Maximum specific force depends on myosin heavy chain content in rat diaphragm muscle fibers

Paige C. Geiger, Mark J. Cody, Rebecca L. Macken, Gary C. Sieck

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126 Scopus citations

Abstract

In the present study, myosin heavy chain (MHC) content per half sarcomere, an estimate of the number of cross bridges available for force generation, was determined in rat diaphragm muscle (Dia(m)) fibers expressing different MHC isoforms. We hypothesize that fiber-type differences in maximum specific force [force per cross-sectional area (CSA)] reflect the number of cross bridges present per CSA. Studies were performed on single, Triton X-100-permeabilized rat Dia(m) fibers. Maximum specific force was determined by activation of single Dia(m) fibers in the presence of a high-calcium solution (pCa, -log Ca2+ concentration, of 4.0). SDS-PAGE and Western blot analyses were used to determine MHC isoform composition and MHC content per half sarcomere. Differences in maximum specific force across fast MHC isoforms were eliminated when controlled for half-sarcomere MHC content. However, the force produced by slow fibers remained below that of fast fibers when normalized for the number of cross bridges available. On the basis of these results, the lower force produced by slow fibers may be due to less force per cross bridge compared with fast fibers.

Original languageEnglish (US)
Pages (from-to)695-703
Number of pages9
JournalJournal of applied physiology
Volume89
Issue number2
StatePublished - Aug 31 2000

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Keywords

  • Fiber morphometry
  • Force per cross bridge
  • Skinned fibers

ASJC Scopus subject areas

  • Physiology
  • Physiology (medical)

Cite this

Geiger, P. C., Cody, M. J., Macken, R. L., & Sieck, G. C. (2000). Maximum specific force depends on myosin heavy chain content in rat diaphragm muscle fibers. Journal of applied physiology, 89(2), 695-703.