[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.) were determined in cells of both species. The molecular weight of the insulin receptor binding subunit estimated in cross-linking experiments appeared 130 kDa in the lamprey and frog, which is in agreement with the data previously obtained for the rat liver receptor. The internalization of bound 125I-insulin in both species examined occurred at the range of temperature within 0 to 20 degrees C. In the lamprey cells the maximum level of the internalized hormone remained equal at all the temperatures studied. In the frog hepatocytes, the level of internalized hormone at 5 and 20 degrees C was higher than at 0 degrees C. The data obtained show that there are no limitation of the insulin--receptor complexes endocytosis, and of the 125I-insulin internalization in hepatocytes of cold-blooded vertebrates at the survival temperature.