Internalization model using rat liver plasma membrane for receptor-mediated endocytosis of epidermal growth factor.

We have demonstrated the internalization of epidermal growth factor (EGF) using membrane isolated from rat liver. The isolated membrane exhibited a saturation curve of the binding of 125I-EGF. Furthermore, competition between the binding of 125I-EGF and unlabeled EGF to the isolated membrane was observed. These results were similar to those obtained from whole hepatocytes. In order to confirm whether or not the present experimental system using the isolated membrane can be used for the study of receptor-mediated endocytosis, the internalization of pre-bound EGF in the isolated membrane was assessed by two different methods. First, acid-insensitive 125I-EGF time-dependently increased following incubation at 37 degrees C. Secondly, EGF became inaccessible to the exogenous 125I-anti-EGF antibody when under the same condition. These processes were dependent on adenosine triphosphate, but independent of Ca2+ and stimulated by guanosine triphosphate. These results demonstrate that receptor-mediated endocytosis occurred in the isolated membrane.