title: Thyrotropin regulates adenosine A(1) receptor expression in rat thyroid FRTL-5 cells.
abstract: The effect of thyrotropin (TSH), on adenosine A(1) receptor expression in thyroid FRTL-5 cells was examined by [(3)H]-1, 3-dipropyl-,8-cyclopentyl xanthine ([(3)H]-DPCPX) binding on cells in suspension and on membrane preparation, and by in situ mRNA labelling. The estimated K(D) for intact cells was 0.19 nM and about 47,000 binding sites per cell were found in cells constantly grown in the presence of TSH. Three days deprivation of TSH decreased the number of [(3)H]-DPCPX binding sites without any significant effect of K(D). Reintroduction of TSH to the cells returned the higher level of A(1) receptors both in suspension binding studies on whole cells and on membrane preparations. In situ hybridization revealed that TSH evoked an increase in the number of cells densely labelled with a probe against A(1) receptor mRNA. The potency of the A(1) receptor agonist N(6)-cyclohexyladenosine (CHA) as an inhibitor of cyclic AMP formation induced by forskolin was increased in TSH-treated cells, with a shift in the IC(50) from 2.05 nM in TSH-deprived cells to 0.14 nM in TSH-treated cells. Since the activation of A(1) receptors inhibits TSH-mediated cyclic AMP signalling, our results suggest a regulatory feedback mechanism between signalling via adenosine A(1) receptors and TSH receptors.
authors.affiliation: Department of Biology, Division of Genetics and Physiology, University of Turku, Finland.
authors.forename: M
authors.initials: M
authors.lastname: Vainio
authors.forename: B B
authors.initials: BB
authors.lastname: Fredholm
authors.forename: K
authors.initials: K
authors.lastname: Törnquist
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D002478:Cells, Cultured; D058915:Purinergic P1 Receptor Antagonists; D012333:RNA, Messenger / Q000187:drug effects / Q000378:metabolism; D051381:Rats; D018047:Receptors, Purinergic P1 / Q000096:biosynthesis*; D015398:Signal Transduction; D013950:Thymus Gland / Q000187:drug effects* / Q000378:metabolism; D013972:Thyrotropin / Q000494:pharmacology*; D014316:Tritium; D014970:Xanthines / Q000494:pharmacology
chemical_list: D058915:Purinergic P1 Receptor Antagonists; D012333:RNA, Messenger; D018047:Receptors, Purinergic P1; D014970:Xanthines; D014316:Tritium; D013972:Thyrotropin; C051360:1,3-dipropyl-8-cyclopentylxanthine; D000262:Adenylyl Cyclases