engleski

Prolonged exposure of cells expressing recombinant GABA A receptors to flumazenil up-regulates [3H]flunitrazepam binding sites in a bicuculline sensitive manner

In order to improve our understanding of the mechanisms that underlie adaptive changes in GABAA receptors following their prolonged exposure to drugs, we studied the effects of prolonged flumazenil (antagonist of benzodiazepine binding sites) exposure on the recombinant alpha1 beta2 gamma2s GABA A receptors, the most common type of GABAA receptor found in the brain. Stably transfected human embryonic kidney (HEK) 293 cells expressing the alpha1 beta2 gamma2S subtype of GABA A receptor were exposed for 48 h to flumazenil (antagonist of benzodiazepine binding sites), or to flumazenil (5microM) in combination with GABA (50 microM), bicuculline (100 microM), diazepam (1microM) or b-CCM (1 micromM). Aliquots of membrane preparations (~100 microg protein) obtained from control and drug treated cells were used in saturation binding studies with [3H]flunitrazepam (0.2 – 16 nM) under conditions (4°C, 90 min) previously described (Pericic et al., . Eur. J. Pharmacol., 482: 117-125, 2003). As previously observed (Pericic et al., submitted), flumazenil (in the absence of GABA) enhanced the maximum number (Bmax) and the equilibrium dissociation constant (Kd) of [3H]flunitrazepam binding sites. Flumazenil-induced increase in the Bmax value was further enhanced by GABA, diminished by bicuculline (the competitive antagonist of GABA binding sites), and not affected by diazepam, the agonist, or beta-CCM, an inverse agonist of benzodiazepine binding sites. While GABA by itself also up-regulated, diazepam in the absence of GABA failed to affect the number of benzodiazepine binding sites. The results suggest that GABA binding site is involved in chronic flumazenil-induced enhancement of benzodiazepine binding sites in stably transfected HEK 293 cells.

recombinant GABA A receptors; HEK 293 cells; chronic treatment; flumazenil; diazepam; GABA; bicuculline; beta-CCM

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. 752.