A new cyclic AMP-independent, Gs-mediated stimulatory mechanism via the adenosine A2a receptor in the intact cardiac cell.
The objectives of this study were to investigate the mechanism underlying the adenosine A2a receptor (A2aR)-mediated positive inotropic response and to define its contractile function using chick embryo ventricular cells as a model. Activation of the A2aR caused a marked stimulation of calcium entry and cell contractility, which were blocked by verapamil or nifedipine. The effects elicited by maximal concentrations of the A2aR agonist 2-[4-(2-carboxyethyl)phenylethylamino]-5'-N-ethylcarboxamidoadenos ine and the beta-adrenergic agonist isoproterenol were additive, indicating that the two receptors do not share a common stimulatory mechanism. The cAMP antagonist (Rp)-adenosine cyclic 3':5'-monophosphorothioate was ineffective in inhibiting the A2aR-mediated stimulation of contractility or the L-type calcium channel, while it completely abolished the isoproterenol effects. Activation of the A2aR had no effect on Na+/Ca2+ exchange or inositol 1,4,5-trisphosphate accumulation. Blocking of the A2aR resulted in unopposed A1 receptor-mediated inhibitory effects and led to an inhibition of basal contractility and an enhanced anti-adrenergic effect by A1 agonist. The adenosine A2a receptor mediates a new cyclic AMP-independent mechanism and a new contractile function in the cardiac cell.
Liang
B T
BT
Department of Medicine, University of Pennsylvania Medical Center, Philadelphia, Pennsylvania 19104, USA.
Morley
J F
JF
D000241:Adenosine / Q000031:analogs & derivatives / Q000494:pharmacology; D000318:Adrenergic beta-Agonists / Q000494:pharmacology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D002642:Chick Embryo; D000242:Cyclic AMP / Q000378:metabolism; D019204:GTP-Binding Proteins / Q000378:metabolism*; D017136:Ion Transport / Q000187:drug effects; D007545:Isoproterenol / Q000494:pharmacology; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D009206:Myocardium / Q000166:cytology / Q000378:metabolism*; D009543:Nifedipine / Q000494:pharmacology; D010627:Phenethylamines / Q000494:pharmacology; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D014700:Verapamil / Q000494:pharmacology
D000318:Adrenergic beta-Agonists; D002121:Calcium Channel Blockers; D010627:Phenethylamines; D058906:Purinergic P1 Receptor Agonists; D018047:Receptors, Purinergic P1; C061282:2-(4-(2-carboxyethyl)phenethylamino)-5'-N-ethylcarboxamidoadenosine; D014700:Verapamil; D000242:Cyclic AMP; D019204:GTP-Binding Proteins; D009543:Nifedipine; D000241:Adenosine; D007545:Isoproterenol; D002118:Calcium