Respiratory properties of blood in a strictly aquatic and predominantly skin-breathing urodele, Cryptobranchus alleganiensis.

The strictly aquatic urodele. Cryptobranchus alleganiensis, is one of the largest gill-less vertebrates in which most of the respiratory gas exchanges occur across the skin. In this study we have examined some of the gas carrying relationships in blood to determine whether certain properties are particularly adaptive to the hellbender's well oxygenated habitat and predominantly cutaneous mode of respiration. The O2 dissociation curve is sigmoidal (n = 2.9) having a P50 of 23.6 mm Hg (at pHa and PaCO2) and a Bohr factor of -0.24. A considerable amount of arterio-venous mixing prior to the ejection of blood from the heart is thought to account for a comparatively low arterial O2 1-1 .pH-1 for a hematocrit of 29%. Attention is drawn to the variability in the protein buffering related CO2 combining properties in vitro caused by hct alterations during different methods of blood sampling. Acid-base relationships between whole blood, true plasma and separated plasma are essentially the same as those described for mammalian blood. Interspecies comparison with the data from this study suggest that factors such as microhabitat, rather than water or air breathing per se, may influence the characteristics of blood O2 and CO2 carriage in amphibians.