Premium
Observing cycling of a few cross‐bridges during isometric contraction of skeletal muscle
Author(s) -
Mettikolla P.,
Calander N.,
Luchowski R.,
Gryczynski I.,
Gryczynski Z.,
Borejdo J.
Publication year - 2010
Publication title -
cytoskeleton
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.95
H-Index - 86
eISSN - 1949-3592
pISSN - 1949-3584
DOI - 10.1002/cm.20453
Subject(s) - myosin , isometric exercise , actin , biophysics , contraction (grammar) , biology , protein filament , muscle contraction , anatomy , microbiology and biotechnology , biochemistry , endocrinology , physiology
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.