RT Journal Article SR Electronic T1 Influence of Receptor Number on Functional Responses Elicited by Agonists Acting at the Human Adenosine A1 Receptor: Evidence for Signaling Pathway-Dependent Changes in Agonist Potency and Relative Intrinsic Activity JF Molecular Pharmacology JO Mol Pharmacol FD American Society for Pharmacology and Experimental Therapeutics SP 1075 OP 1084 DO 10.1124/mol.58.5.1075 VO 58 IS 5 A1 Cordeaux, Yolande A1 Briddon, Stephen J. A1 Megson, Anne E. A1 McDonnell, Jacqui A1 Dickenson, John M. A1 Hill, Stephen J. YR 2000 UL http://molpharm.aspetjournals.org/content/58/5/1075.abstract AB Activation of A1 adenosine receptors leads to the inhibition of cAMP accumulation and the stimulation of inositol phosphate accumulation via pertussis toxin-sensitive G-proteins. In this study we have investigated the signaling of the A1adenosine receptor in Chinese hamster ovary (CHO) cells, when expressed at approximately 203 fmol/mg (CHOA1L) and at approximately 3350 fmol/mg (CHOA1H). In CHOA1L cells, the agonistsN 6-cyclopentyladenosine (CPA), (R)-N 6-(2-phenylisopropyl)adenosine, and 5′-(N-ethylcarboxamido)adenosine (NECA) inhibited cAMP production in a concentration-dependent manner. After pertussis toxin treatment, the agonist NECA produced a stimulation of cAMP production, whereas CPA and (R)-N 6-(2-phenylisopropyl)adenosine were ineffective. In CHOAIH cells, however, all three agonists produced both an inhibition of adenylyl cyclase and a pertussis toxin-insensitive stimulation of adenylyl cyclase. All three agonists were more potent at inhibiting adenylyl cyclase in CHOA1H cells than in CHOA1L cells. In contrast, A1 agonists (and particularly NECA) were less potent at stimulating inositol phosphate accumulation in CHOA1H cells than in CHOA1L cells. After pertussis toxin treatment, agonist-stimulated inositol phosphate accumulation was reduced in CHOA1H cells and abolished in CHOA1L cells. The relative intrinsic activity of NECA in stimulating inositol phosphate accumulation, compared to CPA (100%), was much greater in the presence of pertussis toxin (289.6%) than in the absence of pertussis toxin (155.2%). These data suggest that A1 adenosine receptors can couple to both pertussis toxin-sensitive and -insensitive G-proteins in an expression level-dependent manner. These data also suggest that the ability of this receptor to activate different G-proteins is dependent on the agonist present.