[Performance of the isolated perfused soleus muscle of the rat]

The energy expenditure at resting and in contractions was measured in the rat isolated m. soleus perfused with Krebs-Khenselite solution at 37 degrees C. The muscle exerted isotonic tetanus of 0.6-sec duration with 0.1-Hz frequency. The energy expenditure at resting was 18.5 mVt/kg of dry matter, that in contractions was linearly related to amount of work. The efficiency coefficient (the work increment-energy expenditure increment ratio) was on the average 24.5%. A part of the energy released in contractions (13.9 mVt/kg of dry matter) did not depend on the amount of work.