Glutamate stimulates ascorbate transport by astrocytes.
The concentrations of glutamate and ascorbate in brain extracellular fluid increase following seizure activity, trauma and ischemia. Extracellular ascorbate concentration also rises following intracerebral glutamate injection. We hypothesized that glutamate triggers the release of ascorbate from astrocytes. We observed in primary cultures of rat cerebral astrocytes that glutamate increased ascorbate efflux significantly within 30 min. The half-maximal effective concentration of glutamate was 180+/-30 microM. Glutamate-stimulated efflux of ascorbate was attenuated by hypertonic media. 4,4'-diisothiocyanatostilbene-2,2'-disulfonic acid inhibited both Na(+)-dependent glutamate uptake and ascorbate efflux. Two other inhibitors of volume-sensitive organic anion channels (1, 9-dideoxyforskolin and 5-nitro-2-(3-phenylpropylamino) benzoic acid) did not slow glutamate uptake but prevented stimulation of ascorbate efflux. Glutamate also stimulated the uptake of ascorbate by ascorbate-depleted astrocytes. In contrast, glutamate uptake was not affected by intracellular ascorbate, thus ruling out a putative glutamate-ascorbate heteroexchange mechanism. These results are consistent with activation by glutamate of ascorbate-permeant channels in astrocytes.
Wilson
J X
JX
Department of Physiology, Faculty of Medicine, The University of Western Ontario, Medical Science Bldg, London, Ontario, Canada. jwilson@physiology.uwo.ca
Peters
C E
CE
Sitar
S M
SM
Daoust
P
P
Gelb
A W
AW
D000596:Amino Acids / Q000378:metabolism; D000818:Animals; D027321:Anion Transport Proteins; D001205:Ascorbic Acid / Q000378:metabolism* / Q000493:pharmacokinetics; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*; D001692:Biological Transport / Q000187:drug effects / Q000502:physiology; D002352:Carrier Proteins / Q000037:antagonists & inhibitors; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D004305:Dose-Response Relationship, Drug; D005110:Extracellular Space / Q000378:metabolism; D018698:Glutamic Acid / Q000378:metabolism* / Q000493:pharmacokinetics / Q000494:pharmacology; D007424:Intracellular Fluid / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D012462:Saline Solution, Hypertonic / Q000494:pharmacology
D000596:Amino Acids; D027321:Anion Transport Proteins; D002352:Carrier Proteins; D012462:Saline Solution, Hypertonic; D018698:Glutamic Acid; D001205:Ascorbic Acid