Effects of neurosteroid and benz[e]indene enantiomers on GABAA receptors in cultured hippocampal neurons and transfected HEK-293 cells.
The effects of the enantiomers of the neurosteroid, 3 alpha-hydroxy-5 alpha-pregnan-20-one (DHP), and the benz[e]indene, BI-1, on gamma-aminobutyric acid (GABA) responses were studied using whole-cell recording techniques in cultured rat hippocampal neurons and human embryonic kidney cells (HEK-293) transfected with either alpha 1 beta 2 gamma 2 or alpha 6 beta 2 gamma 2 GABAA receptor subunits. At 10 microM, the (+)-enantiomers enhanced currents gated by 2 microM GABA in all cells, whereas the (-)-enantiomers were significantly less effective. The enhancement of 2 microM GABA responses in HEK-293 cells transfected with alpha 6 beta 2 gamma 2 subunits was about half that of hippocampal neurons or HEK-293 cells transfected with alpha 1 beta 2 gamma 2. The lower sensitivity of alpha 6 beta 2 gamma 2 receptors for (+)-DHP and (+)-BI-1 is accounted for by their greater apparent affinity for GABA. When the GABA concentration was decreased to 0.5 microM to take into account the four-fold higher apparent affinity of alpha 6 beta 2 gamma 2 receptors, these receptors exhibited enhancement similar to alpha 1 beta 2 gamma 2 receptors. These results indicate that both native and recombinant GABAA receptors have enantioselective sites at which neurosteroids and benz[e]indenes modulate GABA responses, and that differences in agonist affinity contribute to apparent differences in steroid sensitivity among GABAA receptors.
Zorumski
C F
CF
Department of Psychiatry, Washington University Medical School, St Louis, MO 63110, USA.
Wittmer
L L
LL
Isenberg
K E
KE
Hu
Y
Y
Covey
D F
DF
D000818:Animals; D002460:Cell Line; D002478:Cells, Cultured; D004594:Electrophysiology; D006624:Hippocampus / Q000187:drug effects* / Q000502:physiology; D006801:Humans; D007192:Indenes / Q000494:pharmacology*; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D009474:Neurons / Q000187:drug effects* / Q000502:physiology; D018408:Patch-Clamp Techniques; D011280:Pregnanolone / Q000494:pharmacology*; D051381:Rats; D011963:Receptors, GABA-A / Q000187:drug effects* / Q000502:physiology; D013237:Stereoisomerism; D014162:Transfection
D007192:Indenes; D011963:Receptors, GABA-A; D011280:Pregnanolone