AJP - Regulatory, Integrative and Comparative Physiology, Vol 251, Issue 5 901-R908, Copyright © 1986 by American Physiological Society
Oxygen binding in alligator blood related to temperature, diving, and "alkaline tide"
R. E. Weber and F. N. White
Blood of Alligator mississippiensis has a relatively high O2 affinity, the
half-saturation O2 tension (P50) = 24.5 Torr at pH 7.495, the arterial,
normocapnic pH at 25 degrees C. Although the overall temperature
sensitivity of P50 at 15, 25, and 35 degrees C and constant pH is low, the
effect on P50 almost doubles when measured at the in vivo pH of each
temperature (delta Happ = -24 and -47 kJ/mol, respectively). The CO2 Bohr
effect (theta CO2 = -0.95) is 5.5 times greater than the fixed acid Bohr
effect (theta FA), and the Haldane effect is small (approximately 0.03 pH
units). The relatively high O2 affinity may ensure efficient utilization of
the lung O2 reserve during breath holding and diving, whereas its
pronounced in vivo temperature sensitivity may be adaptive to the high
temperature quotients of the organismic O2 requirement. The large
difference between theta CO2 and theta FA will favor constancy in blood O2
affinity in the face of large activity-induced increases in blood lactate
and pronounced feeding-induced alkaloses. These "alkaline tides," which
result from an exchange of plasma Cl- for HCO-3 across the gut wall, appear
to be only slightly compensated by increased blood CO2 tensions. The
results are additionally discussed in terms of allosteric modulation of
hemoglobin-O2 affinity in crocodilians.
