title: The purinoceptors of the guinea-pig isolated taenia caeci.
abstract: The guinea-pig taenia caeci contains both P1 and P2 purinoceptors mediating relaxation. The P2 purinoceptors have been further characterized using an experimental approach designed to minimise complicating factors. In the presence of the adenosine uptake inhibitor S-(4-nitrobenzyl)-6-thioinosine (NBTI, 300 nM) and a pA100 concentration of the P1 purinoceptor antagonist 8-sulphophenyltheophylline (140 microM), the potency order of agonists was: 2-methylthio-ATP >> adenosine 5'-triphosphate (ATP) = alpha, beta-methylene ATP > beta, gamma-methylene ATP >> uridine 5'-triphosphate. Suramin antagonized ATP (pA2 = 5.52 +/- 0.17, Schild plot slope = 0.67 +/- 0.08) and 2-methylthio-ATP (pA2 = 5.78 +/- 0.30, Schild plot slope = 1.37 +/- 0.39) while responses to 5'-N-ethylcarboxamidoadenosine (NECA) were unaffected. The findings suggest that suramin, while it is selective for P2 relative to P1 purinoceptors, is not a true competitive antagonist. Pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS) antagonized ATP in isolated guinea-pig vas deferens, but had no effect on responses to ATP in guinea-pig taenia caeci indicating it is selective for P2X relative to P2Y purinoceptors.
authors.affiliation: Smooth Muscle Pharmacology Group, School of Biological Sciences, University of Manchester, UK.
authors.forename: A S
authors.initials: AS
authors.lastname: Piper
authors.forename: M
authors.initials: M
authors.lastname: Hollingsworth
mesh_terms: D000241:Adenosine / Q000037:antagonists & inhibitors; D000818:Animals; D002432:Cecum / Q000378:metabolism; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000378:metabolism*; D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D011732:Pyridoxal Phosphate / Q000031:analogs & derivatives / Q000494:pharmacology; D011983:Receptors, Purinergic / Q000187:drug effects*; D013498:Suramin / Q000494:pharmacology; D013806:Theophylline / Q000031:analogs & derivatives / Q000494:pharmacology
chemical_list: D058906:Purinergic P1 Receptor Agonists; D058915:Purinergic P1 Receptor Antagonists; D058910:Purinergic P2 Receptor Agonists; D058919:Purinergic P2 Receptor Antagonists; D011983:Receptors, Purinergic; C077792:pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid; D011732:Pyridoxal Phosphate; D013498:Suramin; C031433:8-(4-sulfophenyl)theophylline; D013806:Theophylline; D000241:Adenosine