title: The effects of hypoxic bradycardia and extracellular HCO3(-)/CO2 on hypoxic performance in the eel heart.
abstract: During hypoxia, fishes exhibit a characteristic hypoxic bradycardia, the functional significance of which remains debated. Here, we investigated the hypothesis that hypoxic bradycardia primarily safeguards cardiac performance. In preparations from the European eel (Anguilla anguilla), a decrease in stimulation frequency from 40 to 15 beats min(-1), which replicates hypoxic bradycardia in vivo, vastly improved cardiac performance during hypoxia in vitro. As eels display dramatic shifts in extracellular HCO3(-)/CO2, we further investigated the effect this has upon hypoxic cardiac performance. Elevations from 10 mmol l(-1) HCO3(-)/1% CO2 to 40 mmol l(-1) HCO3(-)/4% CO2 had few effects on performance; however, further, but still physiologically relevant, increases to 70 mmol l(-1) HCO3(-)/7% CO2 compromised hypoxia tolerance. We revealed a four-way interaction between HCO3(-)/CO2, contraction frequency, hypoxia and performance over time, whereby the benefit of hypoxic bradycardia was most prolonged at 10 mmol l(-1) HCO3(-)/1% CO2. Together, our data suggest that hypoxic bradycardia greatly benefits cardiac performance, but its significance may be context specific.
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, Aarhus C 8000, Denmark william.joyce@bios.au.dk.
authors.forename: William
authors.initials: W
authors.lastname: Joyce
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, Aarhus C 8000, Denmark.
authors.forename: Maj
authors.initials: M
authors.lastname: Simonsen
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, Aarhus C 8000, Denmark.
authors.forename: Hans
authors.initials: H
authors.lastname: Gesser
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, Building 1131, Universitetsparken, Aarhus C 8000, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
mesh_terms: D000811:Anguilla / Q000502:physiology*; D000818:Animals; D001639:Bicarbonates / Q000494:pharmacology*; D001919:Bradycardia / Q000503:physiopathology / Q000662:veterinary*; D002245:Carbon Dioxide / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006321:Heart / Q000503:physiopathology; D000860:Hypoxia / Q000503:physiopathology / Q000662:veterinary*; D009200:Myocardial Contraction / Q000187:drug effects*
chemical_list: D001639:Bicarbonates; D002245:Carbon Dioxide
keywords: Anguilla anguilla; Contractility; Heart rate; Myocardial hypoxia