Insulin, insulin-like growth factor-I (IGF-I) and glucagon: the evolution of their receptors.

Insulin and glucagon, two of the most studied pancreatic hormones bind to specific membrane receptors to exert their biological actions. Insulin-like growth factors IGF-I and IGF-II are structurally related to insulin, although they are expressed ubiquitously. The biological functions of the IGFs are mediated by different transmembrane receptors, which includes the insulin, IGF-I and IGF-II receptors.

Insulin-family peptide-receptor interaction at the early stage of vertebrate evolution.

This is an overview of our studies on insulin and insulin-like growth factor-I (IGF-I) interactions with their own and each other's receptors in the lamprey (Lampetra fluviatilis L.), an extant representative of the ancient vertebrate group of Agnathans as compared to mammal (rat). Lamprey insulin receptor shows species specificity, namely, it binds its own insulin with higher affinity than mammalian hormone.

Lamprey but not porcine insulin binds with different affinity to lamprey and rat hepatocytes.

The displacement of porcine [125I] insulin bound to rat and lamprey isolated hepatocytes with unlabeled lamprey and porcine insulins was investigated. Binding affinity of lamprey insulin for insulin receptor of rat was similar to that of porcine insulin. In contrast, the binding affinity of lamprey insulin for its own insulin receptor was higher than for a rat receptor.

Insulin and insulin-like growth factor-I receptors in fish brain.

We investigated insulin and insulin-like growth factor-I (IGF-I) receptor-binding and receptor intrinsic tyrosine kinase activity in the brain of carp (Cyprinus carpio) and trout (Salmo trutta fario). Glycoprotein fractions of semi-purified receptors were prepared by WGA-agarose affinity chromatography. Insulin receptors were found in the brains of both fish species investigated.

Insulin receptor downregulation in isolated hepatocytes of river lamprey (Lampetra fluviatilis).

Insulin receptor downregulation in the isolated hepatocytes of lamprey (Lampetra fluviatilis) was studied at the ambient temperature for this species. Preincubation of hepatocytes with 10(-9)-10(-8) M unlabeled insulin decreased insulin binding capacity to 43, 37, and 34% at 4, 15, and 25 degrees, respectively. Preincubation of hepatocytes in the presence of 10(-10) M unlabeled insulin had no effect on the 125I-insulin binding.

Receptor-mediated endocytosis of insulin in lower vertebrates: internalization and intracellular processing of 125I-insulin in isolated hepatocytes of lamprey and frog.

The binding of 125I-insulin to cellular insulin receptors and the internalization of insulin-receptor complexes have been studied in isolated hepatocytes of frog and lamprey. Two classes of binding sites (Kd 10(-9) and 10(-8) M) were found in cells of both species. The molecular weight of the insulin receptor alpha-subunit was 130 kDa in both species.

[Receptor-mediated endocytosis in the cells of cold-blooded animals. II. The fate of internalized 125I-insulin in the isolated hepatocytes of the lamprey and the frog].

The 125I-insulin outflow from isolated hepatocytes of the frog and lamprey "loaded" with the labeled hormone has been studied. It is shown that the ligand outflow from the frog cells increased with the increase in the incubation temperature from 0 up to 20 degrees C. The curves of the rest cell radioactivity were reciprocal to those of the radioactivity accumulated in the medium at the corresponding temperatures.

[Receptor-mediated endocytosis in the cells of cold-blooded animals. I. Insulin internalization in the hepatocytes of the lamprey and the frog].

A method of preparation of the lamprey and frog isolated hepatocytes is described. The binding of 125I-insulin to the cell receptors and the internalization of insulin--receptor complexes in hepatocytes have been studied at the temperature of species survival. Two classes of binding sites (with Kd equal to 10(-9) and 10(-8) M, resp.

[Certain biochemical characteristics of an insulin-like substance from the bivalve mollusk Anodonta cygnea].

An insulin-like substance (ILS) was isolated from the visceral organs of the bivalve mollusc Anodonta cygnea by chromatography on a sulfocationite CU-23 and purified by reverse phase liquid chromatography. ILS was shown to be made up to several fractions with Mr ranging from 9 to 20 kDa which have identical amino acid composition but different hydrophobicity and N-terminal amino acids. It was supposed that the heterogeneity of ILS fractions is due to its genetical or posttranslational polymorphism.

