title: E-ring isoprostane augments cholinergic neurotransmission in bovine trachealis via FP prostanoid receptors.
abstract: Isoprostanes are prostaglandin-like molecules that accumulate in oxidative stress and also exert powerful biological effects on a wide variety of tissues. We investigated the effects of several different isoprostanes on contractions evoked by electrical field stimulation (EFS) in bovine trachealis, finding only 15-E2t-IsoP to augment those responses. Many others have shown that isoprostanes act on prostanoid receptors, usually those of the thromboxane-selective prostanoid receptor (TP) subtype, although some describe actions through prostaglandin E2-selective prostanoid receptor (EP) or less frequently through prostaglandin F2alpha-selective prostanoid receptors (FP). We used an extensive panel of highly selective agonists and antagonists of prostanoid receptors to characterize the ones through which 15-E2t-IsoP was acting here. Pretreatment with the FP-selective AL-8810 significantly inhibited the augmentation, whereas TP- and EP-selective blockers did not. On the other hand, the augmentation exerted by 15-E2t-IsoP was mimicked by submicromolar concentrations of the FP-selective agonists PGF2alpha and fluprostenol, as well as by micromolar concentrations of the TP-selective agonist U46619. The concentration-response relationship for exogenously added acetylcholine was not significantly affected by 15-E2t-IsoP, confirming that the effect of the latter on EFS-evoked responses was exerted prejunctionally (i.e., to enhance release of Ach from nerve endings), rather than a direct postjunctional effect via a receptor on the smooth muscle. Finally, we investigated whether the inhibitory (adrenergic) innervation was also modulated by 15-E2t-IsoP, finding EFS-evoked relaxations to be unaffected by the isoprostane. We conclude that 15-E2t-IsoP acts upon an FP receptor on the cholinergic nerve endings, leading to enhanced neurotransmission.
authors.affiliation: Firestone Institute for Respiratory Health, St. Joseph's Healthcare, and Department of Medicine, McMaster University, Hamilton, Ontario, Canada.
authors.forename: Christine
authors.initials: C
authors.lastname: Paredes
authors.forename: Tracy
authors.initials: T
authors.lastname: Tazzeo
authors.forename: Luke J
authors.initials: LJ
authors.lastname: Janssen
mesh_terms: D000109:Acetylcholine / Q000494:pharmacology; D000818:Animals; D002417:Cattle; D002794:Choline / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D066298:In Vitro Techniques; D028421:Isoprostanes / Q000494:pharmacology*; D018716:Molecular Mimicry / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000166:cytology / Q000187:drug effects; D009474:Neurons / Q000187:drug effects / Q000378:metabolism; D011982:Receptors, Prostaglandin / Q000819:agonists / Q000037:antagonists & inhibitors / Q000378:metabolism*; D017482:Receptors, Thromboxane / Q000819:agonists / Q000037:antagonists & inhibitors; D009435:Synaptic Transmission / Q000187:drug effects*; D014132:Trachea / Q000166:cytology / Q000187:drug effects* / Q000378:metabolism*
chemical_list: D028421:Isoprostanes; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; C034671:prostaglandin F2alpha receptor; D002794:Choline; D000109:Acetylcholine