EVIDENCE AGAINST THE PRESENCE OF A2 ADENOSINE RECEPTORS ON GUINEA-PIG VENTRICULAR MYOCYTES

The effects of different adenosine agonists on cAMP levels in isolated adult guinea pig ventricular myocytes were investigated. 2-Chloro-N6-cyclopentyladenosine (CCPA), R-N6-phenylisopropyl-adenosine (R-PIA), S-N6-phenylisopropyladenosine (S-PIA) and 5'-N-ethylcarboxamidoadenosine (NECA) reduced isoprenaline-stimulated cAMP levels. Both the nonselective adenosine antagonist 8-{4-[([{(2-aminoethyl)amino}carbonyl]methyl)oxy]-phenyl}-1,3-dipropylxanthine ('xanthine amine congener'; XAC) and the A1-selective adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) blocked the inhibitory effect of NECA. Basal cAMP levels were not altered by NECA or the highly A2-selective 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamidoadenosine (CGS 21680), either alone or in the presence of DPCPX or XAC. These results provide evidence against the existence of A2 receptors on the ventricular myocyte but support the presence of A1 receptors.