PPADS and suramin as antagonists at cloned P 2Y ‐ and P 2U ‐purinoceptors

• Published in: British journal of pharmacology Vol. 118; no. 3; pp. 704 - 710
• Main Authors: Charlton, Steven J., Brown, Colin A., Weisman, Gary A., Turner, John T., Erb, Laurie, Boarder, Michael R.
• Format: Journal Article
• Language: English
• Published: 01.06.1996
• ISSN: 0007-1188; 1476-5381
• DOI: 10.1111/j.1476-5381.1996.tb15457.x

The effect of suramin and pyridoxalphosphate‐6‐azophenyl‐2′,4′‐disulphonic acid (PPADS) on the stimulation of phospholipase C in 1321N1 cells transfected with the human P 2U ‐purinoceptor (h‐P 2U ‐1321N1 cells) or with the turkey P 2Y ‐purinoceptor (t‐P 2Y ‐1321N1 cells) was investigated. 2‐Methylthioadenosine triphosphate (2MeSATP) was used as the agonist at t‐P 2Y ‐1321N1 cells and uridine triphosphate (UTP) at h‐P 2U ‐1321N1 cells. Suramin caused a parallel shift to the right of the concentration‐response curves for 2MeSATP in the t‐P 2Y ‐1321N1 cells, yielding a Schild plot with a slope of 1.16 ± 0.08 and a pA 2 value of 5.77 ± 0.11. Suramin also caused a shift to the right of concentration‐response curves for UTP in the h‐P 2U ‐1321N1 cells, and on Schild plots gave a slope different from unity (1.57 ± 0.19) and an apparent pA 2 value of 4.32 ± 0.13. Suramin was therefore a less potent antagonist at the P 2U ‐purinoceptor than the P 2Y ‐purinoceptor. In the presence of the ectonucleotidase inhibitor, ARL 67156 (6‐N,N‐diethyl‐β,γ‐dibromomethylene‐D‐ATP) there was no significant difference in the EC 50 or shapes of curves with either cell type, and no difference in pA 2 values for suramin. PPADS caused an increase in the EC 50 for 2MeSATP in the t‐P 2Y ‐1321N1 cells. The Schild plot had a slope different from unity (0.55 ± 0.15) and an X‐intercept corresponding to an apparent pA 2 of 5.98 ± 0.65. PPADS up to 30 μ m had no effect on the concentration‐response curve for UTP with the h‐P 2U ‐1321N1 cells. In conclusion, suramin and PPADS show clear differences in their action at the 2 receptor types, in each case being substantially more effective as an antagonist at the P 2Y ‐purinoceptor than at the P 2U ‐purinoceptor. Ectonucleotidase breakdown had little influence on the nature of the responses at the two receptor types, or in their differential sensitivity to suramin.