Separate P2T and P2U purinergic receptors with similar second messenger signaling pathways in UMR-106 osteoblasts
Sistare, F.D.; Rosenzweig, B.A.; Contrera, J.G.; Jordan, B.
Journal of Pharmacology and Experimental Therapeutics 269(3): 1049-1061
1994
ISSN/ISBN: 0022-3565 PMID: 8014849 Document Number: 428432
UMR-106 rat osteogenic sarcoma cells express two calcium signaling P-2 purinergic receptors. One is a P-2U receptor with EC-50's for adenosine triphosphate (ATP) and uridine triphosphate (UTP) of 2.6 and 2.4 mu-M, respectively. The other is a novel P-2T receptor for adenosine diphosphate (ADP) (EC-50 0.4 mu-M), adenosine 5'-O-(2-thiodiphosphate). (EC-50 5 mu-M), 2-methylthio ATP (EC-50 0.2 mu-M), and 2-methylthio ADP (EC-50 0.04 mu-M). Responses to these ligands are desensitized by ADP but not by UTP. Responses to UTP and ATP are desensitized by UTP but not by ADP or adenosine 5'-O-(2-thiodiphosphate). 2-ChloroATP interacts with both receptors at high concentrations but with only the P-2T receptor at low concentrations (EC-50) 0.05 mu-M). The weak platelet P-2T receptor antagonist AMP blocks this P-2T and not the P-2U receptor. Addition of ATP after UTP desensitization Of P-2U receptors inhibits subsequent responsiveness to ADP but evidence for rapid conversion of ATP to ADP complicates interpretation of this apparent antagonism of P-2T receptors by ATP. A subpassage of UMR-106.P135 cells lose P-2U but retain P-2T ligand responsiveness. Activation of either P-2 receptor increases cellular IP-3 concentrations in UMR-106 cells. Neither receptor can activate divalent cation entry as evidenced by their lack of effect on Mn++ quenching of fura-2 fluorescence. Neither receptor can modify parathyroid hormone receptor-mediated elevation of cellular cyclic AMP. This receptor for ADP demonstrates many of the same characteristics of the ADP receptor which we have previously reported as a P-2T receptor expressed in K562 and Dami cells.