Rotation of actin monomers during isometric contraction of skeletal muscle

Julian Borejdo, Priya Muthu, John Talent, Irina Akopova, Thomas P. Burghardt

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


Cyclic interactions of myosin and actin are responsible for contraction of muscle. It is not self-evident, however, that the mechanical cycle occurs during steady-state isometric contraction where no work is produced. Studying cross-bridge dynamics during isometric steady-state contraction requires an equilibrium time-resolved method (not involving application of a transient). This work introduces such a method, which analyzes fluctuations of anisotropy of a few actin molecules in muscle. Fluorescence anisotropy, indicating orientation of an actin protomer, is collected from a volume of a few attoliters (10-18 L) by confocal total internal reflection (CTIR) microscopy. In this method, the detection volume is made shallow by TIR illumination, and narrow by confocal aperture inserted in the conjugate image plane. The signal is contributed by approximately 12 labeled actin molecules. Shortening of a myofibril during contraction is prevented by light cross-linking with 1-ethyl-3-[3-dimethylamino)-propyl]-carbodiimide. The root mean-squared anisotropy fluctuations are greater in isometrically contracting than in rigor myofibrils. The results support the view that during isometric contraction, cross-bridges undergo a mechanical cycle.

Original languageEnglish (US)
Article number014013
JournalJournal of Biomedical Optics
Issue number1
StatePublished - Jan 2007


  • Actin
  • Isometric contraction
  • Microscopy
  • Muscle
  • Total internal reflection

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Atomic and Molecular Physics, and Optics
  • Biomedical Engineering
  • Biomaterials


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