Buffering characteristics of eel blood at the extreme conditions in the swimbladder

CO₂ binding in whole blood and true plasma of the eel was estimated by measuring CO₂ content and pH in blood aliquots equilibrated with various P_CO2 values over a wide range expected to occur in the swimbladder. Bicarbonate concentration, HCO₃⁻], was calculated using the CO₂ solubility coefficient, which was measured to average 50 μmol·L⁻¹·Torr⁻¹ (20°C). Buffer lines of non-bicarbonate buffers were obtained in plots of HCPO₃⁻] against pH, and non-bicarbonate buffer values, β_NB, were obtained by curve. fitting.In the pH range 6.6–8.2, the buffer line for oxygenated whole blood was sigmoid, while that for deoxygenated blood increased its slope monotonously with increasing pH. The β_NB for oxygenated blood displayed a maximum of about 8.6 mmol·L⁻¹pH⁻¹ at pH = 7.4 and dropped down to below 1 mmol·L⁻¹·pH⁻¹ at higher and lower pH. Similar shapes of the buffer lines were obtaned in true plasma; the HCO₃⁻] levels and β_NB values were, however, somewhat higher than in whole blood.These data are useful fo assess the back-diffusion of CO₂ and HCO₃⁻ in the rete mirabile of the fish swimbladder and to estimate the effects CO₂ back-diffusion exerts on the counter-current enhancement of O₂ in the rete.