Insulin receptors in rat insulin secreting β-cells

M. Buscema, F. Giorgino, F. Purrello, L. Frittitta, A. Costantino, G. Grasso, V. Trischitta

Research output: Contribution to journalArticlepeer-review

Abstract

The content and functional characteristics of insulin receptors were studied in cultured rat insulinoma RINm5F cells. Insulin receptors content, as measured by a specific radioimmunoassay, was 9.4 ± 2.1 ng/106 cells (mean ± SE). The α-subunit insulin receptor function was investigated by 125I-insulin binding studies. The calculated binding affinity was lower in intact cells (IC50 = 0.7 nM) than in a cell-free systems such as purified plasma membranes (IC50 = 0.25 nM) or wheat germ agglutinin-agarose (WGA) purified receptors (IC50 = 0.10 nM). Similarly to typical insulin target cells, after binding to cell surface receptors, insulin is internalized into the intracellular compartment. The proportion of bound 125I-insulin that is internalized is temperature-dependent being higher at 37°C than at 4°C (60 ± 5.7% and 4 ± 0.8%, respectively). Moreover, insulin was able to down regulate cell surface insulin receptors with a half maximal effect at 1 nM. The β-subunit insulin receptor function was investigated by studying insulin stimulated receptor autophosphorylation and its tyrosine kinase activity toward the exogenous substrate. Poly-Glu: Tyr 4:1. The effect of insulin was dose-dependent for both these activities with a half maximal effect at 1 nM insulin. Rat insulinoma RINm5F cells, therefore, have a significant number of functioning insulin receptors fully capable to mediate insulin biological activity. Since in preliminary studies we observed that also freshly isolated rat β-cells have a similar insulin receptor content (11.7 ± 3.1 ng/106 cells) than RINm5F cells and that these insulin receptors have an insulin stimulable tyrosine kinase activity, these data are consistent with a potential role of the insulin receptor in the biology and function of pancreatic β-cells.

Original languageEnglish
Pages (from-to)197-203
Number of pages7
JournalDiabetes, Nutrition and Metabolism - Clinical and Experimental
Volume7
Issue number4
Publication statusPublished - 1994

Keywords

  • Insulin receptor
  • Insulin receptor affinity
  • Insulin receptor tyrosine kinase activity
  • Insulin secreting β-cells

ASJC Scopus subject areas

  • Food Science
  • Endocrinology
  • Medicine (miscellaneous)
  • Endocrinology, Diabetes and Metabolism
  • Internal Medicine

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