Oxygen transfer kinetics of red blood cells of the turtle Pseudemys scripta elegans

The kinetics of O2 uptake into, and release from, the red blood cells (RBC) of the turtle Pseudemys scripta elegans were determined with a stopped-flow technique at varied temperature (10-30 degrees C) and pH (7.5-7.9). The results were compared to those obtained for RBC of other vertebrates and related to morphometric and physiological data on gas/blood diffusion in turtle lungs. The O2 transfer conductance of RBC, G, for O2 release into high concentrations of dithionite, considered to represent the best estimate of true RBC transfer conductance for O2 uptake and release, averaged 0.17 +/- 0.01 at 30 degrees C, 0.13 +/- 0.01 at 20 degrees C, 0.09 +/- 0.01 at 10 degrees C (mean +/- SD, in mmol.min-1.Torr-1.(mlRBC)-1). These values are about one half the corresponding value for human RBC, and this difference may be due to the larger size of turtle RBC (volume, 327 microns 3) compared to human RBC (90 microns 3). The temperature dependence of G, Q10 = 1.3 indicates that, as in human RBC, diffusion through aqueous media is the main limiting factor for O2 exchange. Morphometric data on the lungs of Pseudemys scripta suggest that the resistance to O2 transfer by RBC is lower than that offered by the gas-blood barrier. The total apparent transfer resistance to CO, obtained from previous measurements of pulmonary diffusing capacity for CO in the same species, is much higher than that predicted from the combination of RBC O2 kinetics and morphometric data on gas-blood barrier.