Cell Water, Sodium, And Potassium In Red And White Mammalian Muscles
Cell water, sodium, and potassium were determined in 12 different hind limb muscles and in the diaphragm of the rat to evaluate differences between white and red muscles. Red muscles (e.g., soleus, crureus, diaphragm) have a larger extracellular inulin space, higher [Na]i and lower [K]i than white muscles. Mixed muscles (e.g., gastrocnemius, rectus femoris) have intermediate values depending on the ratio of red and white fibers. The sum of intracellular [Na + K] is approximately the same in all muscles. There is no distinct demarcation between white and red fibers in mixed muscles. Histological observations revealed that the terms "red" and "white" as applied to the whole muscle do not imply homogeneity of the component fibers. Moreover, the distribution of the red and white fibers was not uniform in any of the hind-limb muscles examined.