Effect of short-term spaceflight on the contractile properties of rat skeletal muscles with different functions.

In the biosatellites "Cosmos-1514" and "Cosmos-1667" rats were exposed to weightlessness in the space for either 5 or 7 days. The contractile properties of the soleus, extensor digitorum longus (EDL), brachialis, plantar, gastrocnemius and triceps (caput mediale) muscles were studied after return to earth. The muscles of animals living freely (vivarium group) and animals kept under conditions identical to those on the biosatellite (synchronous group) served as controls. The myofibrils were preserved by glycerol treatment. The ATP-Ca+(+)-induced isometric tension as well as the speed of contraction were registered, through a signal transformer, on a potentiometric recorder. The experimental results are concomitantly recorded numerically and graphically on a Citizen 1200 printer and analyzed with a Commodore 128D computer. During the short-term spaceflight the greatest weight loss and decrease of contractile power was seen in the slow soleus muscle, i.e. weightlessness and immobilization led to the degeneration and weakening of mainly the tonic muscle fibres. Nevertheless after the short-term spaceflight, even with the present improved and sophisticated methods, the authors were unable to demonstrate, changes indicating muscle transformation which had been previously seen in rats exposed to weightlessness for 18.5 days.