The role of insulin dissociation from its endosomal receptor in insulin degradation.

Mechanisms that terminate signals from activated receptors have potential to influence the magnitude and nature of cellular responses to insulin. The aims of this study were to determine in rat liver endosomes (the subcellular site of insulin signal termination) whether dissociation of insulin from its receptor was a pre-requisite for ligand degradation and whether the state of receptor phosphorylation influenced the dissociation and hence endosomal degradation of insulin and/or receptor recycling. Following in vivo administration of 125I-[A14]-insulin or analogues (native, X10 or H2, relative binding affinities 1:7:67) livers were removed and endosomes prepared.

Chloroquine extends the lifetime of the activated insulin receptor complex in endosomes.

Insulin signal transduction, initiated by binding of insulin to its receptor at the plasma membrane, activates the intrinsic receptor tyrosine kinase and leads to internalization of the activated ligand-receptor complex into endosomes. This study addresses the role played by the activated insulin receptor within hepatic endosomes and provides evidence for its central role in insulin-stimulated events in vivo. Rats were treated with chloroquine, an acidotrophic agent that has been shown previously to inhibit endosomal insulin degradation, and then with insulin.

An evaluation of the cross-linking model for the interaction of insulin with its receptor.

The cross-linking model for insulin receptor interactions, in which a single insulin molecule may form a cross-link between an insulin receptor's alpha-subunits, has been expressed as a formal compartmental model and subjected to a systematic analysis, examining a number of predictions that have been made for this model. The kinetic parameters for the model were obtained by matching data from insulin receptor equilibrium binding studies and rates of formation of the insulin receptor complex. This analytical study has allowed a clear description of the kinetics of the ligand receptor complexes involved in such a mechanism.

Altered regulation of hepatic glucose output in the male offspring of protein-malnourished rat dams.

Offspring of protein-malnourished rat dams have permanent alterations in hepatic enzyme activities associated with glucose homeostasis. Hormonal control of hepatic glucose output (HGO) was studied in male offspring of dams fed either a 20% (control) or 8% (low protein) protein diet during pregnancy and lactation. Glucagon (210 pM) stimulated HGO significantly more (P < 0.

Chloroquine augments the binding of insulin to its receptor.

The effect of chloroquine on the interaction of insulin with its receptor has been investigated under both equilibrium and non-equilibrium conditions. Chloroquine was found to augment insulin binding in a pH-dependent manner between pH 6.0 and pH 8.