Insulin-stimulated glucose transport in human adipocytes.

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Abstract
3-O-methylglucose was used to assess basal and insulin-stimulated glucose transport in isolated human adipocytes. Time-course studies demonstrated that the sugar is rapidly taken up by isolated cells, and transmembrane equilibrium is established with 5 min at 37.degree. C. The transport rate is temperature-dependent, and the half-time (t1/2) to equilibrium is incrased from 55 .+-. 6 to 120 .+-. 14 s by decreasing the temperature from 37 to 24.degree. C. 3-O-methylglucose, D-glucose, and 2-deoxyglucose all share a common glucose transport system because D-glucose and 2-deoxyglucose inhibit 3-O-methylglucose transport in a competitive manner. Cytochalasin B inhibits all but the diffusion-mediated component of uptake and L-glucose does not compete at all with 3-O-methylglucose for transport. When the initial rate of transport is measured, a readily detectable insulin stimulation can be observed. Insulin leads to a dose-dependent 3-fold increase in the initial rate of 3-O-methylglucose transport with half-maximal effects at an insulin concentration of 0.6 .+-. 0.04 ng/ml and maximal stimulation at 25 ng/ml; this stimulation is due to an increase in Vmax, whereas the Km (6 mM) of the transport system is unchanged. Human fat cells possess a stereospecific D-glucose transport system that in many ways is ismilar to the rat adipocyte glucose transport system. With a rapid assay technique that allows measurements of the initial rate of 3-O-methylglucose uptake, the ability of insulin to increase glucose transport into human fat cells can readily be measured.

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