title: Evidence for a role of heme oxygenase-1 in the control of cardiac function in zebrafish (Danio rerio) larvae exposed to hypoxia.
abstract: Carbon monoxide (CO) is a gaseous neurotransmitter produced from the breakdown of heme via heme oxygenase-1 (HO-1; hypoxia-inducible isoform) and heme oxygenase-2 (HO-2; constitutively expressed isoform). In mammals, CO is involved in modulating cardiac function. The role of the HO-1/CO system in the control of heart function in fish, however, is unknown and investigating its physiological function in lower vertebrates will provide a better understanding of the evolution of this regulatory mechanism. We explored the role of the HO-1/CO system in larval zebrafish (Danio rerio) in vivo by investigating the impact of translational gene knockdown of HO-1 on cardiac function. Immunohistochemistry revealed the presence of HO-1 in the pacemaker cells of the heart at 4 days post-fertilization and thus the potential for CO production at these sites. Sham-treated zebrafish larvae (experiencing normal levels of HO-1) significantly increased heart rate (fH) when exposed to hypoxia (PwO2 =30 mmHg). Zebrafish larvae lacking HO-1 expression after morpholino knockdown (morphants) exhibited significantly higher fH under normoxic (but not hypoxic) conditions when compared with sham-treaded fish. The increased fH in HO-1 morphants was rescued (fH was restored to control levels) after treatment of larvae with a CO-releasing molecule (40 µmol l(-1) CORM). The HO-1-deficient larvae developed significantly larger ventricles and when exposed to hypoxia they displayed higher cardiac output ([Formula: see text]) and stroke volume (SV). These results suggest that under hypoxic conditions, HO-1 regulates [Formula: see text] and SV presumably via the production of CO. Overall, this study provides a better understanding of the role of the HO-1/CO system in controlling heart function in lower vertebrates. We demonstrate for the first time the ability for CO to be produced in presumptive pacemaker cells of the heart where it plays an inhibitory role in setting the resting cardiac frequency.
authors.affiliation: Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5 vtzan032@uottawa.ca.
authors.forename: Velislava
authors.initials: V
authors.lastname: Tzaneva
authors.affiliation: Department of Biology, University of Ottawa, 30 Marie Curie, Ottawa, ON, Canada K1N 6N5.
authors.forename: Steve F
authors.initials: SF
authors.lastname: Perry
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002302:Cardiac Output; D003971:Diastole / Q000187:drug effects; D055785:Gene Knockdown Techniques; D006321:Heart / Q000187:drug effects / Q000503:physiopathology*; D006339:Heart Rate / Q000502:physiology; D051547:Heme Oxygenase-1 / Q000378:metabolism*; D000860:Hypoxia / Q000201:enzymology* / Q000503:physiopathology*; D007814:Larva / Q000166:cytology / Q000187:drug effects / Q000502:physiology; D060172:Morpholinos / Q000494:pharmacology; D009929:Organ Size / Q000187:drug effects; D015203:Reproducibility of Results; D013318:Stroke Volume / Q000187:drug effects; D013599:Systole / Q000187:drug effects; D015027:Zebrafish / Q000502:physiology*; D029961:Zebrafish Proteins / Q000378:metabolism*
chemical_list: D060172:Morpholinos; D029961:Zebrafish Proteins; D051547:Heme Oxygenase-1; C000605843:heme oxygenase 1, zebrafish
keywords: Carbon monoxide; Heart rate; Heart size; Pacemaker cells