Comparative studies on the affinities of ATP derivatives for P_2X‐purinoceptors in rat urinary bladder

Abstract

1 Radioligand binding assays have been used to determine the affinities of a series of ATP derivatives with modifications of the polyphosphate chain, adenine and ribose moieties of the ATP molecule for[3H]-z,P-methylene ATP ([3H]-a,P-MeATP) binding sites in rat urinary bladder.2 The replacement of the bridging oxygen in the triphosphate chain of ATP (pIC50 = 5.58) with a methylene or imido group markedly increased the affinity (691 fold in IC50 values for P,V-imidoATP, 15fold for P,y-methylene ATP), and the replacement of an ionized oxygen on the Ty-phosphate with a sulphur (ATPyS) also led to increased affinity (5623 fold in IC, values). 3 Modifications at N6, N', and C-8 positions on the purine base usually reduced the affinity of ATP (a decrease of 2.8 fold in IC50 values for N6-methylATP and 8.9 fold for 8-bromo ATP), while the attachment of an alkylthio group to the C-2 position greatly increased the affinity for P2x-purinoceptors (from 3.5 to 98 fold increase in IC50 values). 4 Replacement of the 3'-hydroxyl group on the ribose with substituted amino or acylamino groups produced more potent P2X-purinoceptor agonists (an increase of 447 fold in ICm values for 3'-deoxy-3'-benzylamino ATP and 28 fold for 3'-deoxy-3'-(4-hydroxyphenylpropionyl)amino ATP.

Agonist trapped in ATP-binding sites of the P2X2 receptor

“…We indeed present evidence that the labeling reaction saturates with increasing NCS-ATP concentrations and is pharmacologically prevented by ATP or by the competitive antagonist TNP-ATP. In addition, we found that the affinity labeling is dependent on the presence of the ATP phosphate tail, because contrary to NCS-ATP no substantial labeling arises at low concentrations of NCS-Ado, a poor P2X ligand (27). Finally, we showed that modification of the side chain at N140 and L186 positions either genetically by site-directed mutagenesis or chemically by MTS derivatives of substituted cysteine profoundly alters ATP function.…”

“…Second, it is known that adenosine (Ado) is a poor P2X ligand (27), and consequently its site occupancy should be lower than that of ATP. Therefore, the apparent rates of the tethering reaction by NCS-Ado should be slower than those determined by NCS-ATP.…”

Discrimination by PPADS between endothelial P2Y‐ and P2U‐ purinoceptors in the rat isolated mesenteric arterial bed

“…PPADS has been shown to block P2y-mediated responses in turkey erythrocytes (Boyer et al, 1994), but is ineffective at P2y receptors in rabbit mesenteric arteries and aorta (Ziganshin et al, 1994). Reactive blue 2 has been proposed as a P2Y-purinoceptor antagonist; however, it has low selectivity, acting also at P2X-purinoceptors (Choo et al, 1980;Bo et al, 1994;Bultmann & Starke, 1994) and is effective only within a narrow concentration-range (Burnstock & Warland, 1987;Hopwood & Burnstock, 1987).…”

Evidence for P2-purinoceptor-mediated uptake of Ca2+ across a fish (Oreochromis mossambicus) intestinal brush border membrane

“…SK&F 96365 was tested at a concentration of 15 µM, which is in the range of the IC &! values reported for different preparations [7,14,15]. Suramin is generally employed at concentrations equal to or higher than the agonist concentration [2,16,17].…”