NMDA-mediated modulation of gamma-aminobutyric acid type A receptor function in cerebellar granule neurons.
GABAA receptors are ligand-gated CI- ion channels with multiple clinically relevant drug-recognition sites. We have previously shown that stimulation of N-methyl-D-aspartic acid (NMDA)-specific glutamate receptors quantitatively alters selected GABAA receptor subunit mRNAs and proteins in primary cultures of rat cerebellar granule neurons. We used whole-cell recordings of GABA-elicited CI- currents and flunitrazepam binding experiments in granule cell cultures maintained in low K+ (12.5 mM), cells maintained in low K+ and treated with a single dose of NMDA (10 microM), and cell cultures maintained in depolarizing concentrations of K+ (25 mM). The EC50 obtained from the dose-response curves for GABA in eliciting a maximal response was comparable in neurons maintained in high K+ or in low K+ and treated with a single dose of NMDA, but that it increased significantly in cells maintained in low K+. The potentiation of GABA-gated CI- currents by flunitrazepam increased significantly, while the negative allosteric modulator methyl-6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM) was significantly more effective in cultures either maintained in high K+ or treated with NMDA. This was coincident with a twofold increase in the Bmax associated with flunitrazepam binding. To further characterize the receptor assemblies present in the depolarization and NMDA induced paradigms, the Zn(2+)-induced inhibition of GABA-gated CI- currents was reduced as was the inhibition mediated by furosemide. Our data indicate that GABAA receptor assemblies alter their composition in response to excitatory afferent receptor stimulation.
D000818:Animals; D002478:Cells, Cultured; D002531:Cerebellum / Q000166:cytology / Q000378:metabolism*; D002712:Chlorides / Q000502:physiology; D005445:Flunitrazepam / Q000378:metabolism; D005665:Furosemide / Q000494:pharmacology; D015640:Ion Channel Gating; D016202:N-Methylaspartate / Q000494:pharmacology*; D009474:Neurons / Q000378:metabolism*; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000494:pharmacology; D011189:Potassium Chloride / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism*; D015032:Zinc / Q000494:pharmacology; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
D002712:Chlorides; D011963:Receptors, GABA-A; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; D016202:N-Methylaspartate; D011189:Potassium Chloride; D005665:Furosemide; D015032:Zinc; D011188:Potassium