Adenosine A1 receptors and erythropoietin production.
N6-cyclopentyladenosine (CPA), a selective adenosine A1 receptor agonist, in a concentration range of 10(-9) to 10(-7) M, produced a significant decrease in erythropoietin (EPO) levels in a human hepatocellular carcinoma (Hep G2) cell culture (medium levels of EPO, 91.81 +/- 1.61 and 94.36 +/- 0.97% of control, respectively) after 24 h incubation in a hypoxic atmosphere. CPA, at a concentration of 10(-9) M, also produced a significant decrease in Hep G2 cell levels of adenosine 3',5'-cyclic monophosphate (cAMP; 78.13 +/- 3.89% of control) after 2 h incubation. CPA (10(-9) M) also significantly inhibited forskolin-stimulated increases in EPO production and cAMP accumulation in Hep G2 cells. On the other hand, 2-[p-(2-carboxyethyl)phenethyl-amino]-5'-N-ethylcarboxamidoadenosine (CGS-21680), a selective adenosine A2-receptor agonist, produced no significant change in EPO production in a dose range of 10(-10) to 10(-6) M but increased cAMP accumulation at 10(-6) M. A1-receptor binding assays using N6-[3H]cyclohexyladenosine revealed a single type of adenosine receptor binding site on Hep G2 cell membranes with a dissociation constant of 71.4 nM and a binding capacity of 1,530 fmol/mg protein. These results indicate that Hep G2 cells contain high-affinity adenosine A1 receptors that are linked to decreased cAMP accumulation and EPO production.
Ohigashi
T
T
Department of Pharmacology, Tulane University School of Medicine, New Orleans, Louisiana 70112.
Brookins
J
J
Fisher
J W
JW
D000241:Adenosine / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D006528:Carcinoma, Hepatocellular / Q000378:metabolism* / Q000473:pathology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D004921:Erythropoietin / Q000096:biosynthesis*; D006801:Humans; D008113:Liver Neoplasms / Q000378:metabolism* / Q000473:pathology; D018047:Receptors, Purinergic P1 / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D018047:Receptors, Purinergic P1; D004921:Erythropoietin; D005576:Colforsin; C027513:N(6)-cyclohexyladenosine; C048599:N(6)-cyclopentyladenosine; D000242:Cyclic AMP; D000241:Adenosine