Insulin Binding in Cultured Chinese Hamster Kidney Epithelial Cells: The Effect of Serum in the Medium

[¹²⁵I]Insulin (porcine) binding to an epithelial cell line established from a Chinese hamster kidney,$\text{CHK}-\text{AC}_{\text{E}-100}$, showed an optimum at pH 8.0 and reached a maximum after 2.5 h incubation at 25° C. Dissociation of bound [¹²⁵I]insulin was facilitated by the addition of unlabeled insulin in the dilution buffer. Porcine insulin effectively competed for [¹²⁵I]insulin binding to the cultured cells and was 30 and 90 times as potent as guinea pig insulin and porcine proinsulin in causing 50% inhibition of [¹²⁵I]insulin binding; glucagon was completely ineffective. Scatchard analysis of the binding data yielded a curvilinear plot and a capacity of 0.6 ng/10⁶ cells; the average affinity of the empty receptor,$\overline{\text{K}}_{e}$, was calculated to be 1.78 ×10⁸ M⁻¹ and that of the filled receptor,$\overline{\text{K}}_{f}$, 0.57 × 10⁸ M⁻¹. Substitution of fetal bovine serum (FBS) in the culture medium with bovine calf, bovine newborn, or bobby calf serum altered insulin binding characteristics in the cells and reduced cell growth. Insulin binding characteristics of cells grown in hormone-supplemented medium containing 0 to 0.1% FBS were similar to those of cells grown in minimum essential medium (MEM) containing 2 to 5% FBS. The data indicated that the established Chinese hamster kidney epithelial cell line$\text{CHK}-\text{AC}_{\text{E}-100}$possessed specific insulin receptors and the characteristics of the receptors could be manipulated by changing the serum in culture medium.