title: Pardaxin produces postjunctional muscle contraction in guinea-pig intestinal smooth muscle.
abstract: The action of pardaxin (PX), a toxin isolated from the secretion of the Red Sea flatfish, Pardachirus marmoratus, was studied on longitudinal muscle of guinea-pig ileum. Pardaxin contracted the ileum and subsequently abolished muscle contraction to 5-hydroxytryptamine (5-HT), but did not affect the responses to acetylcholine (ACh) and substance P(SP). Pardaxin-induced contraction was only partially suppressed by atropine and not affected by tetrodotoxin or morphine. Preparations desensitized to 5-HT or SP responded normally to pardaxin. Pardaxin-induced contractions were normal in K+-depolarizing Krebs Ringer solution and not affected by black widow spider venom. It is concluded that the pardaxin-induced muscle contractions are not mediated through the release of neurotransmitters and do not involve 5-HT, SP or ACh receptors, but are due to a direct action on the muscle contractile mechanism.
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D004155:Diphenhydramine / Q000494:pharmacology; D004347:Drug Interactions; D004558:Electric Stimulation; D005397:Fish Venoms / Q000494:pharmacology*; D006168:Guinea Pigs; D066298:In Vitro Techniques; D007537:Isometric Contraction; D009020:Morphine / Q000494:pharmacology; D009119:Muscle Contraction / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects*; D009538:Nicotine / Q000494:pharmacology; D010830:Physostigmine / Q000494:pharmacology; D012701:Serotonin / Q000494:pharmacology; D013111:Spider Venoms / Q000494:pharmacology; D013373:Substance P / Q000494:pharmacology
chemical_list: D005397:Fish Venoms; D013111:Spider Venoms; D012701:Serotonin; D013373:Substance P; C017603:pardaxin; D009538:Nicotine; D009020:Morphine; D004155:Diphenhydramine; D010830:Physostigmine; D000109:Acetylcholine; C038599:black widow spider venom