Adenine Nucleotide-Induced Activation of Adenosine A2B Receptors Expressed in Xenopus laevisOocytes: Involvement of a Rapid and Localized Adenosine Formation by Ectonucleotidases
- 1Department of Pharmacology, School of Medicine, Fukushima Medical University, Fukushima, Japan (I.M., S.O., J.K.); and 2Department of Pharmacology II, Nagasaki University, School of Medicine, Nagasaki, Japan (Y.U.)
- Dr. Isao Matsuoka, Department of Pharmacology, School of Medicine, Fukushima Medical University, 1 Hikarigaoka, Fukushima 960-1295, Japan. E-mail: isom{at}fmu.ac.jp
Abstract
We recently demonstrated that extracellular ATP effectively activates adenosine (Ade) A2B receptors indirectly through a localized rapid conversion to Ade by ectonucleotidases on the membrane surface of C6Bu-1 rat glioma cells. These responses were observed even in the presence of adenosine deaminase (ADA). Here, we demonstrate that such responses indeed occur in A2B receptor-expressingXenopus laevis oocytes, which possess endogenous ectonucleotidase activity. In oocytes coexpressing the A2Breceptor and cystic fibrosis transmembrane conductance regulator (CFTR), Ade induced a concentration-dependent increase in a cyclic AMP-activated CFTR current, a response that was inhibited by the P1 antagonist xanthine-amine congener (XAC). A brief application of ATP and β,γ-methylene ATP (β,γ-MeATP) also induced the CFTR current in a manner similar to that seen with Ade. Among several nucleotide agonists, ADP, AMP, and adenosine-5′-O-(3-thio)triphosphate induced the CFTR current. Although adenine nucleotide-induced CFTR currents were inhibited by XAC, they were highly resistant to ADA treatment; 5 U/ml ADA was required for inhibition of adenine nucleotide-induced CFTR current, whereas 1 U/ml ADA was sufficient to abolish the Ade-induced response. In addition, the ecto-5′-nucleotidase inhibitor α,β-methylene ADP markedly inhibited the β,γ-MeATP-induced response but not the Ade-induced one. These results support our hypothesis that adenine nucleotides are rapidly and locally converted into Ade on the membrane surface, resulting in the activation of A2B receptors.
Footnotes
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This work was supported by Grant-in-Aid 10670092 for Scientific Research from the Ministry of Education, Science, and Culture of Japan and the Smoking Research Foundation in Japan.
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Current address: Department of Cellular Signaling, Graduate School of Pharmaceutical Sciences, Tohoku University, Sendai 980-8578, Japan.
- Abbreviations:
- Ade
- adenosine
- ADA
- adenosine deaminase
- α,β-MeATP
- α,β-methylene ATP
- MBS
- modified Barth's solution
- XAC
- xanthine-amine congener (8-[4-[[[[(2-aminoethyl)amino]carbonyl] methyl]oxy]phenyl]-1,3-dipropylxanthine)
- PPADS
- pyridoxalphosphate-6-azophenyl-2′, 4′-disulfonic acid
- β,γ-MeATP
- β,γ-methylene ATP
- HPLC
- high-performance liquid chromatography
- α,β-MeADP
- α,β-methylene ADP
- ATPγS
- adenosine-5′-O-(3-thio)triphosphate
- 2MeS-ATP
- 2-methylthio ATP
- CFTR
- cystic fibrosis transmembrane conductance regulator
- Epi
- epinephrine
- PCR
- polymerase chain reaction
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- Received August 8, 2001.
- Accepted December 7, 2001.
- The American Society for Pharmacology and Experimental Therapeutics
