Binding and Degradation of Insulin by Isolated Renal Cortical Tubules*

Publisher Website
Google Scholar
Abstract
Binding and degradation of monoiodinated [125I]insulin by isolated tubules of rat kidney cortex were studied. Binding and degradation of insulin were dependent on temperature and duration of incubation as well as on the tubule concentration. Degradation was minimized by the use of low to moderate tubule concentrations and an incubation temperature of 22 C. Increasing concentrations of unlabeled insulin (0.1–1000 nm added in the incubation medium) decreased [125I]insulin binding in a dose-dependent fashion. Analysis of the data was consistent either with receptors with different affinities or with a single class of receptors, which demonstrates negative cooperativity. Parathyroid hormone and other peptide hormones did not affect [125I]insulin binding to tubules. Approximately 70–75% of bound [125I]insulin could be dissociated by the subsequent addition of excess unlabeled insulin. Insulin binding preceded degradation, and preincubation of tubules with trypsin abolished binding and degradation of insulin. These data indicate the presence of specific insulin receptors in renal cortical tubules and suggest that binding of insulin to its receptors may be important for insulin degradation. The interaction between insulin binding and degradation may underlie some physiological effects of insulin on renal function and may play a role in the renal metabolism of insulin. (Endocrinology106: 655, 1980)