Changes in Orientation of Actin during Contraction of Muscle

Julian Borejdo, A. Shepard, D. Dumka, I. Akopova, J. Talent, A. Malka, Thomas P Burghardt

Research output: Contribution to journalArticle

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Abstract

It is well documented that muscle contraction results from cyclic rotations of actin-bound myosin cross-bridges. The role of actin is hypothesized to be limited to accelerating phosphate release from myosin and to serving as a rigid substrate for cross-bridge rotations. To test this hypothesis, we have measured actin rotations during contraction of a skeletal muscle. Actin filaments of rabbit psoas fiber were labeled with rhodamine-phalloidin. Muscle contraction was induced by a pulse of ATP photogenerated from caged precursor. ATP induced a single tumover of cross-bridges. The rotations were measured by anisotropy of fluorescence originating from a small volume defined by a narrow aperture of a confocal microscope. The anisotropy of phalloidin-actin changed rapidly at first and was followed by a slow relaxation to a steady-state value. The kinetics of orientation changes of actin and myosin were the same. Extracting myosin abolished anisotropy changes. To test whether the rotation of actin was imposed by cross-bridges or whether it reflected hydrolytic activity of actin itself, we labeled actin with fluorescent ADP. The time-course of anisotropy change of fluorescent nucleotide was similar to that of phalloidin-actin. These results suggest that orientation changes of actin are caused by dissociation and rebinding of myosin cross-bridges, and that during contraction, nucleotide does not dissociate from actin.

Original languageEnglish (US)
Pages (from-to)2308-2317
Number of pages10
JournalBiophysical Journal
Volume86
Issue number4
StatePublished - Apr 2004

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Muscle Contraction
Actins
Myosins
Anisotropy
Phalloidine
Nucleotides
Fluorescence Polarization
Actin Cytoskeleton
Adenosine Diphosphate
Skeletal Muscle
Adenosine Triphosphate
Phosphates
Rabbits

ASJC Scopus subject areas

  • Biophysics

Cite this

Borejdo, J., Shepard, A., Dumka, D., Akopova, I., Talent, J., Malka, A., & Burghardt, T. P. (2004). Changes in Orientation of Actin during Contraction of Muscle. Biophysical Journal, 86(4), 2308-2317.

Changes in Orientation of Actin during Contraction of Muscle. / Borejdo, Julian; Shepard, A.; Dumka, D.; Akopova, I.; Talent, J.; Malka, A.; Burghardt, Thomas P.

In: Biophysical Journal, Vol. 86, No. 4, 04.2004, p. 2308-2317.

Research output: Contribution to journalArticle

Borejdo, J, Shepard, A, Dumka, D, Akopova, I, Talent, J, Malka, A & Burghardt, TP 2004, 'Changes in Orientation of Actin during Contraction of Muscle', Biophysical Journal, vol. 86, no. 4, pp. 2308-2317.
Borejdo J, Shepard A, Dumka D, Akopova I, Talent J, Malka A et al. Changes in Orientation of Actin during Contraction of Muscle. Biophysical Journal. 2004 Apr;86(4):2308-2317.
Borejdo, Julian ; Shepard, A. ; Dumka, D. ; Akopova, I. ; Talent, J. ; Malka, A. ; Burghardt, Thomas P. / Changes in Orientation of Actin during Contraction of Muscle. In: Biophysical Journal. 2004 ; Vol. 86, No. 4. pp. 2308-2317.
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