INSULIN AND IGF-I BINDING AND TYROSINE KINASE-ACTIVITY IN FISH HEART

A study is presented of the binding of insulin and IGF-I to their resp ective receptors in the heart muscle of carp (Cyprinus carpio), coho s almon (Oncorhynchus Kisutch), brown trout (Salmo trutta fario) and Spr ague-Dawley rats. Receptor preparations were partially purified by whe at germ agglutinin affinity chromatography. Specific binding of insuli n/100 mg cardiac muscle was much lower in fish (from 5.6 to 9.2%) than in rat (52.0 +/- 5.0%). In both carp and trout, insulin binding to th e cardiac muscle receptor preparation was significantly higher than in the white skeletal muscle (3.4 +/- 0.3%, carp and 0.9 +/- 0.3%, trout ) or in the red skeletal muscle of carp (5.5 +/- 0.8%). Specific bindi ng of IGF-I/100 mg fish heart preparation ranged between 44 and 68%, s urpassing IGF-I binding in the rat heart (20 +/- 6%) The affinity of I GF-I receptors in fish heart (K-d 0.17-0.19 nM) was higher than that i n rat heart (K-d 0.40 +/- 0.05 nM) or insulin receptors in fish and ra t heart preparations (0.25-0.72 nM). The IGF-I receptor binding was hi ghly specific and required at least 100 nM insulin to cause any displa cement of the bound ligand. Receptor tyrosine kinase activity could be stimulated in a dose-dependent manner by insulin and IGF-I, although in equimolar doses IGF-I was more potent than insulin. Maximum stimula tion of tyrosine kinase activity (210-230%) in fish heart was in the s ame range as in other piscine tissues (150-260%) or in rat cardiac mus cle (200-250%).