The Effects of Low Glycogen Content Upon the Contraction Process in Isolated Skeletal Muscle

Abstract

A large series of observations has been made to check the findings of Olmsted and Coulthard, 1 who report that gastrocnemius muscles in which little or no glycogen can be detected, taken from frogs rendered glycogen poor by means of insulin convulsions, contract upon electrical stimulation, and produce fatigue curves closely resembling the normal. They also report the increase in lactic acid content in such muscles upon fatiguing to be greater than can be accounted for by the disappearance of carbohydrate.

Analyses of the muscles of 40 normal and insulinized frogs have been made (both bull frogs and grass frogs were used). The corresponding muscles of opposite limbs were used in the determination of resting and fatigue levels. The muscles were frozen in liquid air previous to preparation for analysis. The Pflüger method, modified as suggested by Evans 2 was used in the determination of glycogen. The Friedeman, Cotonio, and Shaffer 3 method was used in the determination of lactic acid.

We have not been able to duplicate the findings of Olmsted and Coulthard. The area of the fatigue curve, at constant kymograph speed, seems to bear a direct relationship to the lactic acid produced regardless of the influence of insulin (see Fig. 1). Also, the disappearance of glycogen is closely balanced by the increase in lactic acid. In a number of cases no glycogen could be detected in the resting muscle.

In each of these cases the increase in lactic acid was sufficiently slight to have come from a resting level of glycogen below the threshold of the method used in its determination.