Comparison of hematological traits and oxygenation properties of hemoglobins from highland and lowland Asiatic toad (Bufo gargarizans).

The Asiatic toad (Bufo gargarizans) belonging to the family of Bufonidae (Anura: Amphibia) is successfully residing on the Qinghai-Tibetan Plateau (QTP). To investigate whether the oxygen delivery undergoes adaptive adjustments to high-altitude environments in Asian toads inhabiting the QTP (Zoige County, 3446 m), choosing low-altitude populations (Chengdu City, 500 m) as control, we measured hematological traits, O2 affinities of whole blood, Hb-O2 affinities of purified Hbs, their sensitivities to temperature, and allosteric effectors (H+, Cl- and ATP). Our results showed that high-altitude Asiatic toads possessed significantly increased hemoglobin concentration, hematocrit, and red blood cell count, but significantly decreased erythrocyte volume compared with low-altitude toads. The whole blood and purified Hbs of high-altitude Asiatic toads both exhibited significantly higher O2 affinities compared with low-altitude toads. Substantially increased intrinsic Hb-O2 affinities of high-altitude Asiatic toads Hbs are likely to be the main reason for its elevated Hb-O2 affinities given the anionic cofactor sensitivities of high- and low-altitude toads were similar. The Hbs of high-altitude toads were also characterized by distinctly strong Bohr effects at the low temperature and low-temperature sensitivities. The adaptive adjustments of hematological traits could enhance the blood-O2 carrying capacity of high-altitude Asiatic toads. The increased Hb-O2 affinities could safeguard the pulmonary O2 uploading under hypoxia. The strong Bohr effects at the low temperature could help the release of O2 in metabolic tissues and cold limbs, while low-temperature sensitivity could minimize the effect of temperature fluctuation on the Hb-O2 affinity.