Skeletal Muscle Fiber Atrophy: Altered Thin Filament Density Changes Slow Fiber Force and Shortening Velocity

Authors

Danny A. Riley, Medical College of Wisconsin
J. L. W. Bain, Medical College of WisconsinFollow
Janell Romatowski, Marquette UniversityFollow
Robert Fitts, Marquette UniversityFollow

Document Type

Article

Language

eng

Format of Original

6 p.

Publication Date

10-6-2004

Publisher

American Physiological Society

Source Publication

American Journal of Physiology - Cell Physiology

Source ISSN

0002-9513

Abstract

Single skinned fibers from soleus and adductor longus (AL) muscles of weight-bearing control rats and rats after 14-day hindlimb suspension unloading (HSU) were studied physiologically and ultrastructurally to investigate how slow fibers increase shortening velocity (V₀) without fast myosin. We hypothesized that unloading and shortening of soleus during HSU reduces densities of thin filaments, generating wider myofilament separations that increase V₀ and decrease specific tension (kN/m²). During HSU, plantarflexion shortened soleus working length 23%. AL length was unchanged. Both muscles atrophied as shown by reductions in fiber cross-sectional area. For AL, the 60% atrophy accounted fully for the 58% decrease in absolute tension (mN). In the soleus, the 67% decline in absolute tension resulted from 58% atrophy plus a 17% reduction in specific tension. Soleus fibers exhibited a 25% reduction in thin filaments, whereas there was no change in AL thin filament density. Loss of thin filaments is consistent with reduced cross bridge formation, explaining the fall in specific tension. V₀ increased 27% in soleus but was unchanged in AL. The V₀ of control and HSU fibers was inversely correlated (R = –0.83) with thin filament density and directly correlated (R = 0.78) with thick-to-thin filament spacing distance in a nonlinear fashion. These data indicate that reduction in thin filament density contributes to an increased V₀ in slow fibers. Osmotically compacting myofilaments with 5% dextran returned density, spacing, and specific tension and slowed V₀ to near-control levels and provided evidence for myofilament spacing modulating tension and V₀.

Comments

American Journal of Physiology - Cell Physiology, Volume 288 (October 2004): C360-C365. DOI.

Recommended Citation

Riley, Danny A.; Bain, J. L. W.; Romatowski, Janell; and Fitts, Robert, "Skeletal Muscle Fiber Atrophy: Altered Thin Filament Density Changes Slow Fiber Force and Shortening Velocity" (2004). Biological Sciences Faculty Research and Publications. 43.
https://epublications.marquette.edu/bio_fac/43