Bioenergetics—Conversion of Biochemical to Mechanical Energy in the Cardiac Muscle
Life is sustained by the continuous conversion of biochemical energy to mechanical energy, which is required to maintain the various functions of living organisms. This wide range of energetic activities depends on rotary and linear molecular (protein) motors of nanometer scale, which propel (bacteria, sperms), transport (messengers in neural network, cell division) generate high-energy metabolites (ATPsynthase) and perpetuate motion (muscle shortening).
This study relates to the linear molecular motor, myosin, which is energized by ATP (adenosine triphosphate) hydrolysis, and actuates muscle filament contraction. The actin-myosin filaments make up the intracellular contractile apparatus, the sarcomeres, and their relative motion, sliding one over the other, determines the functional characteristics of the contracting heart muscle.
The study explores the relationship between the biochemical energy consumption and the mechanical output of the motor units of the heart muscle. The analysis is based on coupling motor unit dynamics with free calcium binding kinetics, which regulates the motor unit activity. The calcium binds to the regulatory proteins of the contractile filaments and regulates the number of activated myosin motor units. The analysis quantifies the conversion efficiency and the determinants of the muscle’s economy. The intracellular interplay between efficiency and economy determines the adaptability of the heart muscle to the prevailing loading conditions. The analysis highlights the intracellular mechanisms and the adaptive processes that allow the heart to optimize its function under various loading conditions.
Whereas the thermodynamic efficiency of the overall metabolic transformation from biochemical energy to mechanical energy of the whole organ is 25–35%, the efficiency of energy transduction from ATP to mechanical energy ranges between 50 to 70%. This high efficiency of energy conversion reflects the extremely high efficiency of the myosin motor unit, wherein the ATPase enzyme is instrumental in ATP hydrolysis ATP + H2O ↔ ADP+P reaction and the production of mechanical energy. Finally, we discuss the notion that man is challenged by nature’s functional design in his pursuit of new horizons.
KeywordsMolecular motors crossbridge sarcomere energy conversion control cooperativity feedback mechanism contraction efficiency economy nanotechnology
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- 6.Landesberg A. End Systolic Pressure-Volume Relation Based on the Intracellular Control of Contraction. Am J Physiol. 1996; 270 (Heart Circ. Physiol. 39):H338–H349.Google Scholar
- 8.Landesberg A., Sideman S. Coupling Calcium Binding to Troponin-C and Xb Cycling Kinetics in Skinned Cardiac Cells. Am J. Physiol. 1994; 266 (Heart Circ. Physiol. 35): H1261–H1271.Google Scholar
- 9.Landesberg A., Sideman S. Mechanical Regulation in the Cardiac Muscle by Coupling Calcium Binding to Troponin-C and Xb Cycling. A Dynamic Model. Am. J. Physiol. 1994; 267 (Heart Circ Physiol 36): H779–H795.Google Scholar
- 10.Landesberg A., Sideman S. Regulation of Energy Consumption in the Cardiac Muscle: Analysis of Isometric Contractions. A Dynamic Model. Am. J. Phsyiol. 1999; 276: H998–H1011.Google Scholar
- 11.Landesberg A., Sideman S. Force Velocity Relationship and Biochemical to Mechanical Energy Conversion by the Sarcomere. Am. J. Physiol., in press, 2000.Google Scholar
- 12.Landesberg A., ter Keurs HED.T. Regulation of Force Output by the Velocity of Sarcomere Shortening in Rat Cardiac Trabecular Circulation. 1997; 96 (8): 2906.Google Scholar
- 13.Landesberg A., ter Keurs HEDJ. Crossbridge Dynamics during Shortening is Determined by Two Kinetic Components. J. Mol. Cell. Cardiol. 1998; 30: A171.Google Scholar
- 14.Landesberg A., Liu P., Lichtenstein O., Shofti R., Beyar R., Sideman S. Effect of Ejection Velocity on Pressure Generation in the Heart. In situ canine studies. VIII Mediterranean Conf. on Medical and Biological Engineering and Computing, Limassol, Cyprus, pp. 1–5, 1998.Google Scholar
- 17.Sagawa K., Maughan L., Suga H., Sunagawa K. Cardiac Contraction and the Pressure-Volume Relationship. London, UK: Oxford Univ Press, 1988.Google Scholar
- 18.Suga H. Ventricular Energetics. Physiol. Rev. 1990; 70:247–277.Google Scholar
- 20.Landesberg A., Zhang Y.M., ter Keurs HEDJ. Regulation of Tension-Length Free Calcium Relationship in the Skinned Rat Trabeculae. J. Biophysics, in press 2000.Google Scholar
- 24.Allen D.G., Kentish J.C. The Cellular Basis of the Length Tension Regulation in Cardiac Muscle. J. Mol. Cellulal Biol., 1985; 17:821–40.Google Scholar
- 26.Fozzard H.A., Haber E., Jennings R.B., Katz A.M., Morgan H.E. The Heart and Cardiovascular System. Scientific Foundations. Second Edition. NY: Raven Press, 1991: 1281–95.Google Scholar
- 27.Hill A.V. The Heat of Shortening and Dynamic Constants of Shortening. Proc. Royal Soc. London (Biol) 1938; 126: 136–195.Google Scholar
- 28.Landesberg A., Livshitz L., ter Keurs HEDJ. The Effect of Sarcomere Shortening Velocity on Force Generation, Analysis of and Verification of Models for Crossbridge Dynamics. W. Herzog, ed. John Wiley and Sons, in press 2000.Google Scholar
- 29.Mulieri L.A., Luhr G., Tvefry J., Alpert N.R. Metal-Film Thermopiles for Use with Rabbit Right Ventricular Papillary Muscle. Am. J. Physiol. 1977; 233:C146–C156.Google Scholar
- 31.Alpert N.R., Mulieri L.A., Hasenfuss G., Holubarsch C. Optimization of Myocardial Function. In Myocardial Optimization and Efficiency: Evolutionary Aspects and Philosophy of Science Considerations. D. Burkhoff, J. Schaefer, K. Schaffne, D.T. Yue, eds. Springer-Verlag: NY, 1994; 29–41.Google Scholar
- 32.Alpert N.R., Mulieri L.A., Hasenfuss G. Myocardial Chemo-Mechanical Energy Transduction. In: The Heart and Cardiovascular System, 2nd Ed; HA Fozzard et al eds. Raven Press, NY, 1992; 111–128.Google Scholar
- 35.Suga H., Goto Y., Kawaguchi O., Hata K., Takasago T., Sachi A., Taylor T.W. Ventricular Perspective of Efficiency. In Myocardial Optimization and Efficiency, Evolutionary Aspects and Philosphy of Science Consideration. D. Burkhoff, J. Schaefer, K. Schaffner, D.T. Yue (eds.) Basic Res. Cardiol., Springer-Verlag, NY. 1993; 88: 43–65.Google Scholar