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Kinetic properties of cardiac myosin heavy chain isoforms in rat

Stefan Galler1, Emma Puchert, Bärbel Gohlsch

  • 1Zoologisches Institut, Universität Salzburg, Hellbrunnerstrasse 34, 5020 Salzburg, Austria. Stefan.Galler@sbg.ac.at

Pflugers Archiv : European Journal of Physiology
|November 29, 2002
PubMed

Insights

Cardiac myosin heavy chain (MHC) kinetics differ significantly. Cardiac alphaMHC is 3x faster than betaMHC, with distinct properties compared to skeletal muscle MHC isoforms.

Area of Science:

  • Muscle Physiology
  • Molecular Biology
  • Biochemistry

Background:

  • Myosin heavy chain (MHC) head is crucial for force generation in muscle.
  • Previous studies indicated MHC isoform-specific differences in myosin head kinetics.
  • Stretch activation kinetics in skeletal muscle correlate with MHC isoform composition.

Purpose of the Study:

  • To investigate and compare the kinetic properties of cardiac alpha-MHC and beta-MHC isoforms.
  • To compare the stretch activation kinetics of cardiac MHC isoforms with those in rat skeletal muscle fibers.

Main Methods:

  • Utilized stretch activation methodology on muscle strips from hyper- and hypothyroid rat atria and ventricles.
  • Measured isometric conditions and maximal Ca2+ activation to assess kinetic properties.
  • Compared kinetic parameters (time constant t3) between different muscle types and MHC isoforms.

Main Results:

  • Cardiac alpha-MHC kinetics were found to be 3 times faster than cardiac beta-MHC under isometric conditions and maximal Ca2+ activation.
  • 100% alpha-MHC heart muscle strips showed faster stretch activation kinetics (t3: 108+/-18 ms) than rat type-IIA skeletal muscle fibers (t3: 157+/-19 ms).
  • 100% beta-MHC heart muscle strips exhibited faster kinetics (t3: 351+/-44 ms) compared to rat type-I skeletal muscle fibers (t3: 901+/-348 ms).

Conclusions:

  • Cardiac alpha-MHC and beta-MHC isoforms possess distinct kinetic properties.
  • The observed kinetic differences between cardiac beta-MHC and skeletal muscle type-I fibers challenge the assumed identity between beta-MHC and MHCIbeta.

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