ABUNDANT INSULIN-LIKE GROWTH-FACTOR-I (IGF-1) RECEPTOR-BINDING IN FISH SKELETAL-MUSCLE

Insulin and insulin-like growth factor-1 (IGF-I) receptors were quanti fied in glycoprotein fractions prepared by wheat germ agglutinin-agaro se affinity chromatography from skeletal muscle of several species of salmonid fish and carp. Insulin binding in fish skeletal muscle was lo wer than insulin binding found in rat. ICE-1-specific binding was two- to sixfold higher than insulin binding (16.0 +/- 3.0 versus 5.8 +/- 0 .75%/50 mu g glycoprotein in brown trout, 15.5 +/- 0.9 versus 2.2 +/- 0.5%/50 mu g in coho salmon, and 39.7 +/- 7.6 versus 16.0 +/- 3.0%/50 mu g in carp muscle). Specific IGF-I binding in fish skeletal muscle p resented values similar to those in rat muscle. IGF-1 receptor binding was, in addition, highly specific. Cold IGF-1 displaced radiolabeled IGF-1 binding in doses 100- to 1000-fold lower than cold insulin (ED(5 0) of IGF-1 binding to carp receptor preparations was 0.24 +/- 0.04 nM when displaced with cold IGF-1 and 368 +/- 83 nM when displaced with insulin). On the other hand, cold insulin displaced radiolabeled insul in binding at concentrations 10- to 100-fold lower than cold IGF-1. Re ceptor tyrosine kinase activity was stimulated over basal values in a dose-dependent manner by both insulin and IGF-1, although ICE-1 was mo re potent than insulin. Basal rates of phosphorus transferred to the a rtificial exogenous substrate poly(Glu(4):Tyr(1)) were similar in all salmonid species (200-320 fmol P/mu g protein) and higher in carp (184 0 +/- 300 fmol P/mu g protein). Maximum percentage of stimulation of t yrosine kinase activity by insulin and IGF-1 was in the same range in all salmonid species and carp (130-200% for insulin, 160-232% for IGF- 1). Abundance of IGF-1 receptors in fish skeletal muscle contrasts wit h the pattern observed in higher vertebrates, in which insulin recepto rs prevail over IGF-1 receptors. (C) 1995 Academic Press. Inc.