title: A dual mechanism for impairment of GABAA receptor activity by NMDA receptor activation in rat cerebellum granule cells.
abstract: The function of the GABAA receptor has been studied using the whole cell voltage clamp recording technique in rat cerebellum granule cells in culture. Activation of NMDA-type glutamate receptors causes a reduction in the effect of GABA. Full GABAA receptor activity was recovered after washing out NMDA and NMDA action was prevented in a Mg+2 containing medium. The NMDA effect was also absent when extracellular Ca+2 was replaced by Ba+2 and when 10 mM Bapta was present in the intracellular solution. Charge accumulations via voltage activated Ca+2 channels greater than the ones via NMDA receptors do not cause any reduction in GABAA receptor function, suggesting that Ca+2 influx through NMDA receptor channels is critical for the effect. The NMDA effect was reduced by including adenosine-5'-O-3-thiophosphate (ATP-gamma-S) in the internal solution and there was a reduction in the NMDA effect caused by deltamethrin, a calcineurin inhibitor. Part of the NMDA induced GABAA receptor impairment was prevented by prior treatment with L-arginine. Analogously, part of the NMDA effect was prevented by blockage of NO-synthase activity by N omega-nitro-L-arginine. A combination of NO-synthase and calcineurin inhibitors completely eliminated the NMDA action. An analogous result was obtained by combining the NO-synthase inhibitor with the addition of ATP-gamma-S to the pipette medium. The additivity of the prevention of the NMDA impairment of GABAA receptor by blocking the L-arginine/NO pathway and inhibiting calcineurin activity suggests an independent involvement of these two pathways in the interaction between NMDA and the GABAA receptor. On the one hand Ca+2 influx across NMDA channels activates calcineurin and dephosphorylates the GABAA receptor complex directly or dephosphorylates proteins critical for the function of the receptor. On the other hand, Ca+2 influx activates NO-synthase and induces nitric oxide production, which regulates such receptors via protein kinase G activity.
authors.affiliation: INFM Unità di Genova, Dipartimento di Fisica, Università di Genova, Italy.
authors.forename: M
authors.initials: M
authors.lastname: Robello
authors.forename: C
authors.initials: C
authors.lastname: Amico
authors.forename: A
authors.initials: A
authors.lastname: Cupello
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D019703:Calcineurin; D002118:Calcium / Q000378:metabolism; D002148:Calmodulin-Binding Proteins / Q000037:antagonists & inhibitors / Q000494:pharmacology; D002478:Cells, Cultured; D002531:Cerebellum / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure*; D003594:Cytoplasmic Granules / Q000187:drug effects / Q000502:physiology / Q000648:ultrastructure; D004594:Electrophysiology; D004791:Enzyme Inhibitors / Q000494:pharmacology; D016202:N-Methylaspartate / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000037:antagonists & inhibitors; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors / Q000494:pharmacology; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects / Q000502:physiology*; D016194:Receptors, N-Methyl-D-Aspartate / Q000187:drug effects / Q000502:physiology*
chemical_list: D002148:Calmodulin-Binding Proteins; D004791:Enzyme Inhibitors; D011963:Receptors, GABA-A; D016194:Receptors, N-Methyl-D-Aspartate; D016202:N-Methylaspartate; D001120:Arginine; D019001:Nitric Oxide Synthase; D019703:Calcineurin; D010749:Phosphoprotein Phosphatases; D002118:Calcium