Insulin and insulin-like growth factor-I receptors in fish brain

• Published in: Regulatory peptides 1996-02, Vol.61 (2), p.155-161
• Main Authors: Leibush, B., Párrizas, M., Navarro, I., Lappova, Y., Maestro, M.A., Encinas, M., Plisetskaya, E.M., Gutiérrez, J.
• Format: Article
• Language: English
• Subjects: Animals; Binding, Competitive; Brain; Brain - metabolism; Carp; Carps - metabolism; Chromatography, Affinity; IGF-I binding; Insulin; Insulin - metabolism; Insulin-Like Growth Factor I - metabolism; Membrane Glycoproteins - isolation & purification; Peptides - metabolism; Phosphotransferases - metabolism; Protein Binding; Protein-Tyrosine Kinases - metabolism; Receptor, IGF Type 1 - metabolism; Receptor, Insulin - metabolism; Trout; Trout - metabolism
• ISSN: 0167-0115; 1873-1686
• DOI: 10.1016/0167-0115(95)00154-9

We investigated insulin and insulin-like growth factor-I (IGF-I) receptor-binding and receptor intrinsic tyrosine kinase activity in the brain of carp ( Cyprinus carpio) and trout ( Salmo trutta fario). Glycoprotein fractions of semi-purified receptors were prepared by WGA-agarose affinity chromatography. Insulin receptors were found in the brains of both fish species investigated. Carp and trout brain preparations bound, respectively (per 50 μg glycoprotein), with 6.0 ± 1.5% and 8.0 ± 2.0% of 125I-labeled insulin added to the assay. Insulin binding was specific: much higher quantity of IGF-I (EC 50 165 ± 11 nM for carp and 88.0 ± 6 nM for trout receptors) than insulin (EC 50 0.26 ± 0.04 nM for carp and 0.25 ± 0.02 nM for trout) was necessary to displace bound insulin tracer. In preparations of brain receptors, IGF-I binding (52.8 ± 6.5% in carp brain and 55.0 ± 13.0% in trout brain) surpassed insulin binding several fold. IGF-I bound to the brain receptors with high affinity ( K d for carp was 0.13 ± 0.06 nM and for trout 0.22 ± 0.11 nM) and specificity. Although IGF-I binding could be displaced with insulin, EC 50 were 660 ± 51 nM for carp and 1557 ± 194 nM for trout. Both ligands stimulated phosphorylation of exogenous substrates in a dose-dependent manner. Carp brain receptors were not significantly different from trout receptors with respect to basal phosphotransferase activities (250.0 ± 50.0 fm P/mg glycoprotein in carp and 330.0 ± 120.0 fm P/mg glycoprotein in trout). In both species IGF-I caused higher maximal stimulation (308.0 ± 36.0% and 270.0 ± 39%, for carp and trout, respectively) than insulin (250.0 ± 13.0% and 209.0 ± 6.0%, for carp and trout, respectively).