Acids / Q000494:pharmacology; D004232:Diuretics / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D005665:Furosemide / Q000494:pharmacology; D018698:Glutamic Acid / Q000378:metabolism*; D009457:Neuroglia / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D014179:Neurotransmitter Uptake Inhibitors / Q000494:pharmacology; D011759:Pyrrolidines / Q000494:pharmacology; D051381:Rats; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin / Q000187:drug effects / Q000378:metabolism*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology
D017077:Culture Media, Conditioned; D003998:Dicarboxylic Acids; D004232:Diuretics; D014179:Neurotransmitter Uptake Inhibitors; D011759:Pyrrolidines; D044402:Receptor, Serotonin, 5-HT2A; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D012701:Serotonin; D018698:Glutamic Acid; D003994:Bucladesine; D005665:Furosemide; C083486:pyrrolidine-2,4-dicarboxylic acid; D002118:Calcium