<Outline of Experiment>
Astronauts showed muscle atrophy after space flight, even though they made efforts to do exercise during the flight. Skeletal muscle is composed of two types of muscle fibers; 1) fast muscle fibers which bear fast and large contraction within short period of time 2) slow muscle fibers which carry slow but continuous contractions for a longer period. The main structural proteins of skeletal muscle are myosin heavy chains (MHC), which have fast and slow isoforms. Under the influence of microgravity, slow muscle fibers tend to show atrophy and are turned to be fast muscle fibers, but the molecular mechanism of this phenomenon is unclear and remains to be solved.
In the Neurolab experiments, we would examine the expression of muscle specific proteins along the development of neonatal skeletal muscle under the microgravity. Especially, the influence of gravity on the transition of MHC isoforms would be analyzed in detail at protein level and mRNA level.

<Expected Outcome>
This study would provide new aspects of molecular background of muscular atrophy due to microgravity and might give new idea on preventing muscular atrophy during space flight.

Structure of muscle fibers

Flow-chart of fast muscle fibers and Slow muscle fibers

Last Updated : March 27, 1998