Oxygen uptake and blood respiratory properties of the caecilian Boulengerula taitanus.

In contrast to amphibians belonging to the orders Urodela and Anura, virtually no data exist on the respiratory physiology of the more primitive Apoda. This study concerns oxygen uptake and hemoglobin function in the caecilan Boulengerula taitanus, an apodan with fossorial habits. The oxygen uptake rate resembles that of other amphibians of similar size. The blood was high O2 capacity (14 vol%) and the erythrocytes are smaller, and the red cell count is greater than in other amphibians. The oxygen affinity of whole blood is high compared to other amphibians (P50 = 28 mm Hg at 25 degrees C and pH 7.6). The oxygen equilibrium curve is sigmoid (n = 1.79) and the Bohr factor is small (deltalog P50/deltapH = - 0.21). In 'stripped' hemoglobin solutions oxygen affinity increases strongly (P50 = 3.3 mm Hg at 25 degrees C and pH 7.6) and the temperature sensitivity is high (apparent deltaH=-19.4 kcal/mole), but the ATP and pH influences are too low to account for the difference in P50 compared to whole blood. The high oxygen capacity and oxygen affinity and the low Bohr factor may have adaptive significance to this fossorial amphibian.