Prolonged exposure to γ-aminobutyric acid up-regulates stably expressed recombinant α1β2γ2s GABA A receptors

Abstract

The aim of this study was to better understand the mechanisms that underlie adaptive changes in GABA A receptors following their prolonged exposure to drugs. Exposure (48 and/or 96 h) of human embryonic kidney (HEK 293) cells stably expressing recombinant α1β2γ2s GABA A receptors for γ-aminobutyric (GABA, 1 mM) and muscimol (100 μM), but not for diazepam (1 μM), enhanced the maximum number ( B max) of [ 3H]flunitrazepam binding sites without affecting their affinity ( K d). The GABA-induced enhancement in B max was reduced by the GABA receptor antagonist, bicuculline (100 μM), and by cycloheximide (10 μl/ml), a protein synthesis inhibitor. GABA (100 μM) enhanced the affinity of [ 3H]flunitrazepam binding to vehicle- and GABA-pretreated, but not to diazepam-pretreated, HEK 293 cells. The results suggest that chronic GABA treatment up-regulates stably expressed GABA A receptors, presumably by stimulating their synthesis. Unlike chronic diazepam, which produced functional uncoupling of GABA and benzodiazepine binding sites, chronic GABA failed to produce this effect.