ag-213 and oxophenylarsine

The pharmacological characteristics, localization and process of internalization of the insulin-like growth factor I and II receptors were studied in rat primary hippocampal cultured neurons grown under serum-free conditions. [125I]insulin-like growth factor-I binding was specific with an apparent affinity (Kd) of 0.1 nM and IC50 values of 0.1, 2.9 and 99.7 nM for insulin-like growth factor-I, insulin-like growth factor-II and insulin, respectively. The competition by insulin suggests the presence of genuine insulin-like growth factor-I receptors and not insulin-like growth factor binding proteins. In contrast, [125I]insulin-like growth factor-II binding showed a Kd of 0.1 nM and IC50 values of 0.2 and 20.5 nM for insulin-like growth factor-II and insulin-like growth factor-I while insulin was inactive, a well established characteristic of the insulin-like growth factor-II receptor. Using emulsion autoradiography, specific binding sites for [125I]insulin-like growth factor-I and -II were over the whole cultured neurons. The use of selective insulin-like growth factor-I and -II receptor antibodies further confirmed the existence of these receptors in rat hippocampal cultured neurons. To investigate the respective internalization profile of [125I]insulin-like growth factor-I and [125I]insulin-like growth factor-II receptor-ligand complexes in neurons, a technique of acid stripping was used. The apparent rate of endocytosis was found to be greater for the insulin-like growth factor-II than for the insulin-like growth factor-I receptor complexes. The internalization of [125I]insulin-like growth factor-I and [125I]insulin-like growth factor-II ligand-receptor complexes was confirmed using phenylarsine oxide which significantly blocked both internalization processes. In order to eliminate possible receptor recycling, monensin was used and shown to have no effect on the internalization of either ligand. Since the insulin-like growth factor-I receptor is coupled to tyrosine kinase activity, tyrphostin 47, a specific tyrosine kinase inhibitor. was used and shown to decrease [125I]insulin-like growth factor-I but not the [125I]insulin-like growth factor-II receptor internalization profile. Accordingly, insulin-like growth factor-I is apparently internalized mostly via the insulin-like growth factor-I tyrosine kinase type receptor, while insulin-like growth factor-II is not. The insulin-like growth factor-II receptor ligand complex is likely internalized via a pathw

Topics: Animals; Arsenicals; Endocytosis; Enzyme Inhibitors; Hippocampus; Immunohistochemistry; Iodine Radioisotopes; Ionophores; Ligands; Monensin; Neurons; Nitriles; Phenols; Protein-Tyrosine Kinases; Rats; Rats, Sprague-Dawley; Receptor, IGF Type 1; Receptor, IGF Type 2; Tyrphostins