title: Glucose uptake and metabolism by red blood cells from fish with different extracellular glucose levels.
abstract: The aim of the present study was to assess whether mechanisms of glucose trafficking by red blood cells (RBCs) relate to species-specific extracellular glucose levels. Atlantic cod (Gadus morhua), Atlantic salmon (Salmo salar), cunner (Tautogolabrus adspersus) and short-horned sculpin (Myoxocephalus scorpius) had plasma glucose levels of 4, 4.1, 1.95 and 0.73 mmol l(-1), respectively. Glucose uptake by isolated RBCs was measured by the initial incorporation of [6-(14)C]-glucose and steady-state glucose metabolism was determined by the production of (3)H(2)O from [2-(3)H]-glucose. Saturation kinetics of glucose uptake and inhibition of both glucose uptake and metabolism by cytochalasin B and phloretin revealed that Atlantic cod, cunner and sculpin RBCs all had a facilitated transport component to glucose trafficking. RBCs from Atlantic salmon showed a linear relationship between glucose uptake and extracellular glucose level, but exhibited clear inhibition of glucose metabolism by cytochalasin B and phloretin, suggesting a component of facilitated glucose transport that is more elusive to detect. The production of (3)H(2)O was linear for at least 6 h and as such presents a rigorous approach to measuring glycolytic rate. Steady-state rates of glucose metabolism were achieved at extracellular levels of approximately 1 mmol l(-1) glucose for RBCs from all species, showing that within-species normal extracellular glucose level is not a primary determinant of the basal level of glycolysis. At physiological levels of extracellular glucose, the ratio of initial glucose uptake to glucose metabolism was 1.5 to 4 for all RBCs, suggesting that there is scope to increase metabolic rate without alteration of the basal glucose uptake capacity.
authors.affiliation: Department of Ocean Sciences, Ocean Sciences Centre, Memorial University of Newfoundland, St John's, NL, Canada, A1C 5S7. wdriedzic@mun.ca
authors.forename: William R
authors.initials: WR
authors.lastname: Driedzic
authors.forename: Kathy A
authors.initials: KA
authors.lastname: Clow
authors.forename: Connie E
authors.initials: CE
authors.lastname: Short
mesh_terms: D000818:Animals; D001692:Biological Transport; D001786:Blood Glucose / Q000378:metabolism; D003571:Cytochalasin B / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D029941:Fish Proteins / Q000378:metabolism; D048389:Gadus morhua / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D010473:Perciformes / Q000378:metabolism*; D010693:Phloretin / Q000378:metabolism; D020317:Salmo salar / Q000378:metabolism*
chemical_list: D001786:Blood Glucose; D029941:Fish Proteins; D003571:Cytochalasin B; D005947:Glucose; D010693:Phloretin