| Summary: | The objective of this study was to examine the metabolic plasticity of skeletal and cardiac muscle when exposed to varying temperatures. When faced with extreme temperature variation, activities of metabolic enzymes in homeothermic terrestrial mammals are directly correlated with temperature. We investigated the physiological adaptations in two extreme mammalian conditions; a diving mammal, a homeotherm, able to maintain function at low temperature and a hibernator, a heterotherm that decreases activity in response to a decrease in temperature. We measured the enzyme activity of citrate synthase, lactate dehydrogenase and catalase at 10, 25, 37 and 40°C in cardiac and skeletal muscle of the golden mantle ground squirrel (hibernator), harbor seal (diving mammal) and rat (terrestrial mammal). Surprisingly, our results indicate there is no direct correlation between temperature and enzymatic activity in the homeothermic diving mammal. In addition, the enzyme activity of the diving mammal showed a similar pattern of activity in response to temperature variation as the ground squirrel. And as expected, due to its smaller size, the ground squirrel had greater overall enzyme activity. Our results suggest there are similar adaptations in the cardiac and skeletal muscles of diving and hibernating mammals under varying temperatures that preserve enzyme function even at low environmental temperatures.
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