The effect of PPADS as an antagonist of inositol (1,4,5)trisphosphate induced intracellular calcium mobilization

Abstract

1 Brain capillary endothelial cells responded to uridine 5′-triphosphate (UTP) and adenosine 5′-triphosphate (ATP) by activation of phospholipase C and by large changes in [Ca²⁺]_i. These cells expressed mRNA sequences identical to the sequence of the P_2Y2-purinoceptor of rat pituitaries. 2 Pyridoxalphosphate-6-azophenyl-2′,4′-disulphonic acid (PPADS) at 100 μm did not prevent UTP and ATP induced accumulations of total [³H]-inositol (poly)phosphates. It inhibited UTP and ATP induced intracellular Ca²⁺ mobilization (IC₅₀ = 30 γm) by non competitive mechanism. 3 PPADS (100 μm) inhibited endothelin-1 induced accumulation of total [³H]-inositol (poly)phosphates by less than 20% and prevented most of endothelin-1 induced intracellular Ca²⁺ mobilization (IC₅₀ = 30 μm). 4 PPADS (100 μm) had no action on ionomycin induced intracellular Ca²⁺ mobilization. 5 Microinjection of inositol (1,4,5)trisphosphate (InsP₃) into Xenopus oocytes induced large Ca²⁺ activated Cl⁻ currents that were prevented by heparin and by PPADS. 6 It is concluded that PPADS does not recognize rat P_2Y2-purinoceptors and prevents UTP and ATP induced intracellular Ca²⁺ mobilization by a non-specific mechanism that could involve the inhibition of InsP₃ channels.