EFFECTS OF NEUROSTEROID AND BENZ[E]INDENE ENANTIOMERS ON GABA(A) 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-amin obutyric acid (GABA) responses were studied using whole-cell recording techniques in cultured rat hippocampal neurons and human embryonic ki dney cells (HEK-293) transfected with either alpha 1 beta 2 gamma 2 or alpha 6 beta 2 gamma 2 GABA(A) receptor subunits. At 10 mu M, the (+) -enantiomers enhanced currents gated by 2 mu M GABA in all cells, wher eas the (-)-enantiomers were significantly less effective. The enhance ment of 2 mu M GABA responses in HEK-293 cells transfected with alpha 6 beta 2 gamma 2 subunits was about half that of hippocampal neurons o r HEK-293 cells transfected with alpha 1 beta 2 gamma 2. The lower sen sitivity 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 mu M to take into account the four-fold higher apparent affinity of alpha 6 beta 2 gamma 2 receptor s, these receptors exhibited enhancement similar to alpha 1 beta 2 gam ma 2 receptors. These results indicate that both native and recombinan t GABA(A) receptors have enantioselective sites at which neurosteroids and benz[e]indenes modulate GABA responses, and that differences in a gonist affinity contribute to apparent differences in steroid sensitiv ity among GABA(A) receptors. Copyright (C) 1996 Elsevier Science Ltd