The effect of diet on multiple site regulation of glycolysis in rat skeletal muscle. 2. Activation of PFK-1 and control of F2 6BP synthesis by PFK-2/F-2,6-BPase

Abstract

The involvement of PFK-1, F2,6BP and PFK-2/F2,6BPase in dietary fat induced alterations in insulin responsiveness of skeletal muscle was examined in rats were fed either a high fat (HF) (67%kcal) or high carbohydrate (HC) (67%kcal) diet for 21 days, ad libitum. Insulin increased the total activity of PFK-1 in EDL and soleus muscle from both HC and HF fed rats. However, the insulin-stimulated increase in PFK-1 activity in muscle obtained from HF-fed rats was significantly less than from HC-fed rats; supporting previous studies examining invitro glucose metabolism. However, data examining the role of F2,6BP in the control of glycolysis were not consistent with previous reports in liver. Insulin addition produced a significant increase in [F2,6BP] in both muscle types in HF-fed rats but not in the HC-fed rats suggesting an alteration(s) in the control of the synthesis of F2,6BP. Assay of PFK-2/F2,6BPase showed that total PFK-2 increased with the addition of insulin independent of muscle type or dietary treatment. However, only EDL active PFK-2 from the HF treatment was responsive to insulin addition. The addition of insulin resulted in an increase in both the total and active form of F2,6BPase in soleus and EDL muscles from the HC treatment group. In contrast, The active form of soleus F2,6BPase decreased significantly (50%) upon incubation with insulin in HF-fed rats, while the EDL F2,6BPase decreased 25% in HF-fed rats. These data suggest that (1) F2,6BP may not play a major role in the regulation of glycolysis in skeletal muscle and (2) increase dietary fat may alter the manner of regulation of F2,6BP synthesis/degradation.