Stimulatory and inhibitory effects of EDTA on sugar transport by rat soleus muscle

The uptake of D-¹⁴C]xylose by rat soleus muscle was stimulated rapidly and transiently by brief exposure to EDTA (0.1–20 mM). EDTA also stimulated xylose uptake in the presence of insulin (0.1 U/ml). Prolonged exposure to EDTA (60 min) inhibited insulin-stimulated xylose uptake and depressed ¹²⁵I-insulin binding; these effects were associated with the lowering of muscle ATP. The stimulatory effect was abolished by the substitution of Ca-EDTA (or Mg-EDTA) for EDTA; Ca-EDTA did not eliminate the inhibitory effect. There was no inhibitory effect when Ca²⁺ (5 mM) was added along with Ca-EDTA, or when Zn-EDTA was used instead. There was no effect of EGTA (5 mM) on xylose uptake measured in the presence or absence of insulin. It is concluded (1) that the stimulatory effect of EDTA is most likely due to the chelation of Mg²⁺, (2) that the inhibitory effects of EDTA are due to the chelation of some metal ion whith a higher affinity for the chelator than either Ca²⁺ or Mg²⁺.