Effect of chronic cold and submergence on blood oxygen transport in the turtle, chrysemys picta

Whole blood oxygen equilibrium curves (O 2EC's) and related hematologic properties are reported for the turtle Chrysemys picta exposed to two experimental conditions. Summer turtles were maintained at 24°C with free access to air; winter turtles were submerged for 4–12 wk in N 2-bubbled water at 3°C. Half-saturation P O 2 's at 3°C for blood from summer and winter animals were 4.1 and 4.5 Torr, respectively. At 24°C, summerand winter P 50's were 20.2 and 22.7 Torr, respectively. The winter turtle P 50 values were lower than predicted since prolonged submergence effected a severe metabolic acidos; blood pH's for winter turtles were 0.65 pH unit lower than for summer animals at both temperatures. Cold submergence also had a profound influence on O 2EC shape. Winter turtle curves exhibited high O 2 affinity below P 50 while they were distinctly right-shifted above 50% S. Winter animals also exhibited reduced CO 2-Bohr coefficients (Δlog P O 2 /ΔpH) at 3 and 24°C. Prolonged submergence did not affect the animal's isohemoglobin profile (demontrated by isoelectric focusing) or [metHb]. The [ATP] and [DPG] in winter turtle red cells, however, decreased significantly; the ratio of organic phosphate ([ATP]+[DPG]) to Hb tetramer fell from 1.4 in summer animals to 0.5 in winter turtles. These findings suggest that the effect of chronic cold and prolonged submergence on turtle O 2EC position and shape may result from reduction in RBC organic phosphates. Furthermore, these observed changes in blood oxygen transport may facilitate O 2 loading during winter submergence via extrapulmonary gas exchange.