Enhanced ethanol inhibition of recombinant N-methyl-D-aspartate receptors by magnesium: role of NR3A subunits.
BACKGROUND
The effects of ethanol on brain function are thought to be partly because of altered activity of ion channels that regulate synaptic activity. Results from previous studies from this lab and others have shown that ethanol inhibits the function of the N-methyl-D-aspartate (NMDA) receptors, a calcium-permeable ion channel activated by the neurotransmitter glutamate. Factors that influence the acute sensitivity of NMDA receptors to ethanol may be critical in determining how neurons and neuronal networks respond to the presence of ethanol. In this study, we have examined the effect of physiologically relevant concentrations of magnesium on the ethanol sensitivity of recombinant NMDA receptors and how ethanol inhibition under these conditions is influenced by the NR3A subunit.


METHODS
Recombinant cDNAs encoding NMDA receptor subunits were expressed in human embryonic kidney 293 cells. Whole-cell patch-clamp electrophysiology was used to measure currents induced by rapid application of glutamate in the absence and presence of ethanol.


RESULTS
In magnesium-free recording solution, ethanol inhibited glutamate-mediated currents in cells transfected with NMDA receptor subunits. The magnitude of ethanol inhibition was significantly enhanced when recordings were carried out in media containing 1 mM magnesium. This effect was reversible and required magnesium-sensitive receptors. Magnesium did not enhance ethanol inhibition of glycine-activated NR1/NR3A/NR3B receptors. However, NR3A co-expression prevented the enhancement of ethanol's inhibitory effect on receptors composed of NR2A but not NR2B subunits.


CONCLUSIONS
These results suggest that under physiological conditions, NR3A may be an important regulator of the acute ethanol sensitivity of brain NMDA receptors.
Jin
Chun
C
Department of Neurosciences and Center for Drug and Alcohol Programs, Medical University of South Carolina, Charleston, South Carolina.
Smothers
C Thetford
CT
Woodward
John J
JJ
D002460:Cell Line; D018076:DNA, Complementary / Q000235:genetics; D004553:Electric Conductivity; D000431:Ethanol / Q000494:pharmacology*; D015870:Gene Expression; D018698:Glutamic Acid / Q000494:pharmacology; D005998:Glycine / Q000494:pharmacology; D006801:Humans; D007668:Kidney / Q000196:embryology; D008274:Magnesium / Q000494:pharmacology*; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000502:physiology; D016194:Receptors, N-Methyl-D-Aspartate / Q000037:antagonists & inhibitors* / Q000187:drug effects / Q000235:genetics / Q000502:physiology; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors* / Q000235:genetics; D014162:Transfection
D018076:DNA, Complementary; C464437:NR3A NMDA receptor; D021122:Protein Subunits; D016194:Receptors, N-Methyl-D-Aspartate; D011994:Recombinant Proteins; D000431:Ethanol; D018698:Glutamic Acid; D008274:Magnesium; D005998:Glycine