Abstract

Introduction

Materials & Methods

Results

Discussion & Conclusion

References

Discussion
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Cellular homeostasis depends on the maintenance of adequate ATP levels and a near-continuous balance between ATP-generation and ATP-utilization. Since overall net metabolic rate falls dramatically during hibernation (usually to < 5% of euthermic resting rate) and since ATP-generating mechanisms are suppressed (e.g. oxygen consumption is reduced, carbohydrate catabolism is suppressed), it follows that ATP-utilizing processes must also be suppressed during hibernation. We hypothesized, therefore, that regulated suppression of cellular Na+K+-ATPase ion pump activity must occur to achieve a stable state of torpor. Maintenance of skeletal muscle energy status during hibernation in ground squirrels, Spermophilus lateralis, was accompanied by a decrease in measureable Na+K+-ATPase pump activity. Energy charge was maintained (0.89) during hibernation at the expense of the total adenylate pool (decreased by 41%). Skeletal muscle Na+K+-ATPase activity in euthermic animals was 9.1 U/mg protein but decreased during hibernation by 60% . When incubated in vitro in the presence of cyclic AMP, Na+K+-ATPase activity in extracts from euthermic animals declined to that observed in extracts of hibernator muscle but enzyme inhibition was reversed upon alkaline phosphatase treatment. Hence, enzyme suppression during hibernation appears to be due to protein phosphorylation. One effect of phosphorylation was to change the ATP dependency of the enzyme.

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Poster Number PAmacdonald0174
Keywords: hibernation, Na+K+-ATPase, energy status, ground squirrel, phosphorylation