Blood oxygen transport in the house sparrow,Passer domesticus

Abstract

Oxygen equilibrium curves (O2EC's) were generated for the adult house sparrowPasser domesticus at temperatures from 35 to 45 °C using a thin blood film technique (Fig. 1). At in vivo pH (7.47±0.02) and 41 °C, the half-saturationP O 2 was 43.4±0.5 Torr. Cooling the blood from normal body temperature to 35 °C had a greater, effect on O2 affinity (ΔH=−12.3 kcal/mol O2) than warming the blood to 45 °C (−6.2 kcal/mol O2). The CO2 Bohr coefficients (Δlog $$P_{{\text{O}}_{\text{2}} } $$ /Δ pH) atP 50 were similar at 35, 41, and 45 °C (range −0.48 to −0.49). Furthermore, the CO2 Bohr slopes were reasonably saturation independent between 10 and 90% S. Hill plots forPasser blood were nonlinear at each temperature; Hill coefficients (n H ) increased from the 2.5–2.7 range below 40% S to values of 3.3–3.6 above 60% S (Fig. 2). The sparrow equilibrium data at each temperature were accurately fitted by fourth order polynomial equations (Figs. 3, 4). The mean absolute errors in $$P_{{\text{O}}_{\text{2}} } $$ for these empiric expressions were 0.14, 0.09 and 0.33 Torr for O2EC's at 35,41 and 45 °C, respectively. These complex equilibrium curve shapes observed withPasser blood may reflect the presence of multiple hemoglobins; isoelectric focusing techniques revealed two structurally distinct isohemoglobins with a molar ratio of 3.7 (Table 2). The combined effects of the sparrow O2EC, shape (steep upper limb), (Fig. 5), the large ΔH, with blood cooling, and the influence of respiratory alkalosis on oxygen affinity may promote blood-O2 transport at altitude.