Oxygen dissociation curves of whole blood from the Egyptian free-tailed bat, Tadarida aegyptiaca E. Geoffroy, using a thin-layer optical cell

Abstract

Tadarida aegyptiaca (mean body mass 13.5 g) is a fast flying insectivorous bat that  hunts in open areas for extended periods, covering extensive distances during its foraging bouts. Whole blood samples taken from the wing arteries were analysed for  2,3-diphosphoglyceric acid, oxygen affinity and pH. The mean oxygen affinity of T. aegyptiaca blood with a P₅₀-value 38.3 mm Hg (5.1 kPa) is lower than that of  similarsized bats but not as low as the P₅₀-values of 48.5 mm Hg (6.4 kPa) in two mice species. This indicates that oxygen affinity of the blood in T. aegyptiaca and other bats is designed to facilitate both effective binding of oxygen with haemoglobin at the alveolar/blood capillary interface and oxygen offloading in the tissues. Haematocrits (54–60 %) and levels of 2,3 DPG (2.36–3.30 mM l^–1) were higher, and blood pH (7.106–7.229) lower, than those reported for terrestrial species of a similar size, but within the range of values reported for other bats. We conclude that adequate delivery of oxygen to tissues with high metabolic demands during flight is facilitated primarily by an elevated haematocrit and a reduced blood pH in response to elevated levels of metabolic by-products such as 2,3-DPG (from the citrate acid cycle) and CO₂ (leading to increased concentrations of H⁺ ions).

Key words: oxygen affinity, haematocrit, 2,3-diphosphoglyceric acid, blood pH.