Insulin and IGF-I binding and tyrosine kinase activity in fish heart

Abstract

Abstract A study is presented of the binding of insulin and IGF-I to their respective receptors in the heart muscle of carp (Cyprinus carpio), coho salmon (Oncorhynchus kisutch), brown trout (Salmo trutta fario) and Sprague–Dawley rats. Receptor preparations were partially purified by wheat germ agglutinin affinity chromatography. Specific binding of insulin/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 the 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 binding of IGF-1/100 mg fish heart preparation ranged between 44 and 68%, surpassing IGF-I binding in the rat heart (20 ± 6%). The affinity of IGF-I receptors in fish heart (Kd 0·17–0·19 nm) was higher than that in rat heart (Kd 0·40 ± 0·05 nm) or insulin receptors in fish and rat heart preparations (0·25–0·72 nm). The IGF-I receptor binding was highly specific and required at least 100 nm insulin to cause any displacement 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 stimulation of tyrosine kinase activity (210–230%) in fish heart was in the same range as in other piscine tissues (150–260%) or in rat cardiac muscle (200–250%). Journal of Endocrinology (1995) 146, 35–44