Differential effects of P2-purinoceptor antagonists on phospholipase C- and adenylyl cyclase-coupled P2Y-purinoceptors.
1. Stimulation of P2Y-purinoceptors on turkey erythrocytes and many other cell types results in activation of phospholipase C. In contrast, we have observed recently that P2Y-purinoceptors on C6 rat glioma cells are not coupled to phospholipase C, but rather, inhibit adenylyl cyclase. 2. In this study we investigated the pharmacological selectivity of the P2-purinoceptor antagonists, suramin, reactive blue 2, and pyridoxal phosphate 6-azophenyl 2',4'-disulphonic acid (PPADS) for phospholipase C- and adenylyl cyclase-coupled P2Y-purinoceptors. 3. In C6 glioma cells, suramin and reactive blue 2 competitively antagonized the inhibitory effect of 2MeSATP on adenylyl cyclase (pKB = 5.4 +/- 0.2 and 7.6 +/- 0.1, respectively), whereas PPADS at concentrations up to 100 microM had no effect. 4. In contrast, in the turkey erythrocyte preparation, PPADS at concentrations up to 30 microM was a competitive antagonist of P2Y-purinoceptor-stimulated phospholipase C activity (pKB = 5.9 +/- 0.1). Suramin and reactive blue 2 produced both a shift to the right of the concentration-effect of 2MeSATP for the activation of phospholipase C and a significant decrease in the maximal inositol phosphate response. 5. Turkey erythrocytes also express a phospholipase C-coupled beta-adrenoceptor. Concentrations of PPADS that competitively inhibited the P2Y-purinoceptor-mediated response had only minimal effects on the activation of phospholipase C by beta-adrenoceptors. In contrast, suramin and reactive blue 2 produced a non-competitive inhibition, characterized by decreases in the maximal response to isoprenaline with no change in the potency of this beta-adrenoceptor agonist. 6. The differential effect of PPADS on P2Y-purinoceptors of C6 glioma cells and turkey erythrocytes adds further support to the idea that different P2Y-purinoceptor subtypes mediate coupling to adenylylcyclic and phospholipase C.
Department of Pharmacology, School of Medicine, University of North Carolina, Chapel Hill 27599.
J L
JL
Boyer
I E
IE
Zohn
K A
KA
Jacobson
T K
TK
Harden
D000067956:Adenylyl Cyclase Inhibitors; D000262:Adenylyl Cyclases / Q000378:metabolism*; D000818:Animals; D002478:Cells, Cultured; D004910:Erythrocyte Membrane / Q000187:drug effects / Q000201:enzymology; D005910:Glioma / Q000201:enzymology; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D051381:Rats; D018048:Receptors, Purinergic P2 / Q000378:metabolism*; D013498:Suramin / Q000494:pharmacology; D014227:Triazines / Q000494:pharmacology; D014422:Turkeys; D010738:Type C Phospholipases / Q000037:antagonists & inhibitors / Q000378:metabolism*
D000067956:Adenylyl Cyclase Inhibitors; D011500:Protein Synthesis Inhibitors; D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; D014227:Triazines; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; C012842:Cibacron Blue F 3GA; D011732:Pyridoxal Phosphate; D013498:Suramin; D010738:Type C Phospholipases; D000262:Adenylyl Cyclases