AJP - Regulatory, Integrative and Comparative Physiology, Vol 267, Issue 4 1078-R1088, Copyright © 1994 by American Physiological Society
Freeze tolerance in turtles: visual analysis by microscopy and magnetic resonance imaging
B. Rubinsky, J. S. Hong and K. B. Storey
Department of Mechanical Engineering, University of California, Berkely 94720.
Two visual techniques were used to analyze the patterns of natural freezing
and thawing in freeze-tolerant hatchling painted turtles Chrysemys picta
marginata. Directional solidification plus light microscopy of liver,
heart, and skeletal muscle slices was used to compare freezing at -4
degrees C (a survivable temperature in vivo) and -20 degrees C (not
survivable). At -4 degrees C tissues showed large amounts of ice in
expanded extracellular and vascular spaces, occupying 36% (liver) and 61%
(muscle) of total tissue volume. Cells at -4 degrees C were shrunken, but
intracellular water remained; at -20 degrees C, however, cells showed
little evidence of free water. Liver micrographs showed novel spherical
shells of water associated with intracellular particles (apparently
glycogen granules) suggesting that a noncolligative method of cell water
retention was employed. Proton magnetic resonance imaging was used for
noninvasive analysis of freezing and thawing in the intact animal. Images
showed that freezing propagated in a directional manner through the body
with ice formed first in extraorgan spaces (e.g., abdominal cavity, brain
ventricles). However, thawing occurred uniformly throughout the body core,
and organs melted more rapidly than the extraorgan ice surrounding them.
