title: Hypoxia induces hypersensitivity and hyperreactivity to thromboxane receptor agonist in neonatal pulmonary arterial myocytes.
abstract: PPHN, caused by perinatal hypoxia or inflammation, is characterized by an increased thromboxane-prostacyclin ratio and pulmonary vasoconstriction. We examined effects of hypoxia on myocyte thromboxane responsiveness. Myocytes from 3rd-6th generation pulmonary arteries of newborn piglets were grown to confluence and synchronized in contractile phenotype by serum deprivation. On the final 3 days of culture, myocytes were exposed to 10% O2 for 3 days; control myocytes from normoxic piglets were cultured in 21% O2. PPHN was induced in newborn piglets by 3-day hypoxic exposure (Fi(O2) 0.10); pulmonary arterial myocytes from these animals were maintained in normoxia. Ca2+ mobilization to thromboxane mimetic U-46619 and ATP was quantified using fura-2 AM. Three-day hypoxic exposure in vitro results in increased basal [Ca2+]i, faster and heightened peak Ca2+ response, and decreased U-46619 EC50. These functional changes persist in myocytes exposed to hypoxia in vivo but cultured in 21% O2. Blockade of Ca2+ entry and store refilling do not alter peak U-46619 Ca2+ responses in hypoxic or normoxic myocytes. Blockade of ryanodine-sensitive or IP3-gated intracellular Ca2+ channels inhibits hypoxic augmentation of peak U-46619 response. Ca2+ response to ryanodine alone is undetectable; ATP-induced Ca2+ mobilization is unaltered by hypoxia, suggesting no independent increase in ryanodine-sensitive or IP3-linked intracellular Ca2+ pool mobilization. We conclude hypoxia has a priming effect on neonatal pulmonary arterial myocytes, resulting in increased resting Ca2+, thromboxane hypersensitivity, and hyperreactivity. We postulate that hypoxia increases agonist-induced TP-R-linked IP3 pathway activation. Myocyte thromboxane hyperresponsiveness persists in culture after removal from the initiating hypoxic stimulus, suggesting altered gene expression.
authors.affiliation: Department of Physiology, University of Manitoba, and Biology of Breathing Group, Manitoba Institute of Child Health, Winnipeg, Canada R3A 1R9.
authors.forename: M
authors.initials: M
authors.lastname: Hinton
authors.forename: L
authors.initials: L
authors.lastname: Mellow
authors.forename: A J
authors.initials: AJ
authors.lastname: Halayko
authors.forename: A
authors.initials: A
authors.lastname: Gutsol
authors.forename: S
authors.initials: S
authors.lastname: Dakshinamurti
mesh_terms: D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid / Q000494:pharmacology; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism; D002121:Calcium Channel Blockers / Q000494:pharmacology; D002478:Cells, Cultured; D004195:Disease Models, Animal; D006352:Heart Ventricles / Q000033:anatomy & histology / Q000473:pathology; D006801:Humans; D000860:Hypoxia / Q000503:physiopathology*; D007231:Infant, Newborn; D047028:Macrocyclic Compounds; D032342:Muscle Cells / Q000187:drug effects*; D009543:Nifedipine / Q000494:pharmacology; D009929:Organ Size; D010080:Oxazoles / Q000494:pharmacology; D010547:Persistent Fetal Circulation Syndrome / Q000503:physiopathology*; D011651:Pulmonary Artery / Q000166:cytology / Q000187:drug effects; D017482:Receptors, Thromboxane / Q000819:agonists*; D012433:Ryanodine / Q000494:pharmacology; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects*
chemical_list: D002121:Calcium Channel Blockers; D047028:Macrocyclic Compounds; D010080:Oxazoles; D017482:Receptors, Thromboxane; C108644:xestospongin A; D012433:Ryanodine; D019796:15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5,13-dienoic Acid; D009543:Nifedipine; D002118:Calcium