Influence of Ca2+ on force redevelopment kinetics in skinned rat myocardium

William O. Hancock, Donald A. Martyn, Lee L. Huntsman, Albert M. Gordon

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Abstract

The influence of Ca2+ on isometric force kinetics was studied in skinned rat ventricular trabeculae by measuring the kinetics of force redevelopment after a transient decrease in force. Two protocols were employed to rapidly detach cycling myosin cross-bridges: a large-amplitude muscle length ramp followed by a restretch back to the original length or a 4% segment length step. During the recovery of force, the length of the central region of the muscle was controlled by using a segment marker technique and software feedback control. Tension redevelopment was fit by a rising exponential governed by the rate constant ktr for the ramp/restretch protocol and kstep for the step protocol. ktr and kstep averaged 7.06 s-1 and 15.7 s-1, respectively, at 15°C; neither ktr nor fcstep increased with the level of Ca2+ activation. Similar results were found at submaximum Ca2+ levels when sarcomere length control by laser diffraction was used. The lack of activation dependence of ktr contrasts with results from fast skeletal fibers, in which ktr varies 10-fold from low to high activation levels, and suggests that Ca2+ does not modulate the kinetics of cross-bridge attachment or detachment in mammalian cardiac muscle.

Original languageEnglish (US)
Pages (from-to)2819-2829
Number of pages11
JournalBiophysical journal
Volume70
Issue number6
DOIs
StatePublished - Jun 1996

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All Science Journal Classification (ASJC) codes

  • Biophysics

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