Effects of hibernation on blood oxygen transport in the golden-mantled ground squirrel.

Isocapnic O2 equilibrium curves (O2EC) were generated for winter hibernating and summer active ground squirrels (Spermophilus lateralis) at 7 degrees and 37 degrees C using thin blood film techniques. Half-saturation PO2 at 7 degrees C and pHa 7.46 were 5.8 +/- 0.1 and 6.9 +/- 0.2 Torr for hibernating and summer squirrels, respectively; P50 values at 37 degrees C and pHa 7.49 were 15.3 +/- 0.1 and 18.1 +/- 0.5 Torr, respectively. This increased blood O2 affinity in the winter animal results, in part, from reductions of RBC organic phosphates. The molar ratio ([ATP] + [DPG])/[Hb4] decreased from 1.55 in summer squirrels to 0.91 in winter hibernators. O2EC shape and CO2 Bohr effect were similar for the two animal groups, but varied with blood temperature. At 7 degrees C, Hill plots were nonlinear; Hill's n increased from values of 2.2-2.4 below 40% S to 2.7-2.9 above 60% S. At 37 degrees C, Hill plots were reasonably linear (n = 2.5). CO2 Bohr slopes (delta log P50/delta pH) for hibernating and euthermic squirrels were -0.37 +/- 0.02 and -0.40 +/- 0.03 at 7 degrees C, respectively, and -0.62 +/- 0.04 and -0.60 +/- 0.02 at 37 degrees C, respectively. Blood O2 capacity was significantly greater (P < 0.001) in the hibernator; hematocrit (55%) and [Hb] (19.1 g/dl) exceeded the summer squirrel values by 20% and 25%, respectively. Estimated PvO2 values for summer and winter animals at 7 degrees C and pH 7.46 were 7.25 and 6.94 Torr, respectively. This suggests that the effect of increased Hb-O2 affinity on PvO2 is offset by increased circulating [Hb]. We conclude that seasonal changes in the O2 transport properties of squirrel blood do not contribute to the depression of aerobic metabolism during winter hibernation.