O2 binding and CO2 sensitivity in hemoglobins of subterranean African mole rats

Inhabiting deep and sealed subterranean burrows, mole rats exhibit a remarkable suite of specializations, including eusociality (living in colonies with single breeding queens), extraordinary longevity, cancer immunity and poikilothermy, and extreme tolerance of hypoxia and hypercapnia.With little information available on adjustments in hemoglobin (Hb) function that may mitigate the impact of exogenous and endogenous constraints on the uptake and internal transport of O2, we measured hematological characteristics, as well as Hb-O2 binding affinities and their sensitivities to pH (Bohr effect), CO2, temperature and 2,3 diphosphoglycerate (DPG, the major allosteric modulator of Hb-O2 affinity in the red cells) in four social and two solitary species of African mole rats (family Bathyergidae) originating from different biomes and soil types across Central and Southern Africa. We find no consistent patterns in hematocrit (Hct) and blood and red cell DPG and Hb concentrations or in intrinsic Hb-O2 affinity and its sensitivity to pH and DPG that correlate with burrowing, sociality and soil-type. However, the results reveal low specific (pH-independent) effects of CO2 on Hb-O2 affinity compared to humans that predictably safeguard pulmonary loading under hypoxic and hypercapnic burrow conditions. The O2-binding characteristics are discussed in relation to available information on the primary structure of Hbs from adult and developmental stages of mammals subjected to hypoxia and hypercapnia and the molecular mechanisms underlying functional variation in rodent Hbs.