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Insulin processing in primary endosomes is not responsible for insulin resistance observed in parametrial adipocytes from lactating rats


, : Insulin processing in primary endosomes is not responsible for insulin resistance observed in parametrial adipocytes from lactating rats. Biochimica et Biophysica Acta 1010(2): 237-245

The fate of [125I]insulin and the insulin was characterized in parametrial adipocytes from virgin rats. Parallel experiments were carried out on parametrial adipocytes from 2-4-day lactating rats, which are insulin resistant. Similar results were obtained in adipocytes from either group of animals. Insulin caused 10% of the plasma membrane insulin receptor to be translocated to a compartment resistant to extracellular trypsin. The intracellularly located insulin in receptor rapidly recycled to the plasma membrane at 37.degree. C. An endosomal compartment involved in both the endocytosis and subsequent recycling of [125I]insulin and the insulin receptor to the plasma membrane was identified on sucrose density floatation gradients. [125I]Insulin internalized at 37.degree. C accumulated in a fraction of modal density 1.12 g/ml. Crosslinking experiments revealed the presence of intact [125I]insulin-insulin receptor complexes in endosomes. After a pulse with [125I] radioactivity recovered in the endosome compartment was intact [125I]insulin. The remainder was composed of low molecular weight degradation products. Endosomal 125I radioactivity was rapidly retroendocytosed to the medium with a mean half-life of 6 min. These results suggest: (1) [125I]insulin and the insulin receptor are internalized by parametrial adipocytes into an early endosomal compartment (primary endosomes), form which the receptor, intact [12%I]insulin, and [125I]tyrosine are returned to the cell surface: and (2) the damping of the insulin signal observed in parametrial adipocytes from lactating rats is not expressed at the level of altered endocytotic processing of [125I]insulin and the insulin receptor.

US$19.90

PMID: 2643441

DOI: 10.1016/0167-4889(89)90167-5


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