CHANGES IN CONTRACTILE PROTEIN MESSENGER-RNA ACCUMULATION IN RESPONSE TO SPACEFLIGHT

Ten rats were exposed to 9 days of zero gravity aboard the National Aeronautics and Space Administration SLS-1 space mission (June 1991). Levels of fast and slow isoform mRNAs from six contractile protein gene families were quantified in the flight-soleus and extensor digitorum longus (EDL) muscles. The gene families studied were myosin light chain-1 (MLC-1), myosin light chain-2 (MLC-2), troponin (Tn) T, TnI, TnC, and tropomyosin. In the EDL muscle there was no change in slow mRNA levels with a general increase in fast mRNA levels from 23 to 232%. Changes in slow mRNA levels were seen in the flight soleus muscle with TnC(slow) and TnT(slow) levels increasing slightly, and MLC-1(slow a) , MLC-1(slow b) , TnI(slow), alpha-Tm-slow, and MLC-2(slow) levels decreasing. All fast mRNA levels increased in the flight soleus muscle from 170 to 1,100%. We can conclude that exposure to zero gravity results in 1) a general increase in fast mRNA levels in both fast and slow muscles and 2) differing directional changes in slow mRNA accumulation in the soleus muscle.