Separate intracellular pathways for insulin receptor recycling and insulin degradation in isolated rat adipocytes

To gain insight into the sequence of events that follow endocytotic uptake of insulin receptor complexes, we have examined the interrelationship between the degradative pathway of the insulin ligand and the recycling pathway of the insulin receptor. Tris(hydroxymethyl)aminomethane and other nonamphoteric amines were found to selectively impair insulin receptor recycling while leaving the insulin-degradative pathway intact. In contrast, low concentrations of the lysosomotropic agent chloroquine markedly inhibited intracellular insulin degradation but had little or no affect on the recycling of internalized receptors. Thus, we conclude: (1) that insulin dissociates from its receptor after endocytotic uptake and both receptor and ligand follow a separate intracellular pathway; and (2) that receptor recycling and insulin degradation can be selectively inhibited by Tris and chloroquine, respectively, highlighting the potential usefulness of these agents as intracellular probes in the study of receptor-ligand metabolism.