Possible adaptive significance of low red cell organic phosphates in crocodiles

Abstract

Abstract At similar conditions of temperature and P CO2 whole blood oxygen affinity of C. porosus is similar to that of its hemolysate as measured by other authors. Like other crocodilians so far measured, C. porosus , C. novaeguinea and C. johnstoni have low levels of red cell organic phosphates. A major role of CO 2 in determination of oxygen affinity has been described previously for hemolysates of C. porosus and we confirm this in whole blood. Interestingly, however, O 2 affinity may be less sensitive to pH. Low oxygen affinity, insensitivity of O 2 affinity to organic phosphates, and low levels of red cell organic phosphates are features that C. porosus shares with mammals having low red cell 2,3‐DPG. These mammals share with C. porosus a capability for shortlived bursts rather than sustained activity. At low levels of organic phosphate it is known for human blood that the fixed‐acid Bohr effect is much reduced. We propose that lowering red cell organic phosphates may be an adaptive strategy to reduce the fixed acid Bohr‐effect in animals subject to large changes in plasma pH. Such changes may be associated with a prolonged dive or other behavioural event which depends on anaerobic glycolysis.