title: High blood oxygen affinity in the air-breathing swamp eel Monopterus albus.
abstract: The Asian swamp eel (Monopterus albus, Zuiew 1793) is a facultative air-breathing fish with reduced gills. Previous studies have shown that gas exchange seems to occur across the epithelium of the buccopharyngeal cavity, the esophagus and the integument, resulting in substantial diffusion limitations that must be compensated by adaptations in others steps of the O₂ transport system to secure adequate O₂ delivery to the respiring tissues. We therefore investigated O₂ binding properties of whole blood, stripped hemoglobin (Hb), two major isoHb components and the myoglobin (Mb) from M. albus. Whole blood was sampled using indwelling catheters for blood gas analysis and determination of O₂ equilibrium curves. Hb was purified to assess the effects of endogenous allosteric effectors, and Mb was isolated from heart and skeletal muscle to determine its O₂ binding properties. The blood of M. albus has a high O₂ carrying capacity [hematocrit (Hct) of 42.4±4.5%] and binds O₂ with an unusually high affinity (P₅₀=2.8±0.4mmHg at 27°C and pH7.7), correlating with insensitivity of the Hb to the anionic allosteric effectors that normally decrease Hb-O₂ affinity. In addition, Mb is present at high concentrations in both heart and muscle (5.16±0.99 and 1.08±0.19mg ∙ g wet tissue⁻¹, respectively). We suggest that the high Hct and high blood O₂ affinity serve to overcome the low diffusion capacity in the relatively inefficient respiratory surfaces, while high Hct and Mb concentration aid in increasing the O₂ flux from the blood to the muscles.
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark. Electronic address: cdamsg@gmail.com.
authors.forename: Christian
authors.initials: C
authors.lastname: Damsgaard
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Inge
authors.initials: I
authors.lastname: Findorf
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Signe
authors.initials: S
authors.lastname: Helbo
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Yigit
authors.initials: Y
authors.lastname: Kocagoz
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Rasmus
authors.initials: R
authors.lastname: Buchanan
authors.affiliation: College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam.
authors.forename: Do Thi Thanh
authors.initials: do TT
authors.lastname: Huong
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Roy E
authors.initials: RE
authors.lastname: Weber
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Angela
authors.initials: A
authors.lastname: Fago
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Mark
authors.initials: M
authors.lastname: Bayley
authors.affiliation: Zoophysiology, Department of Bioscience, Aarhus University, 8000 Aarhus C, Denmark.
authors.forename: Tobias
authors.initials: T
authors.lastname: Wang
mesh_terms: D000465:Algorithms; D000494:Allosteric Regulation; D000818:Animals; D017756:Aquaculture; D001692:Biological Transport; D029941:Fish Proteins / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism*; D006400:Hematocrit / Q000662:veterinary; D006454:Hemoglobins / Q000302:isolation & purification / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008954:Models, Biological; D018482:Muscle, Skeletal / Q000378:metabolism; D009206:Myocardium / Q000378:metabolism; D009211:Myoglobin / Q000302:isolation & purification / Q000378:metabolism*; D010100:Oxygen / Q000097:blood* / Q000378:metabolism; D010101:Oxygen Consumption; D020033:Protein Isoforms / Q000097:blood / Q000302:isolation & purification / Q000378:metabolism; D020545:Respiratory Mucosa; D023701:Smegmamorpha / Q000097:blood / Q000502:physiology*; D014744:Vietnam
chemical_list: D029941:Fish Proteins; D006454:Hemoglobins; D009211:Myoglobin; D020033:Protein Isoforms; D010100:Oxygen
keywords: Air-breathing; Blood; Hemoglobin; Myoglobin; Respiration; Swamp eel