title: A2A adenosine-receptor-mediated facilitation of noradrenaline release in rat tail artery involves protein kinase C activation and betagamma subunits formed after alpha2-adrenoceptor activation.
abstract: This work aimed to investigate the molecular mechanisms involved in the interaction of alpha2-adrenoceptors and adenosine A2A-receptor-mediated facilitation of noradrenaline release in rat tail artery, namely the type of G-protein involved in this effect and the step or steps where the signalling cascades triggered by alpha2-adrenoceptors and A2A-receptors interact. The selective adenosine A2A-receptor agonist 2-p-(2-carboxy ethyl) phenethylamino-5'-N-ethylcarboxamidoadenosine (CGS 21680; 100 nM) enhanced tritium overflow evoked by trains of 100 pulses at 5 Hz. This effect was abolished by the selective adenosine A2A-receptor antagonist 5-amino-7-(2-phenyl ethyl)-2-(2-furyl)-pyrazolo-[4,3-e]-1,2,4-triazolo [1,5-c]pyrimidine (SCH 58261; 20 nM) and by yohimbine (1 microM). CGS 21680-mediated effects were also abolished by drugs that disrupted G(i/o)-protein coupling with receptors, PTX (2 microg/ml) or NEM (40 microM), by the anti-G(salpha) peptide (2 microg/ml) anti-G(betagamma) peptide (10 microg/ml) indicating coupling of A2A-receptors to G(salpha) and suggesting a crucial role for G(betagamma) subunits in the A(2A)-receptor-mediated enhancement of tritium overflow. Furthermore, phorbol 12-myristate 13-acetate (PMA; 1 microM) or forskolin (1 microM), direct activators of protein kinase C and of adenylyl cyclase, respectively, also enhanced tritium overflow. In addition, PMA-mediated effects were not observed in the presence of either yohimbine or PTX. Results indicate that facilitatory adenosine A2A-receptors couple to G(salpha) subunits which is essential, but not sufficient, for the release facilitation to occur, requiring the involvement of G(i/o)-protein coupling (it disappears after disruption of G(i/o)-protein coupling, PTX or NEM) and/or G(betagamma) subunits (anti-G(betagamma)). We propose a mechanism for the interaction in study suggesting group 2 AC isoforms as a plausible candidate for the interaction site, as these isoforms can integrate inputs from G(salpha) subunits (released after adenosine A2A-receptor activation; prime-activation), G(betagamma) subunits (released after activation of G(i/o)-protein coupled receptors) which can directly synergistically stimulate the prime-activated AC or indirectly via G(betagamma) activation of the PLC-PKC pathway.
authors.affiliation: Serviço de Farmacologia, REQUIMTE/FARMA, Faculdade de Farmácia, Universidade do Porto, Rua Aníbal Cunha, 164, P 4050-047 Porto, Portugal. pfresco@ff.up.pt
authors.forename: Paula
authors.initials: P
authors.lastname: Fresco
authors.forename: Jorge M A
authors.initials: JM
authors.lastname: Oliveira
authors.forename: Filip
authors.initials: F
authors.lastname: Kunc
authors.forename: Ana Sofia
authors.initials: AS
authors.lastname: Soares
authors.forename: Carolina
authors.initials: C
authors.lastname: Rocha-Pereira
authors.forename: Jorge
authors.initials: J
authors.lastname: Gonçalves
authors.forename: Carmen
authors.initials: C
authors.lastname: Diniz
mesh_terms: D000262:Adenylyl Cyclases / Q000187:drug effects / Q000378:metabolism; D000322:Adrenergic Agonists / Q000494:pharmacology; D018674:Adrenergic Antagonists / Q000494:pharmacology; D000818:Animals; D001158:Arteries / Q000187:drug effects / Q000294:innervation / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects / Q000502:physiology; D044387:GTP-Binding Protein beta Subunits / Q000096:biosynthesis* / Q000187:drug effects; D044388:GTP-Binding Protein gamma Subunits / Q000096:biosynthesis* / Q000187:drug effects; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects / Q000294:innervation / Q000378:metabolism; D009638:Norepinephrine / Q000378:metabolism*; D011493:Protein Kinase C / Q000187:drug effects / Q000378:metabolism*; D021122:Protein Subunits / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D020239:Receptor Cross-Talk / Q000187:drug effects / Q000502:physiology; D043705:Receptor, Adenosine A2A / Q000187:drug effects / Q000378:metabolism*; D018341:Receptors, Adrenergic, alpha-2 / Q000187:drug effects / Q000378:metabolism*; D043562:Receptors, G-Protein-Coupled / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology; D017779:Sympathetic Fibers, Postganglionic / Q000187:drug effects / Q000378:metabolism; D013623:Tail / Q000098:blood supply
chemical_list: D000322:Adrenergic Agonists; D018674:Adrenergic Antagonists; C118981:G-protein Beta gamma; D044387:GTP-Binding Protein beta Subunits; D044388:GTP-Binding Protein gamma Subunits; D021122:Protein Subunits; D043705:Receptor, Adenosine A2A; D018341:Receptors, Adrenergic, alpha-2; D043562:Receptors, G-Protein-Coupled; D011493:Protein Kinase C; D000262:Adenylyl Cyclases; D009638:Norepinephrine