The role of adenosine A(1) receptors in the ATP-evoked Ca(2+) response in rat thyroid FRTL-5 cells.
The effect of adenosine A(1) receptor activation on the ATP-induced increase in intracellular free Ca(2+) was studied in control and protein kinase C down-regulated Fisher rat thyroid (FRTL-5) cells. Long-term phorbol ester treatment, which leads to protein kinase C down-regulation, enhanced the ATP-evoked extracellular Ca(2+) influx. The increased Ca(2+) influx was antagonized by the adenosine A(1) receptor antagonist 8-cyclopentyl-1, 3-dipropylxanthine (DPCPX). [3H]DPCPX binding studies revealed that phorbol ester-treatment increased the number of adenosine A(1) receptors. The adenosine A(1) receptor-mediated inhibition of the cyclic AMP formation was not affected by the increased receptor number. We conclude that the enhanced ATP-evoked Ca(2+) influx in protein kinase C down-regulated cells is mediated by adenosine formed by hydrolysis of ATP, and that this adenosine interacts with the increased number of A(1) receptors. The mechanism by which adenosine enhances Ca(2+) entry is not known. Thus, the larger number of adenosine A(1) receptors broadens the spectrum of adenosine A(1) receptor affected signaling systems in FRTL-5 cells.
Vainio
M
M
Department of Biology, Abo Akademi University, BioCity, Tykistökatu 6 A, 20520, Turku, Finland.
Törnquist
K
K
D000243:Adenosine Deaminase / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000067956:Adenylyl Cyclase Inhibitors; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002460:Cell Line; D003470:Culture Media; D015536:Down-Regulation / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000378:metabolism; D011493:Protein Kinase C / Q000235:genetics / Q000378:metabolism; D058915:Purinergic P1 Receptor Antagonists; D011869:Radioligand Assay; D051381:Rats; D018047:Receptors, Purinergic P1 / Q000187:drug effects / Q000502:physiology*; D013961:Thyroid Gland / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism*; D010566:Virulence Factors, Bordetella / Q000494:pharmacology; D014970:Xanthines / Q000494:pharmacology
D000067956:Adenylyl Cyclase Inhibitors; D003470:Culture Media; D004791:Enzyme Inhibitors; D058915:Purinergic P1 Receptor Antagonists; D018047:Receptors, Purinergic P1; D010566:Virulence Factors, Bordetella; D014970:Xanthines; D000255:Adenosine Triphosphate; C051360:1,3-dipropyl-8-cyclopentylxanthine; D011493:Protein Kinase C; D000243:Adenosine Deaminase; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D002118:Calcium