"Decreased Thin Filament Density and Length in Human Atrophic Soleus Mu" by Danny A. Riley, James L. W. Bain et al.
 

Decreased Thin Filament Density and Length in Human Atrophic Soleus Muscle Fibers After Spaceflight

Document Type

Article

Language

eng

Format of Original

6 p.

Publication Date

2-2000

Publisher

American Physiological Society

Source Publication

Journal of Applied Physiology

Source ISSN

0021-8987

Original Item ID

DOI: 10.1152/jappl.2000.88.2.567

Abstract

Soleus muscle fibers were examined electron microscopically from pre- and postflight biopsies of four astronauts orbited for 17 days during the Life and Microgravity Sciences Spacelab Mission (June 1996). Myofilament density and spacing were normalized to a 2.4-μm sarcomere length. Thick filament density (~1,062 filaments/μm2) and spacing (~32.5 nm) were unchanged by spaceflight. Preflight thin filament density (2,976/μm2) decreased significantly (P < 0.01) to 2,215/μm2 in the overlap A band region as a result of a 17% filament loss and a 9% increase in short filaments. Normal fibers had 13% short thin filaments. The 26% decrease in thin filaments is consistent with preliminary findings of a 14% increase in the myosin-to-actin ratio. Lower thin filament density was calculated to increase thick-to-thin filament spacing in vivo from 17 to 23 nm. Decreased density is postulated to promote earlier cross-bridge detachment and faster contraction velocity. Atrophic fibers may be more susceptible to sarcomere reloading damage, because force per thin filament is estimated to increase by 23%.

Comments

Journal of Applied Physiology, Volume 88, No. 2 (February 2000): 567-572. DOI.

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