Respiratory properties of the blood of Crocodylus porosus.

The blood of Crocodylus porosus has a high oxygen capacity (5.5 mmol . 1-1 at hematocrit = 28%). The shape of the oxygen equilibrium curve of the blood is described by 'n' = 2.7 in the physiological range of PCO2, and its oxygen affinity is described by the equation: log10P50 = 0.4163 + 0.0200 T degrees C + 0.3763 log10PCO2. Thus, the blood has a low oxygen affinity which is strongly sensitive to both temperature and PCO2. There is a high buffering capacity, 37 mmol . (1 . pH)-1, and a large Haldane effect, 0.93 mmol CO2 (mmol Hb)-1. The fixed-acid Bohr effect seems to be much reduced in comparison to the CO2-specific Bohr effect. We discuss the possibility that low levels of red cell organic phosphate may be an adaptive strategy to desensitise P50 to changes in plasma pH. The significance of the blood respiratory properties is discussed in terms of the life style of C. porosus, particularly in relation to ectothermy and diving.