title: Insulin and insulin-like growth factor-I (IGF-I) binding in fish red muscle: regulation by high insulin levels.
abstract: Insulin and IGF-I binding to semi-purified red muscle receptors was characterized in brown trout, Salmo trutta and the common carp. Cyprinus carpio. The yield of glycoprotein obtained after semipurification of receptors with WGA-agarose affinity chromatography in microgram g-1 initial tissue was 210.6 +/- 21 micrograms g-1 in trout and 108.5 +/- 2.5 micrograms g-1 in carp. IGF-I specific binding (4.72 +/- 0.64%/10 micrograms glycoprotein) was 4-5-times higher than insulin binding (1.04 +/- 0.12%/10 micrograms glycoprotein) in trout red muscle. This difference in binding was due to a higher number and a greater affinity of the IGF-I (Kd, 0.21 +/- 0.03 nM) compared with the insulin (Kd, 0.67 +/- 0.06 nM) receptors in this tissue. Carp red muscle IGF-I binding (9.14 +/- 0.55%/10 micrograms glycoprotein) surpassed insulin binding (2.59 +/- 0.094%/10 micrograms glycoprotein) mainly because of a greater affinity of the IGF-I (Kd, 0.092 +/- 0.027 nM) compared with the insulin (Kd, 0.1515 +/- 0.0285 nM) receptor. IGF-I and insulin binding in carp red muscle were higher than in trout, as a consequence of a higher affinity of carp red muscle receptors. Arginine injection provoked acute hyperinsulinemia in both trout (23.3 +/- 1.01 ng ml-1) and carp (24.3 +/- 1.34 ng ml-1. Specific binding of insulin and IGF-I to the red muscle decreased 4 h after injection. In trout, a decrease of insulin and IGF-I binding of 47.0% and 63.3%, respectively was observed compared with controls, in carp, these values were 44.0% and 45.0%. The number of insulin and IGF-I receptors decreased (42-55%) but affinities did not change suggesting that receptor down-regulation is a consequence of high insulin levels.
authors.affiliation: Departament de Fisiologia, Facultat de Biologia, Universitat de Barcelona, Spain.
authors.forename: N
authors.initials: N
authors.lastname: Baños
authors.forename: T W
authors.initials: TW
authors.lastname: Moon
authors.forename: C
authors.initials: C
authors.lastname: Castejón
authors.forename: J
authors.initials: J
authors.lastname: Gutiérrez
authors.forename: I
authors.initials: I
authors.lastname: Navarro
mesh_terms: D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002347:Carps; D006023:Glycoproteins / Q000737:chemistry; D006706:Homeostasis; D007328:Insulin / Q000097:blood / Q000378:metabolism* / Q000502:physiology; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D007700:Kinetics; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D011485:Protein Binding; D017526:Receptor, IGF Type 1 / Q000378:metabolism*; D011972:Receptor, Insulin / Q000378:metabolism*; D014337:Trout
chemical_list: D006023:Glycoproteins; D007328:Insulin; D007334:Insulin-Like Growth Factor I; D001120:Arginine; D017526:Receptor, IGF Type 1; D011972:Receptor, Insulin