Solubility of nitrogen and argon in eel whole blood and its relationship to pH

The solubility coefficients (alpha) for the inert gases, nitrogen (N2) and argon (Ar), were measured by mass spectrometry in whole blood of the freshwater-adapted European eel, Anguilla anguilla, at varied pH and at two temperatures, 5 and 15 degrees C. The pH was altered either by varying PCO2 (0.75-75 mmHg; 1 mmHg = 133.3 Pa) or by adding fixed acid (HCl or lactic acid). No dependence of alpha on pH (range 5.5-8.4) or on lactate concentration (range 0.2-25 mmol l-1) was detectable. Average values (+/- S.D.) for alpha (mumol l-1 mmHg-1) were: alpha N2 = 1.25 +/- 0.01, alpha Ar = 2.60 +/- 0.05 at 5 degrees C and alpha N2 = 1.09 +/- 0.03, alpha Ar = 2.12 +/- 0.07 at 15 degrees C. These data yield values for Q10 of 0.87 for nitrogen and 0.82 for argon, and for activation energy, Ea (kJ mol-1 K-1), of -9.2 for nitrogen and -13.4 for argon. The results do not support earlier reports on significant pH dependence of alpha in eel blood and suggest, in contrast, that no fundamental differences exist in respect of inert gas solubility between whole blood of the eel and of other vertebrates.