PPADS selectively antagonizes P_2X‐purinoceptor‐mediated responses in the rabbit urinary bladder

Abstract

1 Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), an inhibitor of P2x-purinoceptormediated responses in rabbit vas deferens, was investigated for its ability to antagonize contractions evoked by a,B-methylene ATP (a,P-MeATP), carbachol and electrical field stimulation in the rabbit urinary bladder detrusor muscle.2 PPADS (1-30 gM) caused concentration-dependent inhibition of contractions to the stable P2X-purinoceptor agonist, cx,,-MeATP, decreasing the maximum response to a,4-MeATP (30 JAM) at concentrations of 3-30 JiM. The pD2 value for a,4-MeATP in the absence of PPADS was 6.52 ± 0.10 (8). In the presence of PPADS at concentrations of 1, 3, 10 and 30 gM the negative log concentrations of a,4-MeATP that cause the same contractile response as the pD2 value were significantly different from control, being respectively 6.17 ± 0.09 (8), 5.64 ± 0.12 (7), 5.15 ± 0.23 (7) and 4.78 ± 0.22 (5). 3 PPADS (1-30IM) caused concentration-dependent inhibition of contractions to stimulation of intramural purinergic nerves (1 -32 Hz). There was a greater inhibition at lower frequencies (1-8 Hz)than at higher frequencies (16-32 Hz). PPADS, 30 JAM, did not produce significantly greater antagonism than 1OIJM. 4 PPADS (30 jAM) had no significant influence on the contractile potency of carbachol: the pD2 values of carbachol in the absence and presence of PPADS were not significantly different being 6.42 ± 0.16 (5) and 6.33 ± 0.18 (5), respectively. However, PPADS caused a small, but significant, suppression of the maximal response of carbachol, reducing it by approximately 9%. 6 Thus, PPADS (1-30 JM) antagonized responses mediated via P2X-purinoceptors in the rabbit urinary bladder. It was selective for P2-purinoceptor-mediated contractions rather than those mediated via muscarinic receptors. Binding studies demonstrated that the antagonistic effect of PPADS is via a direct interaction with P2x-purinoceptors.

Effects of PPADS and suramin on contractions and cytoplasmic Ca2+ changes evoked by AP4A, ATP and α,β‐methylene ATP in guinea‐pig urinary bladder

“…In the present study, AP4A, ATP and a,fl-methylene ATP produced transient contractions of the outer longitudinal muscle from guinea-pig urinary bladder. The AP4A-, ATP-and a,#-methylene ATP-induced contractions were concentration-dependently suppressed by PPADS, a selective P2X-purinoceptor antagonist, as demonstrated in the rabbit vasa deferentia (Lambrecht et al, 1992), urinary bladder (Ziganshin et al, 1993) and blood vessels (Ziganshin et al, 1994) and guinea-pig vas deferens (McLaren et al, 1994). In addition, these agonist-evoked contractions were also inhibited by suramin, an antagonist of P2-purinoceptors as reported previously for the vas deferens of mouse (Dunn & Blakely, 1988) and urinary bladder (Hoyle et al, 1990), ileum and vas deferens (Katsuragi et al, 1991;Bailey & Hourani, 1995) (Hourani & Chown, 1989) and rabbit ear artery (Crack et al, 1994) although further investigation is needed for understanding this in detail.…”

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

“…Time (min) Figure 5 The lack of an effect of PPADS on ionomycin induced intracellular Ca2 + mobilization. Cells were exposed to 100 pM PPADS (0) or vehicle (0) antagonist of P2X-purinoceptors (Lambrecht et al, 1992;Ziganshin et al, 1993) and of P2YI-purinoceptors (Brown et al, 1995). Its interaction with P2u-purinoceptors is less clear.…”

“…A 10 gM concentration of PPADS is sufficient to block most of the P2X and P2YI-purinoceptor-mediated responses (Lambrecht et al, 1992;Ziganshin et al, 1993;Brown et al, 1995 …”

“…Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) has been shown to act as a potent antagonist of P2x-purinoceptors (Lambrecht et al, 1992;Ziganshin et al, 1993). It was also shown to be an antagonist of P2y-purinoceptors, albeit with a lower potency.…”

PPADS: an antagonist at endothelial P2Y‐purinoceptors but not P2U‐purinoceptors

“…purinoceptors to effect antagonism in the low micromolar range (Lamprecht et al, 1992;Ziganshin et al, 1993) and has been used as a P2x-antagonist in several further studies (e.g. Trezise et al, 1994;Connolly et al, 1995).…”