Blood-gas properties and function in the fossorial mole rat under normal and hypoxic-hypercapnic atmospheric conditions

Abstract

Blood and tissue gas exchange properties of mole rats in normoxic and hypoxic-hypercapnic conditions were compared to the common mammalian pattern. RBC count was 14.0 +/- 1.2-10(6)/microliter. Hb concentration was 15.0 +/- 0.4g/100 ml. P50 (at pH 7.4 and 37 degrees C) was 29.5 +/- 0.5 mm Hg. Oxygen capacity averaged 20.2 +/- 0.4 vol% and the Hill coefficient was 2.9 +/- 0.1. The Bohr effect was -0.53 +/- 0.02 (deltalog P/deltapH). The temperature coefficient was 0.0152 +/- 0.0014 (deltalog P/delta degrees C). The Haldane effect was 4.8 +/- 0.5 (deltaCCO2 vol%)at PCO2 =40 mm Hg. Steady-state partial pressures in gas pockets were PO2 = 15.1 +/- 1.4 mm Hg and PCO2 = 85.8 +/- 3.9 mm Hg in normoxia, and 11.5 +/- 3.0 and 101.8 +/- 3.5 repectively in hypoxia-hypercapnia (PIO2 congruent to 85 mm Hg). Under the same conditions 2,3-DPG dropped from 0.87 and 0.88 to 0.62 and 0.65 (mol/mol Hb) in the rat and in the white rat, respectively. Heart muscle myoglobin concentration of the mole rat (1.44 mg/g) did not differ significantly from that of the white rat (1.96 mg/g), whereas masseter myoglobin was 4.0 mg/g--significantly different from the rat (1.21 mg/g). Results indicate that the strategy used by the mole rat to maintain a normal metabolic rate under variable atmospheric conditions, besides having high oxygen affinity, is to expand the physiological range of the oxygen dissociation curve to very low oxygen tensions, at the expense of its acid-base regulation. The regulation of the shape of the oxygen dissociation curve is discussed.