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Modulation of extracellular glutamate concentration in rat brain slices by cystine‐glutamate exchange

Modulation of extracellular glutamate concentration in rat brain slices by cystine‐glutamate... 1 The role of cystine‐glutamate exchange in controlling the extracellular glutamate concentration in the central nervous system was examined by whole‐cell clamping neurons in rat brain slices, and using their glutamate receptors as sensors of extracellular glutamate concentration. 2 Applying cystine to cerebellar slices generated a membrane current in Purkinje cells which was abolished by glutamate receptor blockers. Similar cystine‐evoked currents were seen in pyramidal cells of frontal cortex slices. 3 Control experiments on non‐N‐methyl‐D‐aspartate (non‐NMDA) receptors in enzymatically isolated Purkinje cells showed that cystine did not produce a current in slice Purkinje cells by directly activating glutamate receptors, nor by potentiating the action of background levels of glutamate on receptors. Experiments on isolated salamander Müller cells showed that cystine did not block Na+‐dependent GLAST glutamate transporters (homologous to the transporters in the Bergmann glia ensheathing the Purkinje cells), nor did it block the current produced by EAAT4 and EAAC1 glutamate transporters in Purkinje cells. Thus the cystine‐evoked current in Purkinje cells is not due to a rise in extracellular glutamate concentration caused by block of Na+‐dependent uptake. 4 The dependence of cystine‐evoked current on cystine concentration in slice Purkinje cells could be fitted by a Michaelis‐Menten relation with a Km of 250 μM. The Km predicted from this for cystine activating glutamate efflux is less than 140 μM, because of the non‐linear dependence on glutamate concentration of the Purkinje cell current. The current evoked by 1 mM cystine was little affected by removal of extracellular chloride or addition of 1 mM furosemide (frusemide), but was potentiated by 1 mM 4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid (DIDS). 5 These data suggest that external cystine generates a current in slice Purkinje cells by activating cystine‐glutamate exchange in cells of the slice, releasing glutamate which activates non‐NMDA receptors in the Purkinje cell membrane. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Physiology Wiley

Modulation of extracellular glutamate concentration in rat brain slices by cystine‐glutamate exchange

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References (53)

Publisher
Wiley
Copyright
Copyright © 1999 Wiley Subscription Services, Inc., A Wiley Company
ISSN
0022-3751
eISSN
1469-7793
DOI
10.1111/j.1469-7793.1999.783ad.x
Publisher site
See Article on Publisher Site

Abstract

1 The role of cystine‐glutamate exchange in controlling the extracellular glutamate concentration in the central nervous system was examined by whole‐cell clamping neurons in rat brain slices, and using their glutamate receptors as sensors of extracellular glutamate concentration. 2 Applying cystine to cerebellar slices generated a membrane current in Purkinje cells which was abolished by glutamate receptor blockers. Similar cystine‐evoked currents were seen in pyramidal cells of frontal cortex slices. 3 Control experiments on non‐N‐methyl‐D‐aspartate (non‐NMDA) receptors in enzymatically isolated Purkinje cells showed that cystine did not produce a current in slice Purkinje cells by directly activating glutamate receptors, nor by potentiating the action of background levels of glutamate on receptors. Experiments on isolated salamander Müller cells showed that cystine did not block Na+‐dependent GLAST glutamate transporters (homologous to the transporters in the Bergmann glia ensheathing the Purkinje cells), nor did it block the current produced by EAAT4 and EAAC1 glutamate transporters in Purkinje cells. Thus the cystine‐evoked current in Purkinje cells is not due to a rise in extracellular glutamate concentration caused by block of Na+‐dependent uptake. 4 The dependence of cystine‐evoked current on cystine concentration in slice Purkinje cells could be fitted by a Michaelis‐Menten relation with a Km of 250 μM. The Km predicted from this for cystine activating glutamate efflux is less than 140 μM, because of the non‐linear dependence on glutamate concentration of the Purkinje cell current. The current evoked by 1 mM cystine was little affected by removal of extracellular chloride or addition of 1 mM furosemide (frusemide), but was potentiated by 1 mM 4,4′‐diisothiocyanatostilbene‐2,2′‐disulfonic acid (DIDS). 5 These data suggest that external cystine generates a current in slice Purkinje cells by activating cystine‐glutamate exchange in cells of the slice, releasing glutamate which activates non‐NMDA receptors in the Purkinje cell membrane.

Journal

The Journal of Physiology – Wiley

Published: Feb 1, 1999

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