Receptor binding and electrophysiological effects of Dehydroepiandrosterone sulfate, an antagonist of the GABA A receptor

Abstract

Recently we demonstrated that [ 3H]dehydroepiandrosterone sulfate binds specifically to two populations of sites in rat brain membranes [Majewska et al. (1990) Eur. J. Pharmac. 189, 307–315]. As an extension of this work, we studied the biochemical and pharmacological properties of [ 3H]dehydroepiandrosterone sulfate binding to brain membranes and the effects of dehydroepiandrosterone sulfate on GABA-induced currents in cultured neurons. [ 3H]Dehydroepiandrosterone sulfate binding depended upon incubation time, pH, protein concentration, and incubation temperature. Thermal denaturation or pretreatment of the membranes with protease or phospholipase A 2 reduced the binding by 54–85%. The higher affinity [ 3H]dehydroepiandrosterone sulfate binding sites appeared to be associated with protein and with the GABA A receptor complex. Among substances known to interact with the GABA A receptor complex, pregnenolone sulfate, pentobarbital, and phenobarbital inhibited the binding of [ 3H]dehydroepiandrosterone sulfate. High micromolar concentrations of dehydroepiandrosterone sulfate inhibited [ 3H]muscimol and [ 3H]flunitrazepam binding to rat brain membranes, primarily by reducing the binding affinities. Dehydroepiandrosterone sulfate also produced a concentration-dependent block of GABA-induced currents in cultured neurons from ventral mesencephalon ( IC 50 = 13 ± 3μM). The results of this study are consistent with an action of dehydroepiandrosterone sulfate as a negative noncompetitive modulator of the GABA A receptor. Because concentrations of dehydroepiandrosterone sulfate in the brain undergo physiological variations, this neurosteroid may play a vital role in regulation of neuronal excitability in the central nervous system.