Regulation of Glucose Transporter and Hormone Receptor Cycling by Insulin in the Rat Adipose Cell

This chapter discusses the regulation of glucose transporter and hormone receptor cycling by insulin in the rat adipose cell. The direct measurement of glucose uptake into rat adipose cells is clearly complicated by the cell's ability to rapidly metabolize this transport substrate. This problem has been overcome by using nonmetabolizable glucose analogs—such as L-arabinose, L-xylose, 2-deoxyglucose, and 3-O-methylglucose—of which the latter is now considered the analog of choice. In almost the entire cell types so far investigated, insulin has been shown to be internalized and degraded through receptor-mediated endocytosis. Unlike many cell types, chronic exposure of the rat adipose cell to insulin results in very little apparent loss of cell surface insulin receptors-so-called “down-regulation.” The rapidity with which the insulin receptor is internalized in the rat adipose cell parallels the stimulation of both glucose transport and the redistribution of IGF-II receptors by insulin. The rapidity with which the insulin receptor is internalized in the rat adipose cell parallels the stimulation of both glucose transport and the redistribution of IGF-II receptors by insulin.