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Cardiac energetics: sense and nonsense
1Department of Physiology, Monash University, Melbourne, Victoria, Australia. colin.gibbs@med.monash.edu.au
Clinical and Experimental Pharmacology & Physiology
|August 2, 2003
Summary
Mouse hearts have unique mechanics and energetics compared to humans, with energy per beat being a third of human hearts. Force, not shortening, is the key determinant of cardiac energy usage.
Area of Science:
- Cardiology
- Physiology
- Biophysics
Background:
- Detailed mouse heart mechanics and energetics are crucial in the genomic era.
- Mouse heart excitation-contraction (EC) coupling differs from rat hearts.
- Species differences in myocardial oxygen consumption are not solely due to heart rate.
Purpose of the Study:
- To outline current ideas in cardiac energetics.
- To stress the need for detailed mouse heart mechanics and energetics knowledge.
- To analyze energy usage in mouse and human hearts.
Main Methods:
- Comparison of mouse and human heart energetics.
- In vivo and in vitro metabolic measurements.
- Cardiac modeling using Huxley and Hill/Eisenberg variants.
Main Results:
- Mouse heart energy per beat is approximately one-third of human heart.
- Significant species differences exist in non-beating heart metabolism.
- Activation heat accounts for 20-25% of active energy per beat; force is the major determinant of energy usage.
- 'Loose coupling' is necessary in models to replicate low cardiac energy flux at low afterloads.
Conclusions:
- The common assumption about heart rate explaining species differences in oxygen consumption is incorrect.
- Basal heart metabolism is regulatable and may be influenced by the endothelium.
- Force generation, rather than shortening, is the primary driver of cardiac energy consumption.