PPADS selectively antagonizes P2X-purinoceptor-mediated responses in the rabbit urinary bladder.
1. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), an inhibitor of P2X-purinoceptor-mediated responses in rabbit vas deferens, was investigated for its ability to antagonize contractions evoked by alpha,beta-methylene ATP (alpha,beta-MeATP), carbachol and electrical field stimulation in the rabbit urinary bladder detrusor muscle. 2. PPADS. (1-30 microM) caused concentration-dependent inhibition of contractions to the stable P2X-purinoceptor agonist, alpha,beta-MeATP, decreasing the maximum response to alpha,beta-MeATP (30 microM) at concentrations of 3-30 microM. The pD2 value for alpha,beta-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 microM the negative log concentrations of alpha,beta-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 (1-30 microM) 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 microM, did not produce significantly greater antagonism than 10 microM. 4. PPADS (30 microM) 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%. 5. Radioligand binding studies carried out on rabbit bladder membranes with [3H]-alpha,beta-methylene ATP([3H]-alpha,beta-MeATP) showed that PPADS concentration-dependently inhibited the binding of [3H]-alpha,beta-MeATP to P2X-purinoceptors, while the binding of [3H]-quinuclidinyl benzilate to muscarinic cholinoceptors was not affected.6. Thus, PPADS (1-30 microM) 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.
Ziganshin
A U
AU
Department of Anatomy and Developmental Biology, University College London.
Hoyle
C H
CH
Bo
X
X
Lambrecht
G
G
Mutschler
E
E
Bäumert
H G
HG
Burnstock
G
G
D000255:Adenosine Triphosphate / Q000031:analogs & derivatives / Q000378:metabolism; D000818:Animals; D002217:Carbachol / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives* / Q000494:pharmacology; D011817:Rabbits; D018048:Receptors, Purinergic P2 / Q000502:physiology; D001743:Urinary Bladder / Q000187:drug effects* / Q000502:physiology
D058919:Purinergic P2 Receptor Antagonists; D018048:Receptors, Purinergic P2; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D000255:Adenosine Triphosphate; D002217:Carbachol; C002630:alpha,beta-methyleneadenosine 5'-triphosphate