THE EFFECT OF PPADS AS AN ANTAGONIST OF INOSITOL (1,4,5)TRISPHOSPHATEINDUCED INTRACELLULAR CALCIUM MOBILIZATION

1 Brain capillary endothelial cells responded to uridine 5'-triphospha te (UTP) and adenosine 5'-triphosphate (ATP) by activation of phosphol ipase C and by large changes in [Ca2+](i). These cells expressed mRNA sequences identical to the sequence of the P-2Y2-purinoceptor of rat p ituitaries. 2 Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (P PADS) at 100 mu M did not prevent UTP and ATP induced accumulations of total [H-3]-inositol (poly)phosphates. It inhibited UTP and ATP induc ed intracellular Ca2+ mobilization (IC50 = 30 mu M) by non competitive mechanism. 3 PPADS (100 mu M) inhibited endothelin-1 induced accumula tion of total [H-3]-inositol (poly)phosphates by less than 20% and pre vented most of endothelin-1 induced intracellular Ca2+ mobilization (I C50 = 30 mu M). 4 PPADS (100 mu M) had no action on ionomycin induced intracellular Ca2+ mobilization. 5 Microinjection of inositol (1,4,5)t risphosphate (InsP(3)) into Xenopus oocytes induced large Ca2+ activat ed Cl- currents that were prevented by heparin and by PPADS. 6 It is c oncluded that PPADS does not recognize rat P-2Y2-purinoceptors and pre vents UTP and ATP induced intracellular Ca2+ mobilization by a non-spe cific mechanism that could involve the inhibition of InsP(3) channels.