Retroendocytosis of insulin in rat adipocytes

Journal Article · Fri Aug 01 04:00:00 EDT 1986 · Endocrinology; (United States)

DOI:https://doi.org/10.1210/endo-119-2-572· OSTI ID:5095837

Levy, J R; Olefsky, J M

A variety of ligands internalized by receptor-mediated endocytosis follow a short circuit pathway that does not lead to degradation but results in rapid exocytosis of intact ligand, a process termed retroendocytosis. We studied the time course of (/sup 125/I)iodoinsulin processing and retroendocytosis after internalization in isolated rat adipocytes. After steady state binding and internalization, surface receptor-bound insulin was removed by exposing cells to a low pH at low temperatures. The cells containing internalized (/sup 125/I)iodoinsulin were reincubated in fresh medium; subsequently, the radioactivity remaining within the cells and released into the medium were analyzed at various times by trichloroacetic acid (TCA) precipitation, Sephadex G-50 gel filtration, and reverse phase HPLC. Cell-associated radioactivity progressively decreased after reincubation in 37 C buffer, with 50% released in 9 min and 85% by 45 min. In the media, TCA-precipitable material appeared quickly, with a t1/2 of 2 min, and plateaued by 10 min. TCA-soluble material was released continually throughout the 45-min period. The release of both TCA-precipitable and TCA-soluble material was temperature and energy dependent. Sephadex G-50 chromatography demonstrated the loss of insulin from the intracellular pool and its appearance in the medium with a time course similar to that of TCA-precipitable material. Reverse phase HPLC demonstrated that the intracellular and medium radioactivity eluting in peak II (insulin peak) on Sephadex G-50 was composed of both intact insulin and intermediates. After the internalization of insulin, rat adipocytes release not only small mol wt degradation products of insulin, but also insulin intermediates and intact insulin. The rate of retroendocytosis reported here is almost identical to the rate of insulin receptor recycling in rat adipocytes.

• Research Organization: Veterans Administration Medical Center, San Diego, CA
• OSTI ID: 5095837
• Journal Information: Endocrinology; (United States), Journal Name: Endocrinology; (United States) Vol. 2; ISSN ENDOA
• Country of Publication: United States
• Language: English

Related Subjects

550501* -- Metabolism-- Tracer Techniques
59 BASIC BIOLOGICAL SCIENCES
ADIPOSE TISSUE
ANIMAL CELLS
ANIMAL TISSUES
ANIMALS
BETA DECAY RADIOISOTOPES
BODY
CONNECTIVE TISSUE
CONNECTIVE TISSUE CELLS
DAYS LIVING RADIOISOTOPES
ELECTRON CAPTURE RADIOISOTOPES
FAT CELLS
HORMONES
INSULIN
INTERMEDIATE MASS NUCLEI
IODINE 125
IODINE ISOTOPES
ISOTOPE APPLICATIONS
ISOTOPES
LABELLED COMPOUNDS
MAMMALS
MEMBRANE PROTEINS
METABOLISM
NUCLEI
ODD-EVEN NUCLEI
ORGANIC COMPOUNDS
PEPTIDE HORMONES
PROTEINS
RADIOISOTOPES
RATS
RECEPTORS
RODENTS
SOMATIC CELLS
TISSUES
TRACER TECHNIQUES
VERTEBRATES