A combined mechanical and X-ray diffraction study of stretch potentiation in single frog muscle fibres

J Physiol. 2000 Aug 1;526 Pt 3(Pt 3):589-96. doi: 10.1111/j.1469-7793.2000.00589.x.


The nature of the force (T) response during and after steady lengthening has been investigated in tetanized single muscle fibres from Rana temporaria (4 C; 2.15 micrometer sarcomere length) by determining both the intensity of the third order myosin meridional X-ray reflection (IM3) and the stiffness (e) of a selected population of sarcomeres within the fibre. With respect to the value at the isometric tetanus plateau (To), IM3 was depressed to 0.67 +/- 0.04 during steady lengthening at approximately 160 nm s(-1) (T approximately 1.7) and recovered to 0.86 +/- 0.05 during the 250 ms period of after-stretch potentiation following the rapid decay of force at the end of lengthening (T approximately 1.3); under the same conditions stiffness increased to 1.25 +/- 0.02 and to 1.12 +/- 0.03, respectively. After subtraction of the contribution of myofilaments to the half-sarcomere compliance, stiffness measurements indicated that (1) during lengthening the cross-bridge number rises to 1.8 times the original isometric value and the average degree of cross-bridge strain is similar to that induced by the force-generating process in isometric conditions (2.3 nm), and (2) after-stretch potentiation is explained by a residual larger cross-bridge number. Structural data are compatible with mechanical data if the axial dispersion of attached heads is doubled during steady lengthening and recovers half-way towards the original isometric value during after-stretch potentiation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Electric Stimulation
  • In Vitro Techniques
  • Muscle Contraction / physiology
  • Muscle Fibers, Skeletal / chemistry*
  • Muscle Fibers, Skeletal / physiology*
  • Muscle Tonus / physiology
  • Muscle Tonus / radiation effects
  • Muscle, Skeletal / chemistry*
  • Muscle, Skeletal / physiology*
  • Protein Conformation
  • Rana temporaria
  • Sarcomeres / chemistry
  • X-Ray Diffraction