Sugar transport in fat cells: effects of mechanical agitation, cell-bound insulin, and temperature.

The effects of several factors that affect the sugar transport activity in rat epididymal fat cells were studied. The transport activity was assessed semiquantitatively by measuring the uptake of 3-O-methyl-d-glucose by the oil-flotation method. The transport activity was stimulated by mechanical agitation, such as centrifugation of cells. This effect was transient. When agitated cells were incubated at 37 °C with gentle shaking, their transport activity declined. The decline was often facilitated by the addition of glucose or pyruvate. Presumably some cell preparations were low in the source of metabolic energy that was required for this recovery process. When cells were exposed to a high concentration of insulin, washed, and suspended in fresh buffer, the effect of insulin (plus that of mechanical agitation) declined after a certain lag period. The length of this period was a function of the initial insulin concentration. The incubation temperature had different effects on the basal and plus-insulin activities. The basal activity at 25 °C was higher than that at 37 °C, while the plus-insulin activity was lower at 25 °C than at 37 °C.