AJP - Regulatory, Integrative and Comparative Physiology, Vol 271, Issue 5 1205-R1211, Copyright © 1996 by American Physiological Society
Signal transduction, second messenger, and protein kinase responses during freezing exposures in wood frogs
C. P. Holden and K. B. Storey
Institute of Biochemistry, Carleton University, Ottawa, Ontario, Canada.
Changes in the percentage of adenosine 3', 5'-cyclic monophosphate
(cAMP)-dependent protein kinase present as the active catalytic subunit
(PKAc) and in the levels of the second messengers cAMP, guanosine
3',5'-cyclic monophosphate (cGMP), and D-myo-inositol 1,4,5-trisphosphate
(IP3) were quantified in tissues of the freeze-tolerant wood frog Rana
sylvatica over the course of freezing at -2.5 degrees C and thawing at 5
degrees C. Freezing exposure rapidly raised liver cAMP concentration and
%PKAc (by 2- and 6-fold, respectively) within 2 min postnucleation; both
peaked and stabilized between 5 and 60 min postnucleation but declined with
longer freezing. Other organs also showed elevated PKAc during freezing,
particularly skeletal muscle. By contrast, cGMP concentration was reduced
in muscle and kidney after 24 h of freezing but rose after thawing in
muscle. Liver also showed a twofold elevation of cGMP during thawing. The
protein kinase C (PKC) second messenger, IP3, rose throughout freezing in
liver, reaching levels 11-fold higher than control values after 24 h of
freezing. IP3 was also elevated in brain after 4 and 8 h of freezing. The
different patterns of cAMP, protein kinase A (PKA), and IP3 changes in
liver suggest that, whereas cAMP and PKA clearly mediate the rapid
activation of glucose output as a cryoprotectant, IP3 and PKC may be
involved instead with metabolic responses that deal with the consequences
of long-term freezing, such as ischemia resistance or cell volume control.
