Determination of Fermentable Sugar in Muscle. ∗

It was noted 1 that short tetanic stimulation of rat muscle resulted in an increase in fermentable sugar, suggesting that some of the split-products of glycogen escaped phosphorylation and remained as fermentable sugar in muscle. Since several intermediates might be formed between glycogen and the first phosphorylized product, it seemed of interest to determine the nature of the fermentable sugar formed as a result of contraction. It was shown previously that heart muscle contained a larger amount of fermentable sugar than resting skeletal muscle. This was attributed to the continuous activity of the former organ and made it desirable to determine the nature of the fermentable sugar in heart muscle as well.

In view of the low concentration of fermentable sugar in muscle, large amounts of tissue had to be used for each experiment. Cats were anesthetized with nembutal and the gastrocnemii dissected free of surrounding tissue for rapid removal. One muscle was stimulated tetanically for four 10-second periods through the sciatic nerve, while the other muscle served for the determination of the resting value. Generally the muscles of 2 cats were combined; these yielded from 40 to 60 gm. of resting muscle and a similar quantity of stimulated muscle.

In some preliminary experiments the muscles were frozen in a CO₂ snow-ether mixture prior to extraction. It was found that the contraction elicited by the freezing resulted in an increase in the fermentable sugar. Hence, this method of fixing the muscles was replaced by one in which the muscles were immersed immediately after removal in N sulfuric acid cooled to about—4°.

It seemed doubtful at first that a muscle of the size of a cat gastrocnemius could be fixed in this manner.