Studies on carbohydrate metabolism in rat liver slices. IX. Ionic and hormonal effects on phosphorylase and glycogen.

In 1939, Ostcrn, Herbert, and Holmes (1) reported the synthesis in vitro of glycogen in rabbit liver slices incubated in a Ringer’s solution containing 1 per cent glucose and high levels of calcium ion. This observation on rabbit liver was readily confirmed; however, no net glycogen increase could be obtained in rat liver experiments under similar conditions. Since liver slices were observed to lose intracellular potassium, it was thought that an incubation medium maintaining this cation might provide a more optimal environment for cellular synthetic functions. In 1942, Hastings and Buchanan (2) reported a net glycogen increase in liver slices from a fasted rat incubated in a medium containing potassium as the predominant cation. Further experiments in which different ionic proportions were utilized (3) demonstrated optimal glycogen synthesis in a bicarbonate medium containing K = 110, Mg = 20, and Ca = 10 mmoles per liter equilibrated at pH 7.4 to 7.5 with 5 per cent COS-95 per cent OZ. Incubating slices in a similar medium in which potassium had been replaced by sodium resulted in decreased net glycogen synthesis and a proportionate increase in the production of glucose. This “ion effect” in altering the glucose to glycogen ratio was thought to result from the inhibition or activation of one of the four known enzymes catalyzing the interconversion of glucose and glycogen; namely, phosphorylase, phosphoglucomutase, glucokinase, or glucose-6-phosphatase. Paper VIII (4) has shown essentially no difference in the activity of glucose-6-phosphatase or glucose phosphorylation between liver slices incubated in the two ionic media, The data presented in this paper demonstrate an increased level of phos-