Effect of haemoglobin oxygenation on Bohr proton release and CO2 excretion in the rainbow trout.

CO2 excretion in trout is dependent upon the Haldane effect and the release of protons (Bohr protons) from haemoglobin during oxygenation of the blood. Oxygenation of whole blood from trout in vitro, resulted in a non-linear release of Bohr protons over the haemoglobin-oxygen (Hb-O2) equilibrium curve, where the majority of Bohr protons were released between 60 and 100% of Hb oxygen saturation (SO2). Oxygenation of the blood over this region of the Hb-O2 equilibrium curve elevated the HCO3- flux rate across the HCO3-/CI- exchanger on the red cell membrane by about 30% during CO2 excretion in vitro. Oxygenation of the Hb between 0 and 60% SO2 did not elevate CO2 excretion rate in vitro. These data indicate that utilization of different regions of the Hb-O2 dissociation curve in trout in vivo will influence CO2 excretion by altering the rate of HCO3- entry into the red cell during gill blood transit.