Relationship of binding to internatlization of 125I-insulin in isolated rat hepatocytes.

By quantitative electron microscopic autoradiographic technique, we have previously shown that 125I-insulin initially localizes to the plasma membrane of isolated rat hepatocytes and is subsequently internalized in a limited region of the peripheral cytoplasm. In the present study, we have shown that when cells are incubated at 20 degrees C, steady state binding is reached by 60 minutes and maintained up until 120 minutes of incubation while at 37 degrees C steady state binding is reached by 10 minutes and maintained for 30 minutes. Under both of these conditions, internalization of the labelled material occurs as a constant function of the binding. These data suggest that under normal conditions the binding of the ligand is an important rate limiting determinant of the internalization process.