Access

You are not currently logged in.

Access your personal account or get JSTOR access through your library or other institution:

login

Log in to your personal account or through your institution.

If You Use a Screen Reader

This content is available through Read Online (Free) program, which relies on page scans. Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.

Organ Metabolism and Cryoprotectant Synthesis during Freezing in Spring Peepers Pseudacris crucifer

Thomas A. Churchill and Kenneth B. Storey
Copeia
Vol. 1996, No. 3 (Aug. 1, 1996), pp. 517-525
DOI: 10.2307/1447515
Stable URL: http://www.jstor.org/stable/1447515
Page Count: 9
  • Read Online (Free)
  • Download ($12.00)
  • Subscribe ($19.50)
  • Cite this Item
Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Organ Metabolism and Cryoprotectant Synthesis during Freezing in Spring Peepers Pseudacris crucifer
Preview not available

Abstract

The effects of freezing on organ metabolism were monitored over a 36-h time period at -4 C in spring-collected specimens of a freeze-tolerant frog, Pseudacris crucifer. Within 2 min after nucleation, glycogenolysis in liver was activated as indicated by elevated levels of hexose phosphates; and levels of the cryoprotectant, glucose, rose quickly thereafter. Freezing stimulated a 3.3-fold increase in liver glycogen phosphorylase a activity, and a rapid phase of liver glucose production was maintained for at least the first hour of freezing (21 μ mol· g wet mass-1· h-1), followed by a steady rate of glucose increase of about 3 μ mol· gwm-1· h-1. Final liver glucose levels reached 141 μ mol· gwm-1 after 36 h. Changes in the concentrations of hexose phosphates and fructose-1,6-bisphosphate in liver indicated that glucose production was promoted by an inhibitory block on glycolysis at the phosphofructokinase reaction. Other organs accumulated the glucose exported by liver and cryoprotectant accumulation by heart paralleled the rise in liver glucose levels. Liver energetics were not disrupted during early freezing but with prolonged freezing (4-36 h), ATP content fell, ADP and AMP increased, and energy charge, [ATP + ADP/2]/[ATP + ADP + AMP], was reduced from 0.90 in controls to 0.57 after 36 h freezing. Liver metabolism during freezing was supported by fermentative reactions with anaerobic glycolysis leading to lactate and alanine accumulation; concomitantly, levels of fermentable-free amino acids (aspartate and glutamate) decreased. Changes in free amino acid patterns in skeletal muscle and heart also indicated a reliance on amino acid fermentation during freezing, but additional increases in the levels of several other amino acids suggested that freezing might also elevate proteolysis. The results show a role for amino acids in anuran freezing survival and demonstrate that the biochemical mechanisms involved in controlling liver glucose output during freezing, previously described only for the wood frog Rana sylvatica, are probably general mechanisms for regulating cryoprotectant pools in all freeze-tolerant anurans.

Page Thumbnails

  • Thumbnail: Page 
[517]
    [517]
  • Thumbnail: Page 
518
    518
  • Thumbnail: Page 
519
    519
  • Thumbnail: Page 
520
    520
  • Thumbnail: Page 
521
    521
  • Thumbnail: Page 
522
    522
  • Thumbnail: Page 
523
    523
  • Thumbnail: Page 
524
    524
  • Thumbnail: Page 
525
    525