Insulin and Glucagon Receptors of Isolated Rat Hepatocytes: Comparison between Hormone Binding and Amino Acid Transport Stimulation*
- 1 July 1981
- journal article
- research article
- Published by The Endocrine Society in Endocrinology
- Vol. 109 (1), 253-261
- https://doi.org/10.1210/endo-109-1-253
Abstract
Insulin and glucagon binding was studied in isolated rat hepatocytes, and the receptor occupancy was compared to the hormonal stimulation of amino acid transport. Binding was measured at 20 and 37 C in steady state conditions using 125I-labeled iodohormone and varying concentrations of unlabeled hormone. When measured at 20 C, insulin binding was compatible with either a two-site model: a high affinity (Kd ≅ 0.6 nM) and a low affinity (Kd ≅ 12 nM) site or one class of binding sites with negatively cooperative interactions. At 20 C, the rate of dissociation of bound [125I]iodoinsulin was enhanced in the presence of unlabeled insulin, suggesting negatively cooperative interactions among insulin receptors at this temperature. At 37 C, in contrast, insulin bound predominantly to a high affinity site (Kd ≅ 0.6 nM). These data indicate that at 37 C, the low affinity site is no longer present (or detectable), and/ or there is a marked decrease in cooperative interactions at this temperature. When insulin-stimulated α-aminoisobutyric acid influx was compared to receptor occupancy at 37 C, stimulation of amino acid transport paralleled receptor occupancy at this temperature, i.e. insulin binding to the high affinity site. These results suggest that insulin action in rat hepatocytes is initiated by the interaction of the hormone with a single class of noncooperative, high affinity binding sites. Glucagon binding involved one type of noncooperative binding sites (Kd ≅ 5 nM) at both 20 and 37 C. There was no direct proportionality between glucagon binding and glucagon stimulation of amino acid transport, with a half-maximal effect occurring at about 20% total receptor occupancy. The data indicate that the high coupling efficiency which has been reported for glucagon binding and proximal events of glucagon action (e.g. cAMP accumulation) is also observed for a more distal effect, such as stimulation of amino acid transport.Keywords
This publication has 6 references indexed in Scilit:
- Evidence Supporting a Two-Receptor Model for Insulin Binding by Cultured Embryonic Heart Cells*Endocrinology, 1980
- Ouabain-resistant hyperpolarization induced by insulin in aggregates of embryonic heart cells.Proceedings of the National Academy of Sciences, 1980
- Insulin receptors in isolated rat hepatocytes. Reassessment of binding properties and observations of the inactivation of insulin at 37 degrees C.Journal of Biological Chemistry, 1978
- The effects of glucagon, catecholamines, and the calcium ionophore A23187 on the phosphorylation of rat hepatocyte cytosolic proteins.Journal of Biological Chemistry, 1978
- Effects of glucagon and insulin on cytoplasmic protein phosphorylation in hepatocytesJournal of Biological Chemistry, 1978
- Binding of 125I-labeled glucagon and glucagon-stimulated accumulation of adenosine 3‘:5‘-monophosphate in isolated intact rat hepatocytes. Evidence for receptor heterogeneity.Journal of Biological Chemistry, 1978