SYNTHESIS OF GLYCOGEN FROM GLUCOSE AND LACTATE IN ISOLATED RAT SOLEUS MUSCLE

Glycogen synthesis was studied in isolated rat soleus muscle following a period of anaerobic preincubation to deplete the glycogen level. Synthesis was unaffected by varying either the anions or divalent cations present in the incubation medium, however, monovalent cations had a marked effect. Sodium ions promoted glycogenesis while potassium ions led to glycogen depletion. In contrast to the synthesis observed using glycogen-depleted muscle, synthesis in freshly isolated muscle appeared to be limited by the availability of glucose. It was also found that incorporation of 14C-labelled glucose into muscle glycogen always exceeded net synthesis of glycogen. From this it was concluded that net synthesis represented the difference between the amount of glycogen formed in the peripheral fibers of the tissue where glucose and oxygen were readily available, and the amount of glycogen used in the innermost fibers where the availability of glucose and oxygen was limited. Lactate stimulated the formation of glycogen in the presence of glucose, but was itself ineffective as a precursor for glycogen synthesis. The incorporation of 14C-labelled lactate into muscle glycogen is considered to represent a functional reversal of glycolysis, however, as glycogen was synthesized from glucose approximately ten times faster than labelled lactate was incorporated, direct reversal of glycolysis does not appear to be a major source of muscle glycogen. © 1969.