Freshwater turtles, and specifically, painted turtles, Chrysemys picta, are
the most anoxia-tolerant air-breathing vertebrates. These animals can surv
ive experimental anoxic submergences lasting up to 5 months at 3 degrees C.
Two general integrative adaptations underlie this remarkable capacity. Fir
st is a profound reduction in energy metabolism to approximate to 10% of th
e normoxic rate at the same temperature. This is a coordinated reduction of
both ATP generating mechanisms and ATP consuming pathways of the cells. Se
cond is a defense of acid-base state in response to the extreme lactic acid
osis that results from anaerobic glycolysis. Central to this defense is an
exploitation of buffer reserves within the skeleton and, in particular, the
turtle's shell, its most characteristic structure. Carbonates are released
from bone and shell to enhance body fluid buffering of lactic acid and lac
tic acid moves into shell and bone where it is buffered and stored. The com
bination of slow metabolic rate and a large and responsive mineral reserve
are key to this animal's extraordinary anaerobic capacity. (C) 2000 Elsevie
r Science Inc. All rights reserved.