engleski

Long-term exposure of recombinant GABA-A receptors to neurosteroid dehydroepiandrosterone sulfate (DHEAS)

Long-term exposure to a variety of drugs including benzodiazepines, barbiturates and steroids induces different adaptive changes in GABA-A receptors, the major fast inhibitory neurotransmitter receptors in the mammalian brain. In order to better understand the underlying mechanisms, human embryonic kidney (HEK) 293 cells stably expressing recombinant alphalbeta2gamma2S GABA-A receptors (the most common type of GABA-A receptors) were exposed for 24 and 48h to neurosteroid dehydroepiandrosterone sulfate (DHEAS). The aliquots of membrane preparations obtained from control and DHEAS-treated cells were used in the saturation binding studies with [3H]flunitrazepam and [3H]t-butylbicycloorthobenzoate ([3H]TBOB) to determine the possible changes in the binding parameters (Kd and Bmax), as well as in the functional interactions between GABAA receptor binding sites. Exposure of HEK 293 cells stably transfected with recombinant alphalbeta2gamma2S GABA-A receptors to 100 microM DHEAS for 24 and 48h have not changed the maximum number nor the affinity of the binding sites for benzodiazepines and convulsants. Moreover, no significant differences between the groups were observed in the potency (IC50) of DHEAS to modulate [3H]TBOB binding or in the efficacy (Emax) of GABA to potentiate [3H]flunitrazepam binding. These results have demonstrated that unlike benzodiazepines, chronic DHEAS treatment does not affect expression and functional coupling of GABA- A receptor binding sites. If, as previously suggested, allosteric uncoupling is related to the development of functional and behavioral tolerance following prolonged treatment with GABA-A receptor ligands (as in the case of benzodiazepines), then one might presume that chronic treatment with DHEAS will not produce tolerance.

GABA-A receptor; DHEAS; long-term treatment; expression; allosteric uncoupling

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