Regulation of Glycolysis in Muscle

Abstract

SUMMARY The interconversion of glycogen phosphorylase b ti phos- phorylase a in frog sartorii contracting isotonically at 20” has been studied. When repetitive stimuli were applied, there was a lag period followed by the appearance of phosphorylase a, which increased in amount until a steady state was reached. Increasing the rate of stimulation shortened lag period and resulted in higher steady state levels of phosphorylase a. Pretreatment of muscles with epinephrine, amounts that increased the resting level of phosphorylase a only slightly, abolished the lag period completely. Changes in external work affected neither the lag period nor the steady state levels of phosphorylase a. Lowering the transmembrane potential by increasing the concentration of K+ in the external media was associated with increases in phosphorylase a even after relaxation of the initial contracture. Caffeine (lop2 M),