title: High affinity and temperature sensitivity of blood oxygen binding in Pangasianodon hypophthalmus due to lack of chloride-hemoglobin allosteric interaction.
abstract: Air-breathing fishes represent interesting organisms in terms of understanding the physiological changes associated with the terrestrialization of vertebrates, and, further, are of great socio-economic importance for aquaculture in Southeast Asia. To understand how environmental factors, such as high temperature, affect O2 transport in air-breathing fishes, this study assessed the effects of temperature on O2 binding of blood and Hb in the economically important air-breathing fish Pangasianodon hypophthalmus. To determine blood O2 binding properties, blood was drawn from resting cannulated fishes and O2 binding curves made at 25°C and 35°C. To determine the allosteric regulation and thermodynamics of Hb O2 binding, Hb was purified, and O2 equilibria were recorded at five temperatures in the absence and presence of ATP and Cl(-). Whole blood had a high O2 affinity (O2 tension at half saturation P50 = 4.6 mmHg at extracellular pH 7.6 and 25°C), a high temperature sensitivity of O2 binding (apparent heat of oxygenation ΔH(app) = -28.3 kcal/mol), and lacked a Root effect. Further, the data on Hb revealed weak ATP binding and a complete lack of Cl(-) binding to Hb, which, in part, explains the high O2 affinity and high temperature sensitivity of blood O2 binding. This study demonstrates how a potent mechanism for increasing O2 affinity is linked to increased temperature sensitivity of O2 transport and provides a basic framework for a better understanding of how hypoxia-adapted species will react to increasing temperatures.
authors: Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark; cdamsg@gmail.com.
authors: Christian
authors: C
authors: Damsgaard
authors: Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark; College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam.
authors: Le My
authors: le M
authors: Phuong
authors: College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Vietnam.
authors: Do Thi Thanh
authors: do TT
authors: Huong
authors: Department of Biology, University of Southern Denmark, Odense, Denmark; and.
authors: Frank B
authors: FB
authors: Jensen
authors: Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark;
authors: Tobias
authors: T
authors: Wang
authors: Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark;
authors: Mark
authors: M
authors: Bayley
mesh_terms: D000222:Adaptation, Physiological; D000255:Adenosine Triphosphate / Q000097:blood; D000818:Animals; D001784:Blood Gas Analysis; D002397:Catfishes / Q000097:blood*; D002712:Chlorides / Q000097:blood*; D004912:Erythrocytes / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism*; D006863:Hydrogen-Ion Concentration; D008365:Manometry; D008954:Models, Biological; D010100:Oxygen / Q000097:blood*; D010108:Oxyhemoglobins / Q000378:metabolism; D011485:Protein Binding; D012119:Respiration; D013696:Temperature
chemical_list: D002712:Chlorides; D006454:Hemoglobins; D010108:Oxyhemoglobins; D000255:Adenosine Triphosphate; D010100:Oxygen
keywords: ATP; allostery; chloride; oxygen affinity; pangasius