Slow actions of neuroactive steroids at GABAA receptors.
Neuroactive steroids are potent and efficacious modulators of GABA(A) receptor activity and are potent sedatives and anesthetics. These positive modulators of GABA(A) receptors both potentiate the actions of GABA at the receptor and, at higher concentrations, directly gate the channel. The contribution of direct gating to the cellular and behavioral effects of neuroactive steroids is considered of little significance because it has been generally found that concentrations well above those needed for anesthesia are required to gate channels. By studying solitary glutamatergic neurons devoid of synaptic GABA input, we show that direct gating occurs and significantly alters membrane excitability at concentrations < or =100 nm. We propose that the relevance of direct gating has been overlooked partly because of the extremely slow kinetics of receptor activation and deactivation. We show that slow deactivation of directly gated currents does not result from an inherently tight ligand-receptor interaction because the slow deactivation is markedly accelerated by gamma-cyclodextrin application. We hypothesize that steroids access the relevant GABA(A) receptor site from a non-aqueous reservoir, likely the plasma membrane, and that it is slow reservoir accumulation and departure that accounts for the slow kinetics of receptor gating by neuroactive steroids.
Shu
Hong-Jin
HJ
Department of Psychiatry, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Eisenman
Lawrence N
LN
Jinadasa
Deepani
D
Covey
Douglas F
DF
Zorumski
Charles F
CF
Mennerick
Steven
S
D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000502:physiology*; D002478:Cells, Cultured / Q000187:drug effects; D002712:Chlorides / Q000378:metabolism*; D018755:GABA Agonists / Q000494:pharmacology; D018756:GABA Antagonists / Q000494:pharmacology; D006624:Hippocampus / Q000166:cytology; D015640:Ion Channel Gating / Q000187:drug effects* / Q000502:physiology; D017136:Ion Transport / Q000187:drug effects / Q000502:physiology; D007700:Kinetics; D008024:Ligands; D009474:Neurons / Q000187:drug effects; D009865:Oocytes; D018408:Patch-Clamp Techniques; D011280:Pregnanolone / Q000494:pharmacology*; D011485:Protein Binding; D011724:Pyridazines / Q000494:pharmacology; D011810:Quinoxalines / Q000494:pharmacology; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D011963:Receptors, GABA-A / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D011994:Recombinant Proteins / Q000187:drug effects / Q000378:metabolism; D014162:Transfection; D014981:Xenopus; D047408:gamma-Cyclodextrins / Q000494:pharmacology
D002712:Chlorides; D018755:GABA Agonists; D018756:GABA Antagonists; D008024:Ligands; D011724:Pyridazines; D011810:Quinoxalines; D012333:RNA, Messenger; D011963:Receptors, GABA-A; D011994:Recombinant Proteins; D047408:gamma-Cyclodextrins; C062865:2,3-dioxo-6-nitro-7-sulfamoylbenzo(f)quinoxaline; C049853:gabazine; D011280:Pregnanolone