Maintenance of sodium and potassium ions in rat skeletal muscle fibers by serum.

1. Rat soleus (SOL) and extensor digitorum longus (EDL) muscles, stored for 2-6hrs at 30•Ž in Krebs' solution with rat serum in higher concentration than 2%, showed low internal Na and high internal K concentrations as compared with control muscles stored in the normal saline solution. Such a serum effect on the EDL muscles decreased with lowering of temperature of the external solution. 2. The rabbit, cow and cat serum in concentration of 5% as well as rat serum had a beneficial effect on the maintenance of electrolyte concentrations in EDL muscles. 3. In addition, the resting potential of EDL muscles stored in Krebs' solution with 5% rat serum at 30•Ž for 4 hrs was slightly greater than that in control muscles. A significant increase was found in the magnitude of action potential of the serum-treated muscles.