Citrate modulates the regulation by Zn2+ of N-methyl-D-aspartate receptor-mediated channel current and neurotransmitter release.
The effect of the two metal-ion chelators EDTA and citrate on the action of N-methyl-D-aspartate (NMDA) receptors was investigated by use of cultured mouse cerebellar granule neurons and Xenopus oocytes, respectively, to monitor either NMDA-evoked transmitter release or membrane currents. Transmitter release from the glutamatergic neurons was determined by superfusion of the cells after preloading with the glutamate analogue D-[3H]aspartate. The oocytes were injected with mRNA isolated from mouse cerebellum and, after incubation to allow translation to occur, currents mediated by NMDA were recorded electrophysiologically by voltage clamp at a holding potential of -80 mV. It was found that citrate as well as EDTA could attenuate the inhibitory action of Zn2+ on NMDA receptor-mediated transmitter release from the neurons and membrane currents in the oocytes. These effects were specifically related to the NMDA receptor, since the NMDA receptor antagonist MK-801 abolished the action and no effects of Zn2+ and its chelators were observed when kainate was used to selectively activate non-NMDA receptors. Since it was additionally demonstrated that citrate (and EDTA) preferentially chelated Zn2+ rather than Ca2+, the present findings strongly suggest that endogenous citrate released specifically from astrocytes into the extracellular space in the brain may function as a modulator of NMDA receptor activity. This is yet another example of astrocytic influence on neuronal activity.
Westergaard
N
N
Department of Biological Sciences, Royal Danish School of Pharmacy, Copenhagen.
Banke
T
T
Wahl
P
P
Sonnewald
U
U
Schousboe
A
A
D000818:Animals; D001253:Astrocytes / Q000502:physiology; D002531:Cerebellum / Q000166:cytology / Q000502:physiology; D002951:Citrates / Q000494:pharmacology*; D019343:Citric Acid; D004305:Dose-Response Relationship, Drug; D004492:Edetic Acid / Q000494:pharmacology; D004553:Electric Conductivity; D007473:Ion Channels / Q000187:drug effects*; D007608:Kainic Acid / Q000494:pharmacology; D051379:Mice; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects*; D014981:Xenopus; D015032:Zinc / Q000494:pharmacology*
D002951:Citrates; D007473:Ion Channels; D016194:Receptors, N-Methyl-D-Aspartate; D019343:Citric Acid; D004492:Edetic Acid; D015032:Zinc; D007608:Kainic Acid