Chicken insulin discriminates between receptors for insulin and insulin-like growth factor I on centrally- and peripherally-derived glial cells.

Insulin and IGF-I receptors in G26-20 cells, derived from a mouse oligodendroglioma, and in RN-2 cells, derived from a rat Schwannoma, were characterized by specific binding to [125I]insulin and [125I]IGF-I respectively. In both cell lines, the Kd for insulin was 1.5 nM. Insulin receptor number was 33,000/cell for RN-2 cells and 17,000 receptors/cell for G26-20 cells. RN-2 cells have 700,000 IGF-I receptors/cell with a Kd of 2 nM while G26-20 cells have 60,000 receptors/cell with an affinity of 4.9 nM. However, the independence of these two receptor populations in each cell type was equivocal since the subunit structure of these receptors appears identical by electrophoresis. In both cell lines, competition with insulin analogs for [125I]insulin binding demonstrated chicken insulin > insulin > IGF-I. Competition for [125I]IGF-I binding showed that IGF-I was approximately 85-fold more potent than insulin. Chicken insulin was ineffective at all concentrations. Thus, chicken insulin can be used as a specific ligand to unequivocally discriminate between IGF-I and insulin receptors and effects.