title: Rat brain guanosine binding site. Biological studies and pseudo-receptor construction.
abstract: Rat brain guanosine binding sites were studied by (i). a pharmacological approach to confirm the hypothesis of the existence of specific G-coupled receptors for guanosine (1) and, for the first time, delineate a structure-activity relationship for a series of guanosine derivatives; (ii). a molecular modelling approach to design a pseudo-receptor construction. GTP and its non-hydrolysable analogue Gpp[NH]p decreased [3H]-guanosine binding to rat brain membranes. Gpp[NH]p 30 and 100 microM induced a dose-dependent decrease in [3H]-guanosine affinity and PTX pretreatment of rat brain membranes caused a 50% reduction in binding. In slices from rat brain cortex, guanosine induced a dose-dependent increase in intracellular cAMP. This increase is specific for guanosine, since neither the pretreatment with adenosine deaminase nor the A(1) and A(2) adenosine receptor antagonists were able to modify the guanosine-induced cAMP accumulation. The structure-activity relationship showed that the potency order of the best substances able to displace 50 nM [3H]-guanosine was guanosine (1)=6-thioguanosine (3)>8-bromoguanosine (4)>inosine (10)>7-methylguanosine (6)=3'-deoxyguanosine (9)>2'-deoxyguanosine (8)=guanine (11)=6-thioguanine (12)>>N(2)-methylguanosine (5). The competition studies confirmed that [3H]-guanosine site was distinct from the well characterized ATP and adenosine binding sites. The present results are rationalized in terms of a putative pseudo-receptor construct which includes all the relevant physicochemical interaction between guanosine analogues and their putative binding sites. This construct will be useful for the in silico screening of compound libraries in search for new potent and structurally diverse pharmacological tools.
authors.affiliation: Dipartimento di Scienze Biomediche - BRAIN Center, via L Giorgieri 7, Università di Trieste, 34127 Trieste, Italy.
authors.forename: Ugo
authors.initials: U
authors.lastname: Traversa
authors.forename: Giulia
authors.initials: G
authors.lastname: Bombi
authors.forename: Emidio
authors.initials: E
authors.lastname: Camaioni
authors.forename: Antonio
authors.initials: A
authors.lastname: Macchiarulo
authors.forename: Gabriele
authors.initials: G
authors.lastname: Costantino
authors.forename: Clara
authors.initials: C
authors.lastname: Palmieri
authors.forename: Francesco
authors.initials: F
authors.lastname: Caciagli
authors.forename: Roberto
authors.initials: R
authors.lastname: Pellicciari
mesh_terms: D000178:Acrylamides / Q000494:pharmacology; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D001921:Brain / Q000378:metabolism*; D002462:Cell Membrane / Q000378:metabolism; D003064:Cnidarian Venoms; D000242:Cyclic AMP / Q000378:metabolism; D006150:Guanine Nucleotides / Q000494:pharmacology; D006151:Guanosine / Q000378:metabolism* / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D066298:In Vitro Techniques; D008297:Male; D008958:Models, Molecular; D015394:Molecular Structure; D011869:Radioligand Assay; D051381:Rats; D017208:Rats, Wistar; D000095702:Polyether Toxins
chemical_list: D000178:Acrylamides; D003064:Cnidarian Venoms; D000242:Cyclic AMP; D006150:Guanine Nucleotides; D006151:Guanosine; D006160:Guanosine Triphosphate; C010272:palytoxin; D000095702:Polyether Toxins