The interaction between O-2 and CO2 exchange in rainbow trout during graded sustained exercise

A quantitative analysis of O-2 and CO2 transport was conducted in resting a nd exercising rainbow trout. and these data were used to quantify the magni tude of coupling between O-2 and CO2 exchange, in vivo. The release of Bohr protons during haemoglobin-oxygenation was non-linear over the Hb-O-2 equi librium curve used in trout subjected to different levels of sustained exer cise. At low swimming speeds, when venous blood O-2 content (Cv(O2)) was hi gh, there was a small acidosis as blood passed through the gills, indicatin g more protons were released during oxygenation of Hb than were consumed du ring HCO3- dehydration. At higher swimming speeds, when Cv(O2) was low, the re was a significant alkalosis in arterial relative to venous blood, indica ting that fewer protons were released upon oxygenation than HCO3- ions were dehydrated to CO2. Haldane coefficients (moles of protons released per mol e of O-2 which binds to Hb), calculated from steady state arterial and mixe d-venous parameters. revealed that under resting conditions all blood CO2 r emoved from the blood during gill transit was stoichiometrically related to O-2 uptake through the release of Bohr protons during Hb oxygenation. The magnitude of coupling between CO, excretion and O-2 uptake decreased from 1 00% to less than 40% at the maximal swimming velocity when the largest regi on of the Hb-O-2 equilibrium curve was used for gas exchange. The non-linea r release of Bohr protons over the range of Hb-O-2 saturation in the blood reduces HCO3- dehydration at the gills during greater work loads elevating arterial P-CO2 levels, leading to an increase in HCO3- buffer capacity of t he blood and tissues. (C) 2000 Elsevier Science B.V. All rights reserved.