Disproportionate Loss of Thin Filaments in Human Soleus Muscle After 17-day Bed Rest

Document Type

Article

Language

eng

Format of Original

10 p.

Publication Date

10-1998

Publisher

Wiley

Source Publication

Muscle & Nerve

Source ISSN

0148-639X

Abstract

Previously we reported that, after 17-day bed rest unloading of 8 humans, soleus slow fibers atrophied and exhibited increased velocity of shortening without fast myosin expression. The present ultrastructural study examined fibers from the same muscle biopsies to determine whether decreased myofilament packing density accounted for the observed speeding. Quantitation was by computer-assisted morphometry of electron micrographs. Filament densities were normalized for sarcomere length, because density depends directly on length. Thick filament density was unchanged by bed rest. Thin filaments/μm2 decreased 16–23%. Glycogen filled the I band sites vacated by filaments. The percentage decrease in thin filaments (Y) correlated significantly (P < 0.05) with the percentage increase in velocity (X), (Y = 0.1X + 20%, R2 = 0.62). An interpretation is that fewer filaments increases thick to thin filament spacing and causes earlier cross-bridge detachment and faster cycling. Increased velocity helps maintain power (force × velocity) as atrophy lowers force. Atrophic muscles may be prone to sarcomere reloading damage because force/μm2 was near normal, and force per thin filament increased an estimated 30%.

Comments

Muscle & Nerve, Vol. 21, No. 10 (October 1998): 1280-1289. DOI.

Link to Full Text

Share

COinS