title: Altered kinetics and benzodiazepine sensitivity of a GABAA receptor subunit mutation [gamma 2(R43Q)] found in human epilepsy.
abstract: The gamma-aminobutyric acid type A (GABA(A)) receptor mediates fast inhibitory synaptic transmission in the CNS. Dysfunction of the GABA(A) receptor would be expected to cause neuronal hyperexcitability, a phenomenon linked with epileptogenesis. We have investigated the functional consequences of an arginine-to-glutamine mutation at position 43 within the GABA(A) gamma(2)-subunit found in a family with childhood absence epilepsy and febrile seizures. Rapid-application experiments performed on receptors expressed in HEK-293 cells demonstrated that the mutation slows GABA(A) receptor deactivation and increases the rate of desensitization, resulting in an accumulation of desensitized receptors during repeated, short applications. In Xenopus laevis oocytes, two-electrode voltage-clamp analysis of steady-state currents obtained from alpha(1)beta(2)gamma(2) or alpha(1)beta(2)gamma(2)(R43Q) receptors did not reveal any differences in GABA sensitivity. However, differences in the benzodiazepine pharmacology of mutant receptors were apparent. Mutant receptors expressed in oocytes displayed reduced sensitivity to diazepam and flunitrazepam but not the imidazopyridine zolpidem. These results provide evidence of impaired GABA(A) receptor function that could decrease the efficacy of transmission at inhibitory synapses, possibly generating a hyperexcitable neuronal state in thalamocortical networks of epileptic patients possessing the mutant subunit.
authors.affiliation: Department of Physiology, University of Melbourne, Victoria 3010, Australia.
authors.forename: David N
authors.initials: DN
authors.lastname: Bowser
authors.forename: David A
authors.initials: DA
authors.lastname: Wagner
authors.forename: Cynthia
authors.initials: C
authors.lastname: Czajkowski
authors.forename: Brett A
authors.initials: BA
authors.lastname: Cromer
authors.forename: Michael W
authors.initials: MW
authors.lastname: Parker
authors.forename: Robyn H
authors.initials: RH
authors.lastname: Wallace
authors.forename: Louise A
authors.initials: LA
authors.lastname: Harkin
authors.forename: John C
authors.initials: JC
authors.lastname: Mulley
authors.forename: Carla
authors.initials: C
authors.lastname: Marini
authors.forename: Samuel F
authors.initials: SF
authors.lastname: Berkovic
authors.forename: David A
authors.initials: DA
authors.lastname: Williams
authors.forename: Mathew V
authors.initials: MV
authors.lastname: Jones
authors.forename: Steven
authors.initials: S
authors.lastname: Petrou
mesh_terms: D019943:Amino Acid Substitution; D000818:Animals; D014151:Anti-Anxiety Agents / Q000494:pharmacology*; D002460:Cell Line; D003975:Diazepam / Q000494:pharmacology; D004827:Epilepsy / Q000235:genetics* / Q000503:physiopathology; D005445:Flunitrazepam / Q000494:pharmacology; D006801:Humans; D007700:Kinetics; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D016297:Mutagenesis, Site-Directed; D009474:Neurons / Q000502:physiology; D009865:Oocytes / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques; D021122:Protein Subunits / Q000235:genetics; D011725:Pyridines / Q000494:pharmacology; D011963:Receptors, GABA-A / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000378:metabolism; D013569:Synapses / Q000502:physiology; D009435:Synaptic Transmission; D014162:Transfection; D014981:Xenopus; D000077334:Zolpidem; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology
chemical_list: D014151:Anti-Anxiety Agents; D021122:Protein Subunits; D011725:Pyridines; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D005680:gamma-Aminobutyric Acid; D005445:Flunitrazepam; D000077334:Zolpidem; D003975:Diazepam