Modulation of ionotropic GABA receptors by 6-methoxyflavanone and 6-methoxyflavone.
We evaluated the effects of 6-methoxyflavanone and 6-methoxyflavone on wild-type α1/α2β2γ2L GABAA and ρ1 GABAC receptors and on mutant ρ1I307S, ρ1W328 M, ρ1I307S/W328 M GABAC receptors expressed in Xenopus oocytes using two-electrode voltage clamp and radioligand binding. 6-Methoxyflavanone and 6-methoxyflavone act as a flumazenil-insensitive positive allosteric modulator of GABA responses at human recombinant α1β2γ2L and α2β2γ2L GABAA receptors. However, unlike 6-methoxyflavone, 6-methoxyflavanone was relatively inactive at α1β2 GABAA receptors. 6-Methoxyflavanone inhibited [(3)H]-flunitrazepam binding to rat brain membranes. Both flavonoids were found to be inactive as modulators at ρ1, ρ1I307S and ρ1W328 M GABA receptors but acted as positive allosteric modulators of GABA at the benzodiazepine sensitive ρ1I307S/W328 M GABA receptors. This double mutant retains ρ1 properties of being insensitive to bicuculline and antagonised by TPMPA and THIP. Additionally, 6-methoxyflavanone was also a partial agonist at ρ1W328 M GABA receptors. The relative inactivity of 6-methoxyflavanone at α1β2 GABAA receptors and it's partial agonist action at ρ1W328 M GABA receptors suggest that it exhibits a unique profile not matched by other flavonoids.
Department of Pharmacology, The University of Sydney, Sydney, NSW, 2006, Australia.
Belinda J
BJ
Hall
Nasiara
N
Karim
Mary
M
Chebib
Graham A R
GA
Johnston
Jane R
JR
Hanrahan
D000494:Allosteric Regulation; D000818:Animals; D044950:Flavanones / Q000494:pharmacology*; D047309:Flavones / Q000494:pharmacology*; D018079:Receptors, GABA / Q000187:drug effects* / Q000378:metabolism; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D014982:Xenopus laevis
C000598908:6-methoxyflavanone; C000593132:6-methoxyflavone; D044950:Flavanones; D047309:Flavones; D018079:Receptors, GABA; D011994:Recombinant Proteins