title: Adenine nucleotide-induced activation of adenosine A(2B) receptors expressed in Xenopus laevis oocytes: involvement of a rapid and localized adenosine formation by ectonucleotidases.
abstract: We recently demonstrated that extracellular ATP effectively activates adenosine (Ade) A(2B) 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 A(2B) receptor-expressing Xenopus laevis oocytes, which possess endogenous ectonucleotidase activity. In oocytes coexpressing the A(2B) receptor 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 beta,gamma-methylene ATP (beta,gamma-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 alpha,beta-methylene ADP markedly inhibited the beta,gamma-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 A(2B) receptors.
authors.affiliation: Department of Pharmacology, School of Medicine, Fukushima Medical University, Fukushima, Japan. isom@fmu.ac.jp
authors.forename: Isao
authors.initials: I
authors.lastname: Matsuoka
authors.forename: Satoko
authors.initials: S
authors.lastname: Ohkubo
authors.forename: Junko
authors.initials: J
authors.lastname: Kimura
authors.forename: Yasuhito
authors.initials: Y
authors.lastname: Uezono
mesh_terms: D000241:Adenosine / Q000096:biosynthesis* / Q000494:pharmacology; D058892:Adenosine Deaminase Inhibitors; D000249:Adenosine Monophosphate / Q000494:pharmacology; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000818:Animals; D006801:Humans; D009708:Nucleotidases / Q000378:metabolism; D009865:Oocytes / Q000187:drug effects / Q000378:metabolism; D058914:Purinergic Antagonists; D051381:Rats; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1 / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D014982:Xenopus laevis
chemical_list: D058892:Adenosine Deaminase Inhibitors; D058914:Purinergic Antagonists; D043704:Receptor, Adenosine A2B; D018047:Receptors, Purinergic P1; C005147:5'-adenylyl (beta,gamma-methylene)diphosphonate; D000249:Adenosine Monophosphate; D000255:Adenosine Triphosphate; D009708:Nucleotidases; D000241:Adenosine