Load-Dependent Mechanical Efficiency of Individual Myosin Heads in Skeletal Muscle Fibers Activated by Laser Flash Photolysis of Caged Calcium in the Presence of a Limited amount of ATP

  • Haruo Sugi
  • Hiroyuki Iwamoto
  • Tsuyoshi Akimoto
  • Hiroko Ushitani
Part of the Advances in Experimental Medicine and Biology book series (AEMB, volume 453)


Although a contracting muscle regulates its energy output depending on the load imposed on it (“Fenn effect”), the mechanism underlying the load-dependent energy output remains obscure. To explore the possibility that the mechanical efficiency, with which chemical energy derived from ATP hydrolysis is converted into mechanical work, of individual myosin heads changes in a load-dependent manner, we examined the auxotonic shortening of glycerinated rabbit psoas muscle fibers, containing ATP molecules almost equal in number to the myosin heads, following laser flash photolysis of caged calcium. Immediately before laser flash activation, almost all of the myosin heads in the fiber are in the state, MADPPi, and can undergo only one ATP hydrolysis cycle after activation. When the fibers were activated to shorten under various auxotonic loads, the length, force and power output changes were found to be scaled according to the auxotonic load. Both the power and energy outputs were maximal under a moderate auxotonic load. The amount of MADPPi utilized at a time after activation was estimated from the amount of isometric force developed after interruption of fiber shortening. This amount was minimal in the isometric condition, and increased nearly in proportion to the distance of fiber shortening. These results are taken as evidence that the efficiency of chemo-mechanical energy conversion in individual myosin heads changes in a load-dependent manner.


Fiber Length Thin Filament Isometric Force Sarcomere Length Myosin Head 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.


Unable to display preview. Download preview PDF.

Unable to display preview. Download preview PDF.


  1. 1.
    Fenn, W.O. J. Physiol 58, 175–203 (1923).PubMedGoogle Scholar
  2. 2.
    Woledge, R.C., Curtin, N.A. & Homsher, E. Energetic Aspects of Muscle Contraction, (Academic Press, New York) (1985).Google Scholar
  3. 3.
    Huxley, A.F. Prog. Biophys. Biophys. Chem. 7, 255–318 (1957).PubMedGoogle Scholar
  4. 4.
    Podolsky, R.J. & Nolan, A.C Cold Spring Harb. Smp. Quant. Biol 37, 661–668 (1973).CrossRefGoogle Scholar
  5. 5.
    Oiwa, K., Chaen, S. & Sugi, H. J. Physiol 437, 751–763 (1991).PubMedGoogle Scholar
  6. 6.
    Bagshaw, C.R. Muscle Contraction, (Chapman & Hall, London) (1994).Google Scholar
  7. 7.
    Sugi, H., Iwamoto, H., Akimoto, T., Ushitani, H. Proc. Natl. Acad. Sci. USA 95, ?????-????? (1998).Google Scholar
  8. 8.
    Kaplan, J.H. & Ellis-Davies, G.C.R. Proc. Natl Acad. Sci, USA 85, 6571–6575 (1988).PubMedCrossRefGoogle Scholar
  9. 9.
    McCray, J.A., Fidler-Lim, N., Ellis-Davies, G.C.R. & Kaplan, J.H. Biochemistry 31, 8856–8861 (1992).PubMedCrossRefGoogle Scholar
  10. 10.
    Goldstein, D.A. Biophys. J. 26, 235–242 (1979).PubMedCrossRefGoogle Scholar
  11. 11.
    Blinks, J.R. J. Physiol 177, 42–57 (1965).PubMedGoogle Scholar
  12. 12.
    Page, S.G. & Huxley, H.E. J. Cell Biol 19, 369–390 (1963).PubMedCrossRefGoogle Scholar
  13. 13.
    Bremel, R.D. & Weber, A. Nature New Biol 238, 97–101 (1972).PubMedGoogle Scholar
  14. 14.
    Sugi, H., Kobayashi, T., Gross, T., Noguchi, K., Karr, T. & Harrington, W.F. Proc. Natl. Acad. Sci, USA 89, 6134–6137 (1992).PubMedCrossRefGoogle Scholar
  15. 15.
    Sugi, H., Oiwa, K. & Chaen, S. in Mechanism of Myofilament Sliding in Muscle Contraction, ed. Sugi, H. & Pollack, G.H. (Plenum, New York), pp. 303–311 (1993).CrossRefGoogle Scholar
  16. 16.
    Sugi, H. Jpn. J. Physiol 43, 435–454 (1993).PubMedCrossRefGoogle Scholar

Copyright information

© Plenum Press, New York 1998

Authors and Affiliations

  • Haruo Sugi
    • 1
  • Hiroyuki Iwamoto
    • 1
  • Tsuyoshi Akimoto
    • 1
  • Hiroko Ushitani
    • 1
  1. 1.Department of Physiology School of MedicineTeikyo UniversityItabashi-ku, TokyoJapan

Personalised recommendations