The interaction between O2 and CO2 exchange in rainbow trout during graded sustained exercise

Area of Science:

• Physiology
• Comparative Physiology
• Fish Biology

Background:

• Understanding gas exchange is crucial for aquatic respiration.
• The Bohr effect describes how oxygen binding to hemoglobin is affected by pH and CO2.
• Quantifying the relationship between oxygen and carbon dioxide transport in fish under varying physiological conditions is important.

Purpose of the Study:

• To quantitatively analyze oxygen (O2) and carbon dioxide (CO2) transport in rainbow trout.
• To determine the magnitude of coupling between O2 and CO2 exchange in vivo during rest and exercise.
• To investigate the impact of exercise intensity on the Bohr effect and its implications for gas exchange.

Main Methods:

• Quantitative analysis of O2 and CO2 transport in rainbow trout.
• Measurement of blood parameters during resting and exercising conditions.
• Calculation of Haldane coefficients to assess the relationship between O2 uptake and CO2 excretion.

Main Results:

• The release of Bohr protons during hemoglobin oxygenation is non-linear with exercise.
• At low exercise, a small acidosis was observed, indicating more protons released than consumed.
• At high exercise, alkalosis occurred, with fewer protons released than HCO3- dehydrated, reducing CO2 excretion coupling to <40%.

Conclusions:

• The non-linear Bohr proton release over the hemoglobin-O2 equilibrium curve reduces CO2 excretion efficiency during high workloads.
• This leads to elevated arterial P(CO2) and increased bicarbonate buffer capacity in blood and tissues.
• The coupling between CO2 excretion and O2 uptake is significantly reduced at maximal swimming velocities in rainbow trout.