Oxygen binding by single red blood cells from the red-eared turtle Trachemys scripta

Oxygen-binding properties of single red blood cells from the red-eared turt le Trachemys scripta were measured by microspectrophotometry to describe th e variation in oxygen affinity of red blood cells and to gain insight into the distribution of functionally different hemoglobins among red blood cell s. Methodologically, this study represents the first report on the cell-to- cell variation in oxygen-binding properties based on oxygen-binding curves of single vertebrate red blood cells. The cells differed significantly with respect to oxygen affinity. Mean oxygen pressure at half saturation of the cells in a blood sample was found to be 20.1 +/- 3.3 (SD) Torr. The distri bution of oxygen affinities among red blood cells is unimodal, indicating t hat the two hemoglobins found in turtle blood are not segregated in distinc t cells. Therefore, the functional interaction shown by these hemoglobins i n vitro is likely to take place in vivo. The considerable variation in oxyg en affinity between individual red blood cells calls for its incorporation in models of tissue oxygenation.