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Intracellular pH during daily torpor in Peromyscus maniculatus
1Department of Environmental, Population, and Organismic Biology, University of Colorado, Boulder 80309.
Abstract:
Intracellular and extracellular acid-base parameters during normothermy and daily torpor were examined in deer mice (Peromyscus maniculatus). [14C]Dimethyloxazolidinedione and [3H]inulin were used to assess intracellular pH in liver, heart, skeletal muscle, and brain. Buffering capacities were determined using tissue homogenates. A significant increase in plasma PCO2 and CCO2 during daily torpor indicates a respiratory acidosis. All tissues experienced a reduction in the calculated dissociation ratio of histidine imidazole groups (alpha imid) during daily torpor (16.5% for brain, approximately 10% for other tissues). Based on comparisons with physicochemical tissue buffering capacities, metabolic compensation of the respiratory acidosis occurred in liver, heart, and plasma, while brain was more acidotic than predicted. The more extensive change in brain alpha imid might influence a regulated decrease in body temperature. Comparison of acid-base parameters during daily torpor and hibernation suggests that the magnitude of acid-base modifications in mammals may be associated with the level of dormancy.
Insights
Daily torpor in deer mice causes respiratory acidosis, with metabolic compensation in most tissues. Brain tissue shows greater changes, potentially affecting temperature regulation during dormancy.
Area of Science:
- Physiology
- Comparative Physiology
- Biochemistry
Background:
- Understanding acid-base balance is crucial for physiological regulation.
- Daily torpor involves significant metabolic and physiological changes.
- Mammalian responses to altered body temperatures and metabolic states require detailed investigation.
Purpose of the Study:
- To investigate intracellular and extracellular acid-base parameters in deer mice during normothermy and daily torpor.
- To determine the extent of metabolic compensation for respiratory acidosis in various tissues.
- To explore the relationship between acid-base modifications and the level of dormancy.
Main Methods:
- Utilized [14C]Dimethyloxazolidinedione and [3H]inulin to measure intracellular pH in liver, heart, skeletal muscle, and brain.
- Determined tissue buffering capacities using homogenates.
- Analyzed plasma PCO2 and CCO2 to assess respiratory acidosis.
Main Results:
- Daily torpor induced respiratory acidosis, evidenced by increased plasma PCO2 and CCO2.
- All examined tissues showed a reduced dissociation ratio of histidine imidazole groups (alpha imid) during torpor.
- Metabolic compensation for acidosis was observed in liver, heart, and plasma, but the brain exhibited greater acidosis than predicted.
- The brain's altered alpha imid may play a role in regulated hypothermia.
Conclusions:
- Deer mice exhibit metabolic compensation for respiratory acidosis during daily torpor, with notable differences in brain tissue.
- The observed acid-base shifts, particularly in the brain, may be linked to controlled body temperature reduction.
- The extent of acid-base alterations in mammals appears correlated with the depth of dormancy, suggesting a broader physiological principle.
