A sub(2A) adenosine-receptor-mediated facilitation of noradrenaline release in rat tail artery involves protein kinase C activation and beta gamma subunits formed after alpha sub(2)-adrenoceptor activation

• Published in: Neurochemistry international 2007-07, Vol.51 (1), p.47-56
• Main Authors: Fresco, Paula, Oliveira, Jorge MA, Kunc, Filip, Soares, Ana Sofia, Rocha-Pereira, Carolina, Goncalves, Jorge, Diniz, Carmen
• Format: Article
• Language: English
• ISSN: 0197-0186
• DOI: 10.1016/j.neuint.2007.03.009

This work aimed to investigate the molecular mechanisms involved in the interaction of alpha sub(2)-adrenoceptors and adenosine A sub(2A)-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 alpha sub(2)-adrenoceptors and A sub(2A)-receptors interact. The selective adenosine A sub(2A)-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 A sub(2A)-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 mu M). CGS 21680-mediated effects were also abolished by drugs that disrupted G sub(i/o)-protein coupling with receptors, PTX (2 mu g/ml) or NEM (40 mu M), by the anti-G sub(s alpha ) peptide (2 mu g/ml) anti-G sub( beta gamma ) peptide (10 mu g/ml) indicating coupling of A sub(2A)- receptors to G sub(s alpha ) and suggesting a crucial role for G sub( beta gamma ) subunits in the A sub(2A)-receptor-mediated enhancement of tritium overflow. Furthermore, phorbol 12-myristate 13-acetate (PMA; 1 mu M) or forskolin (1 mu M), 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 A sub(2A)-receptors couple to G sub(s alpha ) subunits which is essential, but not sufficient, for the release facilitation to occur, requiring the involvement of G sub(i/o)-protein coupling (it disappears after disruption of G sub(i/o)-protein coupling, PTX or NEM) and/or G sub( beta gamma ) subunits (anti-G sub( beta gamma )). 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 sub(s alpha ) subunits (released after adenosine A sub(2A)-receptor activation; prime- activation), G sub( beta gamma ) subunits (released after activation of G sub(i/o)- protein coupled receptors) which can directly synergistically stimulate the prime-activated AC or indirectly via G sub( beta gamma ) activation of the PLC-PKC pathway.