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Journal of Experimental Biology 130,27-38 (1987)
Published by Company of Biologists 1987

Oxygen and Carbon Dioxide Transport Characteristics of the Blood of the Nile Monitor Lizard (Varanus Niloticus)

JAMES W. HICKS ¹, ATSUSHI ISHIMATSU ², and NORBERT HEISLER ³

¹ Abteilung Physiologie, Max-Planck-Institut für experimentelle Medizin, Göottingen, FRG; Physiological Research Laboratory, Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA, USA
² Abteilung Physiologie, Max-Planck-Institut für experimentelle Medizin, Göottingen, FRG; Nomo Fisheries Station, Nagasaki University, Nomozaki, Nagasaki 851-05, Japan
³ Abteilung Physiologie, Max-Planck-Institut für experimentelle Medizin, Göottingen, FRG

Oxygen and carbon dioxide dissociation curves were constructed for the blood of the Nile monitor lizard, Varanus niloticus, acclimated for 12h at 25 and 35°C. The oxygen affinity of Varanus blood was low when Pco₂ w a s in the range of in vivo values (25°C: P₅₀ = 34.3 at P_COCO2 = 21 mmHg; 35°C: P₅₀ = 46.2 mmHg at P_COCO2 = 35 mmHg; 1 mmHg = 133.3 Pa), and the oxygen dissociation curves were highly sigmoidal (Hill's n = 2.97 at 25°C and 3.40 at 35°C). The position of the O₂ curves was relatively insensitive to temperature change with an apparent enthalpy of oxygenation (H) of -9.2kJ mol^-1. The carbon dioxide dissociation curves were shifted to the right with increasing temperature by decreasing total C_COCO2 at fixed P_COCO2, whereas the state of oxygenation had little effect on total blood CO₂ content. The in vitro buffer value of true plasma ([HCO₃^-]_pl/-pH_pl) rose from 12.0 mequiv pH^-1^-1 at 25°C to 17.5 mequiv pH^-11^-1 at 35°C, reflecting a reversible increase of about 30% in haemoglobin concentration and haematocrit levels during resting conditions in vivo.

Key words: Bohr effect, blood buffer value, CO₂ dissociation curves, Haldane effect, oxygen affinity, oxygenation enthalpy, O₂ dissociation curves, Reptilia, Varanus niloticus

Accepted on March 25, 1987