title: Adenosine activating A(2A)-receptors coupled to adenylate cyclase/cyclic AMP pathway downregulates nicotinic autoreceptor function at the rat myenteric nerve terminals.
abstract: In addition to the somatodendritic region, myenteric motoneuron terminals are endowed with nicotinic autoreceptors. We aimed at investigating the effect of nicotinic receptor (nAChR) activation on [3H]-acetylcholine ([3H]-ACh) release from longitudinal muscle-myenteric plexus of the rat ileum and to evaluate whether this could be modulated by adenosine, an endogenous neuromodulator typically operating changes in intracellular cyclic AMP. The nAChR agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP, 1-30 microM, 3 min) increased [3H]-ACh release in a concentration-dependent manner. DMPP (30 microM)-induced [3H]-ACh outflow was attenuated by hexamethonium (0.1-1 mM), tubocurarine (1-5 microM), or by removing external Ca2+ (plus EGTA, 1 mM). In contrast to veratridine (0.2-10 microM)-induced [3H]-ACh release, the DMPP (30 microM)-induced outflow was resistant to tetrodotoxin (1 microM) and cadmium (0.5 mM). Pretreatment with adenosine deaminase (0.5 U/mL) or with the adenosine A(2A)-receptor antagonist, ZM 241385 (50 nM), enhanced nAChR-induced transmitter release. Activation of A(2A) receptors with CGS 21680C (3 nM) reduced the DMPP-induced release of [3H]-ACh. CGS 21680C (3 nM) inhibition was prevented by MDL 12,330A (10 microM, an adenylate cyclase inhibitor) and by H-89 (10 microM, an inhibitor of protein kinase A), but was potentiated by rolipram (300 microM, a phosphodiesterase inhibitor). DMPP-induced transmitter release was decreased by 8-bromo-cyclic AMP (1 mM, a protein kinase A activator), rolipram (300 microM), and forskolin (3 microM, an activator of adenylate cyclase). Both MDL 12,330A (10 microM) and H-89 (10 microM) facilitated DMPP-induced release of [3H]-ACh. The results indicate that nAChR-induced [3H]-ACh release is triggered by the influx of Ca2+, independent of voltage-sensitive calcium channels, presumably directly through nAChRs located on myenteric axon terminals. It was also shown that endogenous adenosine, activating A(2A) receptors coupled to the adenylate cyclase/cyclic AMP transducing system, is tonically downregulating this nAChR-mediated control of [3H]-ACh release.
authors.affiliation: Laboratório de Farmacologia/UMIB, Instituto de Ciências Biomédicas de Abel Salazar (ICBAS), Universidade do Porto, L. Prof. Abel Salazar 2, 4099-003 Porto, Portugal.
authors.forename: Margarida
authors.initials: M
authors.lastname: Duarte-Araújo
authors.forename: M Alexandrina
authors.initials: MA
authors.lastname: Timóteo
authors.forename: Paulo
authors.initials: P
authors.lastname: Correia-de-Sá
mesh_terms: D000109:Acetylcholine / Q000378:metabolism; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000502:physiology*; D000818:Animals; D017660:Autoreceptors / Q000187:drug effects / Q000502:physiology; D002118:Calcium / Q000502:physiology; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D015536:Down-Regulation / Q000187:drug effects / Q000502:physiology*; D004558:Electric Stimulation; D020536:Enzyme Activators; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D007082:Ileum / Q000294:innervation; D008297:Male; D009197:Myenteric Plexus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D009411:Nerve Endings / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D018722:Nicotinic Agonists / Q000494:pharmacology; D010726:Phosphodiesterase Inhibitors / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D043705:Receptor, Adenosine A2A / Q000502:physiology*; D011978:Receptors, Nicotinic / Q000187:drug effects / Q000502:physiology*
chemical_list: D058908:Adenosine A2 Receptor Agonists; D058917:Adenosine A2 Receptor Antagonists; D000067956:Adenylyl Cyclase Inhibitors; D017660:Autoreceptors; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D018722:Nicotinic Agonists; D010726:Phosphodiesterase Inhibitors; D043705:Receptor, Adenosine A2A; D011978:Receptors, Nicotinic; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D000262:Adenylyl Cyclases; D000109:Acetylcholine; D002118:Calcium