[Glucagon receptor binding and its effect on the cAMP level in isolated rat and chicken hepatocytes].

The binding sites to glucagon with KD 10(-9) M in rat and chicken isolated hepatocytes and with KD 10(-7) M in chicken hepatocytes only where revealed. The first, but not the second binding sites where decreased in their affinity by the adding of GTP nonhydrolyzing analogue Gpp(NH). Glucagon activated the cAMP accumulation in rat and chicken hepatocytes in dose-depended manner.

[Glucagon binding by isolated chick hepatocytes].

Studies have been made on the binding of 125I-glucagon by isolated chick hepatocytes. It was shown that pH and temperature dependence of the binding does not differ from that in rat hepatocytes. Optimum binding was observed at pH 7.

[Insulin binding by receptors of the plasma membranes of the liver in hens in ontogenesis].

Specific binding of 125I-insulin to the liver plasma membranes was studied in the chick embryos from the 10th day of incubation on, in chickens and adult fowl. The level of binding was the same in all cases although the insulin concentration of blood increases during ontogenesis, the number of receptors and their affinity to the hormone remaining constant. The data on insulin-receptor interactions in the liver have been compared with the earlier results of the authors obtained on the chick skeletal muscle and erythrocytes.

[Insulin receptor reaction of the lamprey Lampetra fluvialis to hyperinsulinemia induced by administration of the hormone].

Insulin injections to the lamprey Lampetra fluviatilis result in prolonged and significant hyperinsulinemia, but do not decrease the number of receptors in its target cells. These findings were made in studies on the specific binding to 125I-insulin by membrane fractions of the brain and cardiac muscle in migrating and winter (fasting) lampreys. It is also suggested that no regulation of the number of the receptors by hormonal level takes place in the lamprey, which is presumably due to a low rate of internalization of hormone-receptor complexes and to a total decrease in the turnover of the receptors in a pre-spawning period.

[Erythrocyte insulin receptors in the ontogeny of chickens].

Specific binding of 125I-insulin by the erythrocytes was studied in the chick embryos, chicken and adult fowl. The binding was shown to decrease during ontogenesis. The maximal level of binding was observed in the chick embryos.

[Brain insulin receptors in the evolution of vertebrates].

Studies have been made on 125I-insulin binding for brain membranes from cyclostomes (the lamprey Lampetra fluviatilis), fish (pink salmon Oncorhynchus gorbuscha) and mammals (rats). The species studied differed by the level of binding (the highest in the rat and the lowest in the lamprey), which was due mainly to differences in the number of binding sites per membrane protein. Qualitative properties of the receptors in the species studied were found to be very similar.

[Study of insulin-receptor interactions in plasma membrane of rat liver using antibodies against insulin].

Preincubation of rat liver cell plasma membranes with antiinsulin serum (AIS) results in a 3-fold increase of specific binding of [125I]insulin added to AIS-free membranes. The degree of such increase depends on preincubation time and AIS concentration; at a rise of both parameters the dependence curve shown a plateau. The Scatchard plots suggest that preincubation with AIS increases the high and low affinity of binding sites; their number remains thereby unchanged.

[Comparative study of binding of Scorpaena porcus scorpion fish insulin and pig insulin by specific muscle plasma membrane receptors].

Insulin from the scorpion-fish and porcine insulin have been compared with respect to their capacity to interact with the specific receptors in plasma membrane of skeletal muscle fibers of rats. Both insulins inhibited membrane binding of insulin-125J; the dose of porcine insulin which inhibited binding by 50% was equal to 3.7 nM, that of fish insulin -- to 100 nM.

[Interaction of insulin and its receptors in the muscles: specific I125 binding with plasma membranes of the skeletal muscle of rat].

A preparation of plasmatic membranes of the rat skeletal muscle was obtained which was used to characterize the interaction of insulin with its receptors in the myocyte. It was shown that insulin-125I binding by the membranes depended on the incubation time and temperature; the maximum binding occurred at 4 degrees, although the binding rate was low at this temperature. The degrading of labeled insulin at 4 degrees C did not exceed 1% in the course of 24 hours of incubation with the membranes.