Faculty Collaboration Database

Skeletal muscle fiber atrophy: altered thin filament density changes slow fiber force and shortening velocity. Am J Physiol Cell Physiol 2005 Feb;288(2):C360-5

Date

10/08/2004

Pubmed ID

15469952

DOI

10.1152/ajpcell.00386.2004

Scopus ID

2-s2.0-12144262858 (requires institutional sign-in at Scopus site)   42 Citations

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.

Author List

Riley DA, Bain JL, Romatowski JG, Fitts RH

Author

Robert Fitts PhD Professor in the Biological Sciences department at Marquette University

MESH terms used to index this publication - Major topics in bold

Actin Cytoskeleton
Animals
Hindlimb Suspension
Male
Microscopy, Electron, Transmission
Muscle Fibers, Skeletal
Muscle, Skeletal
Muscular Atrophy
Rats
Rats, Sprague-Dawley