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The insulin effect on glucose uptake is not sufficiently explained by a simple glucose-carrier translocation model. Recent studies rather suggest a two-step model of carrier translocation and carrier activation. We used several pharmacological tools to characterize the proposed model further. We found that inositol phosphate (IP)-oligosaccharides isolated(More)
Rat-1 fibroblasts stably overexpressing high levels of human insulin receptor were used as a model system to study the effects of hyperglycemia on insulin receptor tyrosine kinase (IRK) activity and protein kinase C (PKC) translocation in parallel in the intact cell. Glucose (10-25 mM) induced a significant reduction of IRK activity (tyrosine(More)
We have recently shown that leptin mimicks insulin effects on glucose transport and glycogen synthesis through a phosphatidylinositol-3 (PI) kinase dependent pathway in C2C12 myotubes. The aim of the present study was to identify the signalling path from the leptin receptor to the PI-3 kinase. We stimulated C2C12 myotubes with insulin (100 nmol/1, 5 min) or(More)
The insulin receptor contains in its beta-subunit a tyrosine (-) specific protein kinase. It is believed that transmission of an insulin signal across the plasma membrane of target cells of insulin action occurs through activation of this kinase, autophosphorylation of the insulin receptor beta-subunit and subsequent phosphorylation of other cellular(More)
Tumour-promoting phorbol esters have insulin-like effects on glucose transport and lipogenesis in adipocytes and myocytes. It is believed that insulin activates the glucose-transport system through translocation of glucose transporters from subcellular membranes to the plasma membrane. The aim of the present study was to investigate if phorbol esters act(More)
Recently we have shown that PKC beta1 and beta2 are able to inhibit the tyrosine kinase activity of the human insulin receptor (HIR). Now we have investigated whether a distinct PKC isoform might be involved in the inhibitory effect of TNF alpha on insulin signaling in HEK293 cells. TNF alpha induces a rapid translocation of the PKC isoform epsilon (TNF(More)
Protein kinase C (PKC) isoforms are potentially important as modulators of the insulin signalling chain and could be involved in the pathogenesis of cellular insulin resistance. We have previously shown that phorbol ester stimulated PKC beta1 and beta2 as well as tumor necrosis factor-alpha (TNFalpha) stimulated PKC epsilon inhibit human insulin receptor(More)
The mechanism of insulin signalling is not yet understood in detail. Recently, a role for inositol phosphate (IP)-oligosaccharides as second messengers transmitting the insulin signal at the post-kinase level was proposed. To evaluate this hypothesis further, we studied whether IP-oligosaccharides isolated from 'haemodialysate' have insulin-like activity.(More)
Inositol phospho-oligosaccharides (IPOs), which are released from liver membranes upon stimulation by insulin, mimic a wide spectrum of insulin effects in different cells, but not the stimulation of glucose transport. We investigated whether other insulin-sensitive tissues release glucose transport-stimulating IPOs and whether this is related to the human(More)
Insulin resistance of the skeletal muscle is a key feature of Type 2 (non-insulin-dependent) diabetes mellitus. To determine whether a decrease of glucose carrier proteins or an altered subcellular distribution of glucose transporters might contribute to the pathogenesis of the insulin resistant state, we measured glucose transporter numbers in membrane(More)