Up-regulation of insulin binding in fish skeletal muscle by high insulin levels.
The effects of insulin titres on regulation of receptor binding were studied in several fish species. Insulin receptors were semi-purified by affinity chromatography (WGA-agarose) from skeletal muscle of carp, brown trout and rainbow trout that had been subjected to increases in insulinemia produced either by arginine injection, food administration, or adaptation to an experimental diet (extruded diet with high-digestibility carbohydrates). Arginine injection provoked acute hyperinsulinemia in both carp and trout. Specific binding of insulin to the skeletal muscle was significantly increased 3 h after injection (from 5.8 +/- 0.3 to 9.6 +/- 0.9%/10 micrograms protein in carp and from 0.8 +/- 0.2 to 1.5 +/- 0.4%/10 micrograms in trout). The same effect was observed in carp liver preparations (from 6.0 +/- 0.75 to 9.9 +/- 1.25%/10 micrograms). No alterations in tyrosine kinase activity of the receptors were detected in either carp or trout preparations: basal activities of the receptors were maintained (3100 +/- 200 fmol P/fmol receptors/30 min and 3700 +/- 400 fmol P/fmol receptors/30 min, in carp and trout, respectively), as were the percentage of stimulation over basal levels obtained by incubation with insulin (227 +/- 25% and 160 +/- 10% respectively). Food ingestion raised plasma insulin levels more steadily. Specific binding also increased in skeletal muscle preparations, especially in carp (from 5.7 +/- 0.3 to 11 +/- 1.7%/10 micrograms at 4 h and 10 +/- 0.7%/10 micrograms at 8 h). Tyrosine kinase activity was maintained without significant changes. Rainbow trout adapted for 2 months to an extruded diet presented higher insulin titres and higher glycogen reserves in liver and muscle. Insulin binding to skeletal muscle preparations was also significantly increased (from 0.36 +/- 0.02 to 0.77 +/- 0.1%/10 micrograms), as was tyrosine kinase activity (from 132 +/- 4% to 156 +/- 6%, without alterations in the basal activity). Results showed that fish can respond to both acute and maintained increases in insulinemia by increasing the number of insulin receptors. Tyrosine kinase activity, in contrast, is only modified after long-term adaptation.
Departament de Bioquímica i Fisiologia, Facultat de Biologia, Universitat de Barcelona, Spain.
M
M
Párrizas
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N
Baños
J
J
Baró
J
J
Planas
J
J
Gutiérrez
D000704:Analysis of Variance; D000818:Animals; D001120:Arginine / Q000494:pharmacology; D002347:Carps; D002846:Chromatography, Affinity; D004040:Dietary Carbohydrates / Q000494:pharmacology; D004958:Estradiol / Q000494:pharmacology; D007328:Insulin / Q000494:pharmacology*; D007700:Kinetics; D008099:Liver / Q000378:metabolism; D018482:Muscle, Skeletal / Q000378:metabolism*; D017686:Oncorhynchus mykiss; D011972:Receptor, Insulin / Q000187:drug effects / Q000302:isolation & purification / Q000378:metabolism*; D012016:Reference Values; D013045:Species Specificity; D013997:Time Factors; D014337:Trout; D015854:Up-Regulation / Q000187:drug effects
D004040:Dietary Carbohydrates; D007328:Insulin; D004958:Estradiol; D001120:Arginine; D011972:Receptor, Insulin