Current potentiation by diazepam but not GABA sensitivity is determined by a single histidine residue.
The GABAA/benzodiazepine receptor is the principal inhibitory neurotransmitter receptor in the mammalian brain and is assembled from sequence-related subunits, such as alpha 1 beta 2 gamma 2. In contrast to alpha 1 beta 2 gamma 2 receptors, alpha 6 beta 2 gamma 2 receptors fail to exhibit high-affinity binding of allosteric positive modulators of GABA-activated chloride currents. The critical determinant responsible for this difference in ligand binding was previously traced to a position in the extracellular domain of the two alpha subunits (alpha 1 His100 and alpha 6 Arg 101). We now show by patch clamp analysis that this amino acid exchange also determines the diazepam potentiation. Thus, alpha 1(Arg101)beta 2 gamma 2 receptors do not, but alpha 6(His100)beta 2 gamma 2 receptors do exhibit diazepam potentiation. However, the same extracellular determinant is not responsible for the increased GABA sensitivity of alpha 6 beta 2 gamma 2 receptors relative to alpha 1 beta 2 gamma 2 receptors as revealed by electrophysiological analysis and by differential GABA sensitivity of [35S]TBPS binding.
Department of Neurobiology, University of Heidelberg, Germany.
C
C
Kleingoor
H A
HA
Wieland
E R
ER
Korpi
P H
PH
Seeburg
H
H
Kettenmann
D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D003975:Diazepam / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005071:Evoked Potentials / Q000187:drug effects; D006639:Histidine; D006801:Humans; D007668:Kidney; D046911:Macromolecular Substances; D008564:Membrane Potentials / Q000187:drug effects; D016296:Mutagenesis; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects / Q000235:genetics / Q000502:physiology*; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D005680:gamma-Aminobutyric Acid / Q000494:pharmacology*
D046911:Macromolecular Substances; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D006639:Histidine; D005680:gamma-Aminobutyric Acid; D003975:Diazepam