Differentiation of ob 17 preadipocytes to adipocytes. Effect of insulin on the levels of insulin receptors and on the transport of alpha-aminoisobutyrate.

Cells of a clonal cell line (ob 17) isolated from the epididymal fat pad of ob/ob mouse possess insulin receptors. Their number was increased 1.5-fold after growth arrest, with no significant change in the Kd values of the "high affinity" sites determined by extrapolation of the high affinity portion of the curvilinear Scatchard plots. With chronic insulin exposure for 3 to 11 days after confluence, ob 17 cells showed a decrease in insulin receptor concentrations from 8,000 to 1,600 high affinity sites/cell (Kd from 0.45 to 1.10(-9) M) while similar levels of "low affinity" sites were found (80,000 to 100,000 sites/cell; Kd from 10(-8) to 3 x 10(-8) M). The loss of the high affinity binding sites is accompanied by the disappearance of the stimulatory effect by insulin of alpha-aminoisobutyrate uptake. Therefore, in contrast to 3T3-L1 fibroblasts, the ob 17 cells present, in culture, a self-modulation of insulin receptors and a loss of insulin sensitivity after chronic exposure to insulin.