QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online October 21, 2005
Journal of Experimental Biology 208, 4079-4089 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01859

This Article Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in JEB Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Costanzo, J. P. Articles by Lee, R. E. Search for Related Content PubMed PubMed Citation Articles by Costanzo, J. P. Articles by Lee, R. E., Jr Social Bookmarking                         What's this?

Cryoprotection by urea in a terrestrially hibernating frog

Jon P. Costanzo^* and Richard E. Lee, Jr

Department of Zoology, Miami University, Oxford, OH 45056, USA

^* Author for correspondence (e-mail: costanjp{at}muohio.edu)

Accepted 25 August 2005

The role of urea as a balancing osmolyte in osmotic adaptation is well known, but this `waste product' also has myriad other functions in diverse taxa. We report that urea plays an important, previously undocumented role in freezing tolerance of the wood frog (Rana sylvatica), a northern woodland species that hibernates terrestrially in sites where dehydration and freezing may occur. Wood frogs inhabiting an outdoor enclosure accumulated urea to 65 mmol l^-1 in autumn and early winter, when soil moisture was scarce, but subsequently urea levels fell to 2 mmol l^-1 as the availability of environmental water increased. Laboratory experiments showed that hibernating R. sylvatica can accumulate at least 90 mmol l^-1 urea under relatively dry, warm conditions. During experimental freezing, frogs synthesized glucose but did not accumulate additional urea. Nevertheless, the concentrations of urea and glucose in some tissues were similar. We tested urea's efficacy as a cryoprotectant by measuring lysis and lactate dehydrogenase (LDH) leakage in samples of R. sylvatica erythrocytes frozen/thawed in the presence of physiological levels of urea or other osmolytes. In conferring protection against freeze/thaw damage, urea was comparable to glycerol and as good as or better than glucose, cryoprotectants found in freeze-tolerant frogs and other animals. Urea treatment also improved the viability of intact tissues frozen in vitro, as demonstrated by post-thaw measures of metabolic activity and LDH leakage. Collectively, our findings suggest that urea functions both as an osmoprotectant and a cryoprotectant in terrestrially hibernating amphibians.

Key words: amphibian, freeze tolerance, osmolyte, hibernation, Rana sylvatica, wood frog, cryoprotection

CiteULike    Complore    Connotea    Del.icio.us    Digg    Reddit    Technorati    Twitter    What's this?

Related articles in JEB:

UREA PROTECTS FROGS FROM FROST

Yfke van Bergen
JEB 2005 208: i. [Full Text]  

This article has been cited by other articles:

				J. P. Costanzo and R. E. Lee Jr Urea loading enhances freezing survival and postfreeze recovery in a terrestrially hibernating frog J. Exp. Biol., September 15, 2008; 211(18): 2969 - 2975. [Abstract] [Full Text] [PDF]

				Y. van Bergen UREA PROTECTS FROGS FROM FROST J. Exp. Biol., November 1, 2005; 208(21): i - i. [Full Text] [PDF]