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Review
. 2002 Sep 15;543(Pt 3):731-7.
doi: 10.1113/jphysiol.2002.024729.

Hibernating without oxygen: physiological adaptations of the painted turtle

Donald C Jackson  1
Affiliations
Review

Hibernating without oxygen: physiological adaptations of the painted turtle

Donald C Jackson. J Physiol. .

Abstract

Many freshwater turtles in temperate climates may experience winter periods trapped under ice unable to breathe, in anoxic mud, or in water depleted of O(2). To survive, these animals must not only retain function while anoxic, but they must do so for extended periods of time. Two general physiological adaptive responses appear to underlie this capacity for long-term survival. The first is a coordinated depression of metabolic processes within the cells, both the glycolytic pathway that produces ATP and the cellular processes, such as ion pumping, that consume ATP. As a result, both the rate of substrate depletion and the rate of lactic acid production are slowed greatly. The second is an exploitation of the extensive buffering capacity of the turtle's shell and skeleton to neutralize the large amount of lactic acid that eventually accumulates. Two separate shell mechanisms are involved: release of carbonate buffers from the shell and uptake of lactic acid into the shell where it is buffered and sequestered. Together, the metabolic and buffering mechanisms permit animals to survive for 3-4 months at 3 degrees C with no O(2) and with circulating lactate levels of 150 mmol l(-1) or more.

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Figures

Figure 1
Figure 1. Metabolic rate depression during anoxic submergence at 24 °C (top) and 3 °C (bottom)
Note the similarity in pattern but the time scale difference and the 100-fold difference in the final metabolic values. Data adapted from Jackson (1968), Jackson & Heisler (1982) and Jackson et al. (2000).
Figure 2
Figure 2. Ion balance of turtles (Chrysemys picta picta) at 3 °C
Measured data (from Ultsch et al. 1999) were collected from normoxic animals (control) and from animals after 125 days of submergence (anoxic observed). The hypothetical result of the same increase in lactic acid with no supplemental buffering response is also shown (anoxic uncompensated), in which much of the acid is unbuffered.
See this image and copyright information in PMC

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