Abstract
In this study, we present evidence on the ability of endogenous adenosine to modulate adenylyl cyclase activity in intact PC12 cells. The adenosine receptor antagonists PD 115199, xanthine amine congener, 8-cyclopentyl-1,3-dipropylxanthine, 8-(p-sulfophenyl)theophylline, and 3,7-dimethyl-1-propargylxanthine inhibited 10 μM forskolin-induced cyclic AMP (cAMP) accumulation, with IC50 values of 2.76 ± 1.16 nM, 17.4 ± 1.08 nM, 443 ± 1.03 nM, 2.00 ± 1.01 μM, and 2.25 ± 1.05 μM, respectively. Inhibition by 2.5 nM PD 115199 was only partially reversed by increasing forskolin concentrations up to 100 μM. The addition of PD 115199 with or 60 min after forskolin caused a comparable inhibition of forskolin effect over the next hour. Both exogenous adenosine (0.1 μM) and its precursor, AMP (10 and 100 μM), significantly enhanced forskolin-induced cAMP accumulation, whereas inosine was ineffective. Forskolin activity was also potentiated by the hydrolysis-resistant adenosine receptor agonists 5′-N-ethylcarboxamido adenosine and CGS 21680 (8.9- and 12.2-fold increase, respectively). Adenosine deaminase (1 U/ml) and 8-SPT (25 μM), which nearly abolished the response to 1 μM adenosine, also reduced cAMP accumulation caused by AMP (−78 and −54%, respectively). These results demonstrate that in PC12 cells, activation of adenylyl cyclase by forskolin is highly dependent on the occupancy of A2Aadenosine receptors and that AMP potentially contributes to the amplification of forskolin response.
Footnotes
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Send reprint requests to: Dr. Chiara Florio, Dipartimento di Scienze Biomediche, Via L. Giorgieri, 7/9, 34127 Trieste, Italy. E-mail: florioc{at}univ.trieste.it
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↵1 This work was supported by Ministry of University and of Scientific and Technological Research 60% Grant 1997 of the University of Trieste. These results were presented in a preliminary form at the 6th International Symposium on Adenosine and Adenine Nucleotides (Ferrara, Italy).
- Abbreviations:
- cAMP
- cyclic AMP
- AOPCP
- α,β-methyleneadenosine-5′-diphosphate
- ADA
- adenosine deaminase
- CGS 21680
- 2-[p-(2-carbonylethyl)phenylethylamino]-5′-N-ethylcarboxamidoadenosine, NECA, 5′-N-ethylcarboxamido adenosine
- 8-SPT
- 8-(p-sulfophenyl)theophylline
- DMPX
- 3,7-dimethyl-1-propargylxanthine
- XAC
- xanthine amine congener
- DPCPX
- 8-cyclopentyl-1,3-dipropylxanthine
- PD 115199
- N-[2-(dimethylamino)ethyl]-N-methyl-4-(2,3,6,7-tetrahydro-2,6-dioxo-1,3-dipropyl-1H-purin-8-yl)benzenesulfonamide
- Received September 29, 1998.
- Accepted April 14, 1999.
- The American Society for Pharmacology and Experimental Therapeutics
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