Receptors for the insulin-like growth factors on human erythrocytes

We have examined the presence and properties of specific receptors for the insulin-like growth factors (IGFs) on human erythrocytes (RBC). HPLC purified IGF-I and II peptides were used as ligands. RBCs were separated in density fractions representing cell groups of different ages. Binding to all cell fractions was found for both IGF tracers. Porcine insulin displaced this binding only partially, with a potency that was at least 10 times lower. IGF-II was equipotent with IGF-I in displacing [125I] IGF-I binding, but was somewhat more potent than IGF-I in displacing its homologous tracer. In the youngest cell fraction from 7 normal adults, the level of specific binding per 3 X 10(9) cells was 5.2 +/- 0.4% (mean +/- SE) and 6.3 +/- 0.5% of added radioactivity for IGF-I and IGF-II respectively. It declined rapidly as a function of cell age. Binding for unfractionated cell samples was 2.2 +/- 0.1% and 3.1 +/- 0.1% respectively. We conclude that: a) Specific receptors for the IGFs exist on human erythrocytes. b) Binding to these receptors is dependent on cell age. c) The binding in isolated young RBCs is of sufficient magnitude to permit their use for the clinical measurement of these receptors.