The Blood of Carnivorous Marsupials: Low Hemoglobin Oxygen Affinity

Abstract

We examined the blood of four dasyurid marsupials, all small, active insectivores and/or carnivores, to establish if there were any specializations in oxygen transport. All four species had hemoglobins with a low affinity for oxygen. This was demonstrated by high P50's (the partialpressure of oxygen [PO₂] at which the hemoglobin is half-saturated with oxygen) of the whole blood (means of 38.3-59.8 mmHg) and of red cells suspended in a physiological buffer (means of 41.6-49.0 mmHg) at a CO₂ tension of 43 mmHg. There was a strong correlation betuween increase in body mass over three orders of magnitude and increase in the oxygen affinity of the whole blood. The effects of changing CO₂ tensions on the oxygen affinity of whole blood were measured as △log P50/Δlog PCO₂; mean values ranged from 0.25 to 0.373. Values for △log P50/ΔpH wuere measured for red-cell suspensions; means values ranged from -0.40 to -0.481. The introduction of 2,3-diphosphoglycerate significantly decreased the oxygen affinity, of the hemoglobin of Dasyuroides byrnei. The blood of D. byrnei and Dasyurus viverrinus had high hematocrits and high concentrations of hemoglobin. We conclude that hemoglobins with a low affinity for oxygen, an adaptation to an active lifestyle, are a characteristic of dasyurid marsupials generally.