Glycogen metabolism in red and white muscle

Abstract

Initial concentrations of glycogen, which were lower in red than in white muscle fiber groups of rats, were maintained during the 1st hr. of a 2-hr, incubation. During the 2nd hr. of incubation the glycogen decrease in red muscle was one-half as great as in white. Ten times more label from glucose -C14 was incorporated into glycogen of red muscle (counts/min. per mg. tissue) during the first 60 min. of incubation. At the end of 2 hr. of incubation this incorporation difference was still apparent although less marked. Specific activities of both trichloroacetic acid (TCA)-soluble and residual glycogen of red muscle were higher than those of white. In red muscle the specific activity of the TCA-soluble glycogen was higher than that of the residual fraction. In vivo, the specific activity of glycogen from red muscle was also higher than that from white. These results may be interpreted as evidence that under the conditions of these experiments the pathway glucose to glycogen is more active in red muscle, and that glycogen metabolism is different in the two types of muscle.