Journal of Applied Physiology, Vol 58, Issue 1 193-199, Copyright © 1985 by American Physiological Society
Low P50 in deer mice native to high altitude
L. R. Snyder
Whereas it is widely believed that animals native to high altitude show
lower O2 partial pressures at 50% hemoglobin saturation (P50) than do
related animals native to low altitude, that "fact" has not been well
documented. Consequently, P50 at pH 7.4, PCO2(7.4), the CO2 Bohr effect,
and the buffer slope (delta log PCO2/delta pH) were determined via the
mixing technique in Peromyscus maniculatus native to a range of altitudes
but acclimated to 340 or 3,800 m. PCO2(7.4) and buffer slope were
substantially lower at high altitude. The change in P50(7.4) between
acclimation altitudes was minimal (0.8% increase at 3,800 m), because of
counterbalancing changes in PCO2, 2,3-diphospho-D-glycerate concentration,
and perhaps other factors. At both acclimation altitudes there was a highly
significant negative correlation between P50(7.4) and native altitude.
Since pH in vivo probably increases slightly at high altitude, the data on
P50 corrected to pH 7.4 are probably underestimates of the difference in in
vivo P50 at low vs. high altitude. Hence these results corroborate
theoretical predictions that low P50 is advantageous under severe hypoxic
stress.
