Cultured human Y79
retinoblastoma cells bind [125I]
iodoinsulin in a manner similar to that of other CNS and peripheral tissues. The only difference noted between the
insulin binding properties of the Y79 cells and other CNS preparations is that
insulin binding to Y79 cells is down-regulated by prolonged exposure of the cells to
insulin. By contrast, studies with the various brain preparations indicate that the brain
insulin receptor is not down-regulated by circulating levels of
insulin.
Insulin binding to Y79 cells exhibits negative cooperativity, has a pH optimum of 7.8, is responsive to
cations, and gives a curvilinear Scatchard plot. Y79 cell
insulin binding capacity is 26 fmol/100 micrograms of cell
protein, corresponding to about 125,000 binding sites per cell. These findings are the first to report
insulin binding in a human cell line of
retinal origin. The characterization of the
insulin binding in this cell line may facilitate an understanding of the relationship between
insulin and its specific functions in the human retina.