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

Whole blood oxygen equilibrium curves (O2EC's) and related hematologic properties are reported for the turtle Chrysemys picta exposed to two experimental conditions. Summer turtles were maintained at 24 degrees C with free access to air; winter turtles were submerged for 4-12 wk in N2-bubbled water at 3 degrees C. Half-saturation Po2's at 3 degrees C for blood from summer and winter animals were 4.1 and 4.5 Torr, respectively. At 24 degrees C, summer and winter P50's were 20.2 and 22.7 Torr, respectively. The winter turtle P50 values were lower than predicted since prolonged submergence effected a severe metabolic acidosis; 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 O2EC shape. Winter turtle curves exhibited high O2 affinity below P50 while they were distinctly right-shifted above 50% S. Winter animals also exhibited reduced CO2-Bohr coefficients (delta log Po2/delta pH) at 3 and 24 degrees C. Prolonged submergence did not affect the animal's isohemoglobin profile (demonstrated 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 O2EC position and shape may result from reduction in RBC organic phosphates. Furthermore, these observed changes in blood oxygen transport may facilitate O2 loading during winter submergence via extrapulmonary gas exchange.