Insulin-like Growth Factor I Receptors and IGF-I Actions in Neuronal Cultures from the Brain

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Abstract
Neurons in primary culture have been used to study IGF-I receptors and IGF-I-induced cellular actions in the brain. Intact neurons in culture specifically bind [125I]IGF with high affinity. The potency for the competition of [125I]IGF-I binding was IGF-I > IGF-II > insulin. A curvilinear Scatchard plot represented high-affinity (0.15 nM) and low-affinity (3 nM) binding sites with a Bmax of 142 fmol and 618 fmol/mg protein, respectively. These binding sites are predominantly localized on neurites with relatively few sites on the cell soma. IGF-I induced synthesis of protein(s) in the M(r) range of 48,000-50,000 with pI values of 6.1-6.4. These observations show that IGF-I receptor mediates induction of specific proteins and suggest that these proteins may be involved in the neurotrophic activity of IGF-I in the brain.