Monitoring Editor: Joseph Sanger
Observing cycling of a few cross-bridges during isometric contraction of skeletal muscle†
Article first published online: 25 MAY 2010
Copyright © 2010 Wiley-Liss, Inc.
Volume 67, Issue 6, pages 400–411, June 2010
How to Cite
Mettikolla, P., Calander, N., Luchowski, R., Gryczynski, I., Gryczynski, Z. and Borejdo, J. (2010), Observing cycling of a few cross-bridges during isometric contraction of skeletal muscle. Cytoskeleton, 67: 400–411. doi: 10.1002/cm.20453
- Issue published online: 25 MAY 2010
- Article first published online: 25 MAY 2010
- Manuscript Accepted: 21 APR 2010
- Manuscript Revised: 15 APR 2010
- Manuscript Received: 11 DEC 2009
During muscle contraction a myosin cross-bridge imparts periodic force impulses to actin. It is possible to visualize those impulses by observing a few molecules of actin or myosin. We have followed the time course of orientation change of a few actin molecules during isometric contraction by measuring parallel polarized intensity of its fluorescence. The orientation of actin reflects local bending of a thin filament and is different when a cross-bridge binds to, or is detached from, F-actin. The changes in orientation were characterized by periods of activity during which myosin cross-bridges interacted normally with actin, interspersed with periods of inactivity during which actin and myosin were unable to interact. The periods of activity lasted on average 1.2 ± 0.4 s and were separated on average by 2.3 ± 1.0 s. During active period, actin orientation oscillated between the two extreme values with the ON and OFF times of 0.4 ± 0.2 and 0.7 ± 0.4 s, respectively. When the contraction was induced by a low concentration of ATP both active and inactive times were longer and approximately equal. These results imply that cross-bridges interact with actin in bursts and suggest that during active period, on average 36% of cross-bridges are involved in force generation. © 2010 Wiley-Liss, Inc.