Rate-limiting steps of 2-deoxyglucose uptake in rat adipocytes

2-Deoxy[1-¹⁴C]glucose uptake in rat adipocytes was measured as a function of time in the absence and presence of unlabelled glucose or 2-deoxyglucose. Uptake of tracer alone was linear from 2 s to 6 min. At 37°C the rate of uptake in insulin-stimulated cells decreased markedly after a few seconds in the presence of glucose (0.5–10 mM) and after 0.5–2 min in the presence of deoxyglucose (2–10 mM). Similar data were obtained at 22°C. With 10 mM glucose (37°C, 30 s) approx. 80% of the intracellular radioactivity was non-phosphorylated deoxyglucose and with 10 mM deoxyglucose approx. 40% was non-phosphorylated. The results show that deoxy[¹⁴C]glucose uptake after a few minutes is mainly limited by hexokinase in the presence of glucose and at least partially in the presence of deoxyglucose. The data suggest caution in using deoxyglucose uptake as a measure of transport, especially in complex kinetic studies.In addition, the initial velocity of tracer ¹$\text{3-O-}\text{methylglucose}$ was found to be approx. 2-fold higher than that of tracer deoxyglucose even though both sugars inhibited the initial velocity of labelled methylglucose half-maximally at a concentration of 5 mM. These data suggest a fundamental difference between deoxyglucose and methylglucose transport.