Direct Demonstration of Insulin Receptor Internalization: A Quantitative Electron Microscopic Study of Covalently Bound 125I-photoreactive Insulin Incubated with Isolated Hepatocytes

  1. Lelio Orci
  1. Institute of Histology and Embryology, University of Geneva Medical School Geneva, Switzerland
  2. The Banting and Best Department of Medical Research, University of Toronto Toronto, Canada
  3. Diabetes Branch, National Institute of Arthritis, Diabetes, and Digestive and Kidney Diseases, National Institutes of Health Bethesda, Maryland
  1. Address reprint requests to Dr. Phillip Gorden, Diabetes Branch, Building 10, Room 9N222, NIADDK-NIH, Bethesda, Maryland 20205.


When 125I-insulin is incubated with isolated rodent hepatocytes at 37°C, the ligand initially binds to the plasma membrane of the cell and is subsequently internalized by adsorptive endocytosis. To confirm directly that the insulin receptor is internalized with the ligand, we covalently linked photoreactive 125I-NΣB29 (azidobenzoyl) insulin to its specific hepatocyte receptor and followed its fate by quantitative electron microscopic autoradiography. We found that the covalently linked photoreactive insulin is internalized by the cell in fashion analogous to the internalization of ordinary 125I-insulin, indicating that, at least under these conditions, the insulin receptor is internalized with the ligand.

  • Received May 3, 1982.
| Table of Contents