Altered receptor subtypes in the forebrain of GABA(A) receptor delta subunit-deficient mice: recruitment of gamma 2 subunits.
A GABA(A) receptor delta subunit-deficient mouse line was created by homologous recombination in embryonic stem cells to investigate the role of the subunit in the brain GABA(A) receptors. High-affinity [(3)H]muscimol binding to GABA sites as studied by ligand autoradiography was reduced in various brain regions of delta(-/-) animals. [(3)H]Ro 15-4513 binding to benzodiazepine sites was increased in delta(-/-) animals, partly due to an increment of diazepam-insensitive receptors, indicating an augmented forebrain assembly of gamma 2 subunits with alpha 4 subunits. In the western blots of forebrain membranes of delta(-/-) animals, the level of gamma 2 subunit was increased and that of alpha 4 decreased, while the level of alpha1 subunits remained unchanged. In the delta(-/-) forebrains, the remaining alpha 4 subunits were associated more often with gamma 2 subunits, since there was an increase in the alpha 4 subunit level immunoprecipitated by the gamma 2 subunit antibody. The pharmacological properties of t-butylbicyclophosphoro[(35)S]thionate binding to the integral ion-channel sites were slightly altered in the forebrain and cerebellum, consistent with elevated levels of alpha 4 gamma 2 and alpha 6 gamma 2 subunit-containing receptors, respectively.The altered pharmacology of forebrain GABA(A) receptors and the decrease of the alpha 4 subunit level in delta subunit-deficient mice suggest that the delta subunit preferentially assembles with the alpha 4 subunit. The delta subunit seems to interfere with the co-assembly of alpha 4 and gamma 2 subunits and, therefore, in its absence, the gamma 2 subunit is recruited into a larger population of alpha 4 subunit-containing functional receptors. These results support the idea of subunit competition during the assembly of native GABA(A) receptors.
Korpi
E R
ER
Department of Pharmacology and Clinical Pharmacology, University of Turku, Finland. esa.korpi@utu.fi
Mihalek
R M
RM
Sinkkonen
S T
ST
Hauer
B
B
Hevers
W
W
Homanics
G E
GE
Sieghart
W
W
Lüddens
H
H
D000345:Affinity Labels; D000818:Animals; D001386:Azides; D001569:Benzodiazepines / Q000819:agonists; D001665:Binding Sites / Q000187:drug effects / Q000502:physiology; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D005260:Female; D018755:GABA Agonists; D007473:Ion Channels / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D018345:Mice, Knockout; D009118:Muscimol; D009154:Mutation / Q000235:genetics; D009433:Neural Inhibition / Q000187:drug effects / Q000502:physiology*; D009474:Neurons / Q000187:drug effects / Q000378:metabolism*; D011869:Radioligand Assay; D011963:Receptors, GABA-A / Q000172:deficiency* / Q000187:drug effects / Q000235:genetics; D009435:Synaptic Transmission / Q000187:drug effects / Q000502:physiology*; D014316:Tritium; D005680:gamma-Aminobutyric Acid / Q000378:metabolism* / Q000494:pharmacology
D000345:Affinity Labels; D001386:Azides; D018755:GABA Agonists; D007473:Ion Channels; D011963:Receptors, GABA-A; D014316:Tritium; D001569:Benzodiazepines; D009118:Muscimol; D005680:gamma-Aminobutyric Acid; C042957:Ro 15-4513