title: Allosteric modulation of GABA(B) receptor function in human frontal cortex.
abstract: In the present study, the effects of different allosteric modulators on the functional activity of gamma-aminobutyric acid (GABA)B receptors in membranes of post-mortem human frontal cortex were examined. Western blot analysis indicated that the tissue preparations expressed both GABA(B1) and GABA(B2) subunits of the GABA(B) receptor heterodimer. In [35S]-GTPgammaS binding assays, Ca2+ ion (1 mM) enhanced the potency of the agonists GABA and 3-aminopropylphosphinic acid (3-APA) and that of the antagonist CGP55845, but not that of the GABA(B) receptor agonist (-)-baclofen. CGP7930 (2,6-di-t-Bu-4-(3-hydroxy-2,2-dimethyl-propyl)-phenol), a positive allosteric modulator of GABA(B) receptors, potentiated both GABA(B) receptor-mediated stimulation of [35S]-GTPgammaS binding and inhibition of forskolin (FSK)-stimulated adenylyl cyclase activity. Chelation of Ca2+ ion by EGTA reduced the CGP7930 enhancement of GABA potency in stimulating [35S]-GTPgammaS binding by two-fold. Fendiline, also reported to act as a positive allosteric modulator of GABA(B) receptors, failed to enhance GABA stimulation of [35S]-GTPgammaS binding but inhibited the potentiating effect of CGP7930. The inhibitory effect was mimicked by the phenothiazine antipsychotic trifluoperazine (TFP), but not by other compounds, such as verapamil or diphenydramine (DPN). These data demonstrate that the function of GABA(B) receptors of human frontal cortex is positively modulated by Ca2+ ion and CGP7930, which interact synergistically. Conversely, fendiline and trifluoperazine negatively affect the allosteric regulation by CGP7930.
authors.affiliation: Department of Neuroscience, Section of Biochemical Pharmacology, University of Cagliari, 09042 Monserrato, CA, Italy.
authors.forename: Maria C
authors.initials: MC
authors.lastname: Olianas
authors.forename: Rossano
authors.initials: R
authors.lastname: Ambu
authors.forename: Luciana
authors.initials: L
authors.lastname: Garau
authors.forename: Pierluigi
authors.initials: P
authors.lastname: Onali
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002118:Calcium / Q000494:pharmacology; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002462:Cell Membrane / Q000502:physiology; D005576:Colforsin / Q000494:pharmacology; D004155:Diphenhydramine / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000494:pharmacology; D019204:GTP-Binding Proteins / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006634:Histamine H1 Antagonists / Q000494:pharmacology; D006801:Humans; D008297:Male; D008875:Middle Aged; D010636:Phenols / Q000494:pharmacology; D017397:Prefrontal Cortex / Q000502:physiology*; D018080:Receptors, GABA-B / Q000187:drug effects / Q000502:physiology*; D014268:Trifluoperazine / Q000494:pharmacology; D014700:Verapamil / Q000494:pharmacology
chemical_list: C438607:2,6-di-tert-butyl-4-(3-hydroxy-2,2-dimethylpropyl)phenol; D002121:Calcium Channel Blockers; D018492:Dopamine Antagonists; D006634:Histamine H1 Antagonists; D010636:Phenols; D018080:Receptors, GABA-B; D005576:Colforsin; D014268:Trifluoperazine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D004155:Diphenhydramine; D014700:Verapamil; D019204:GTP-Binding Proteins; D000262:Adenylyl Cyclases; D002118:Calcium