Phosphocreatine in Insulinized Frogs.

Abstract

Fiske and Subbarow 1 have isolated phosphocreatine from protein-free muscle filtrates and find “that the compound is destroyed during contraction at a rate which rivals that of glycogenolysis and lactic acid production.” Modern theories of muscle contraction have as their foundation the change of glycogen into lactic acid. But it has been shown that the muscles of insulinized frogs can contract in a normal manner even if no glycogen can be found in them. 2

To determine whether there is a correlation between glycogen and phosphocreatine we have analyzed individual gastrocnemii of very large frogs for initial phosphorus, phosphocreatine, total phosphorus, lactacidogen, glycogen, and lactic acid.

One gastrocnemius was removed with as little stimulation as possible, frozen in liquid air, and weighed portions (0.5 gm. or more) were taken for each of the different estimations. The other gastrocnemius was removed at the same time and stimulated at second intervals nearly to exhaustion, then frozen, portions weighed, etc.

In normal frogs we found 6-20 mgm. of phosphocreatine per gm. of tissue in resting muscles, and very little or none in exercised muscles. Changes in lactacidogen (i. e., total phosphorus minus initial phosphorus and phosphocreatine) were too irregular for any definite conclusions to be drawn from the data. The glycogen content of resting muscle was 6-8 mgm. per gm. of tissue, and the loss of glycogen in the exercised muscles, 1-2 mgm., was approximately balanced by the gain in lactic acid. Normal resting muscles are, therefor, high both in phosphocreatine and glycogen, and worked muscles lose all their phosphocreatine and much of their glycogen

In insulinized frogs which had had violent convulsions for several days we found the following conditions: The phosphocreatine content of resting muscles was always low, many times being entirely absent. Glycogen was also low in these muscles, in many cases being undetectable. Yet the muscles were able to do approximately their normal amount of work in lifting weights.