title: Stimulation of nucleoside efflux and inhibition of adenosine kinase by A1 adenosine receptor activation.
abstract: Adenosine is produced intracellularly during conditions of metabolic stress and is an endogenous agonist for four subtypes of G-protein linked receptors. Nucleoside transporters are membrane-bound carrier proteins that transfer adenosine, and other nucleosides, across biological membranes. We investigated whether adenosine receptor activation could modulate transporter-mediated adenosine efflux from metabolically stressed cells. DDT1 MF-2 smooth muscle cells were incubated with 10 microM [3H]adenine to label adenine nucleotide pools. Metabolic stress with the glycolytic inhibitor iodoacetic acid (1AA, 5 mM) increased tritium release by 63% (P < 0.01), relative to cells treated with buffer alone. The IAA-induced increase was blocked by the nucleoside transport inhibitor nitrobenzylthioinosine (1 microM), indicating that the increased tritium release was primarily a purine nucleoside. HPLC verified this to be [3H]adenosine. The adenosine A1 receptor selective agonist N6-cyclohexyladenosine (CHA, 300 nM) increased the release of [3H]purine nucleoside induced by IAA treatment by 39% (P < 0.05). This increase was blocked by the A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (10 microM). Treatment of cells with UTP (100 microM), histamine (100 microM), or phorbol-12-myristate-13-acetate (PMA, 10 microM) also increased [3H]purine nucleoside release. The protein kinase C inhibitor chelerythrine chloride (500 nM) inhibited the increase in [3H]purine nucleoside efflux induced by CHA or PMA treatment. The adenosine kinase activity of cells treated with CHA or PMA was found to be decreased significantly compared with buffer-treated cells. These data indicated that adenosine A1 receptor activation increased nucleoside efflux from metabolically stressed DDT1 MF-2 cells by a PKC-dependent inhibition of adenosine kinase activity.
authors.affiliation: Department of Pharmacology and Therapeutics, University of Manitoba, Winnipeg, Canada.
authors.forename: C J
authors.initials: CJ
authors.lastname: Sinclair
authors.forename: P N
authors.initials: PN
authors.lastname: Shepel
authors.forename: J D
authors.initials: JD
authors.lastname: Geiger
authors.forename: F E
authors.initials: FE
authors.lastname: Parkinson
mesh_terms: D000241:Adenosine / Q000378:metabolism*; D000248:Adenosine Kinase / Q000037:antagonists & inhibitors*; D000818:Animals; D001692:Biological Transport; D002352:Carrier Proteins / Q000378:metabolism; D006224:Cricetinae; D008565:Membrane Proteins / Q000378:metabolism; D033703:Nucleoside Transport Proteins; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D014407:Tumor Cells, Cultured
chemical_list: D002352:Carrier Proteins; D008565:Membrane Proteins; D033703:Nucleoside Transport Proteins; D018047:Receptors, Purinergic P1; D000248:Adenosine Kinase; D000241:Adenosine