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Biophys. J. BioFAST: First Published March 2, 2006. doi:10.1529/biophysj.105.072413
© 2006 by the Biophysical Society.

A more recent version of this article appeared on May 15, 2006.
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MUSCLE AND CONTRACTILITY

Effect of strain on actomyosin kinetics in isometric muscle fibers

Verl B Siththanandan 1, John L Donnelly 1 and Michael Ferenczi 1*

1 Imperial College London

* To whom correspondence should be addressed. E-mail: m.ferenczi{at}imperial.ac.uk.

Submitted on August 10, 2005
Revised on September 22, 2005
Accepted on 9 February 2006


  Abstract
Investigations were conducted into the biochemical and mechanical states of cross-bridges during isometric muscle contraction. Rapid length steps (3 or 6 nm/hs-1) were applied to rabbit psoas fibers, permeabilized and isometric, at either 12 or 20°C. Fibers were activated by photolysis of NPE-caged ATP, infused into rigor fibers at saturating Ca2+. Sarcomere length, tension and phosphate release were recorded - the latter using the MDCC-PBP fluorescent probe. A reduction in strain, induced by a rapid release step, produced a short lived acceleration of phosphate release. Rates of the phosphate transient and that of phases 3 and 4 of tension recovery were unaffected by step size, but were elevated at higher temperatures. In contrast the amplitude of the phosphate transient was smaller at 20°C than 12°C. The presence of 0.5 or 1.0 mM added ADP during a release step reduced both the rate of tension recovery and the post-step isometric tension. A kinetic scheme is presented to simulate the observed data and to precisely determine the rate constants for the elementary steps of the ATPase cycle.

Key Words: ATPase enzyme kinetics, MDCC-PBP, NPE-caged ATP, model, phosphate, skeletal muscle




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Copyright © 2006 by the Biophysical Society.