Changes in Orientation of Actin during Contraction of Muscle

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

Research output: Contribution to journalArticle

34 Scopus citations

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

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    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. https://doi.org/10.1016/S0006-3495(04)74288-5