Changes in contractile protein mRNA 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 TnCslow and TnTslow levels increasing slightly, and MLC-1slow a, MLC-1slow b, TnIslow, alpha-Tmslow, and MLC-2slow 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.