engleski

Enhanced binding of [3H]flunitrazepam after chronic exposure of recombinant GABA A receptors expressed in HEK 293 cells to benzodiazepine receptor ligands

Prolonged treatment with benzodiazepines, barbiturates and steroids induces an allosteric uncoupling of GABA and benzodiazepine binding sites, characterized by a decrease in the GABA enhancement of benzodiazepine binding. It has been suggested that this phenomenon may be related to development of tolerance and physical dependence, which appear in animals and humans following prolonged treatment with these drugs. In order to improve our understanding of the above mentioned phenomena, in this study the ability of GABA (1nM - 1mM) to potentiate [3H]flunitrazepam (1nM) binding after chronic (48 h) exposure to the agonist (diazepam) or antagonist (flumazenil) of benzodiazepine binding sites was studied on the recombinant alpha1 beta2 gamma2s GABAA receptors stably expressed in human embryonic kidney (HEK) 293 cells. In membrane preparations obtained from control cells (exposed for 48h to 1 microM GABA), the maximum enhancement (Emax) of [3H]flunitrazepam binding by GABA was 55.6 %, while the concentration of GABA giving a half-maximum enhancement of [3H]flunitrazepam binding (EC50) was 460 nM. Neither the potency nor the efficacy of GABA was changed when cells were exposed for 48 h to flumazenil (1 or 5 microM), diazepam (1 microM) or the combination thereof in the presence of GABA. However, in all these cases the basal [3H]flunitrazepam binding was markedly enhanced, suggesting an increase in the maximum number and/or affinity of benzodiazepine binding sites. Additionally, these results, along with those obtained by following chronic drug-induced changes on the binding site for convulsants, suggest that in the presence of low concentration of GABA, but in the absence of a normal neuronal environment, the mentioned benzodiazepine receptor ligands do not change GABAA receptor function. Whether a longer exposure of recombinant GABAA receptors to these drugs would produce different results, has yet to be determined.

recombinant GABA A receptors; HEK 293 cells; benzodiazepine receptor ligands; chronic treatment

Rad je kao poster prezentiran i na skupu Prvi kongres Hrvatskih znanstvenika iz domovine i inozemstva, održanom od 15.-19.11.2004., Zagreb - Vukovar, Hrvatska ; objavljen u Zbornik sažetaka postera znanstvenih novaka izlaganih u inozemstvu 2002., 2003. i 2004. godine, Vol.2 ; Zlatko Kniewald (ur.) ; Zagreb : Akademija tehničkih znanosti Hrvatske, 2004. ; str. 686.