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  • 1
    ISSN: 1432-0428
    Keywords: Sulphonylurea ; rat ; insulin binding ; insulin action ; extrapancreatic effect ; glycogen synthesis ; rat hepatocytes in primary culture
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The effects of a sulphonylurea, gliquidone, on insulin binding and the insulin induced rate of glycogen synthesis, were studied in rat hepatocytes in primary culture. Hepatocytes were cultured for 48 h. During the second 24 h of this period, the hepatocytes were incubated with or without gliquidone (5 mg/l). The binding of 125I-insulin and the insulin stimulation of glycogen synthesis from 14C-glucose were measured. Gliquidone influenced neither insulin binding nor the basal rate of glycogen synthesis, but it did enhance the effect of insulin on glycogen synthesis. Responsiveness was increased by gliquidone at all insulin concentrations used (10–10,000 mU/l); at 1000 mil/l the drug increased glycogen synthesis from 310 to 430% above the basal rate. Half-maximal stimulation was reached in control cells at an insulin concentration of 95 mU/l and in gliquidone-treated cells at 94 mU/l, which indicates unchanged insulin sensitivity. Based on these experiments with cultured rat hepatocytes it appears that the extrapancreatic action of gliquidone is not mediated by an effect on insulin binding.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Insulin resistance ; lipoproteins ; liver ; insulin binding ; insulin action ; hepatoma cells
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary A lipoprotein-induced resistance to the action of insulin has been postulated. To test this hypothesis, cultured ratderived hepatoma cells, designated FAO, and human-derived hepatoma cells, designated HEP-G2, were incubated for 20 h in the presence or absence of lipoproteins; specific 125I-insulin receptor binding and labeled glucose incorporation into glycogen were then measured. Very low density lipoproteins (d 〈 1.006 g/ml) in physiologic (0.5 mg/ml) or pathophysiologic (5 mg/ml) concentrations did not modify insulin receptor binding of FAO or HEP-G2 cells. This was true for very low density lipoproteins derived from normal human, diabetic human, and streptozotocin-diabetic rat plasma. Low density lipoproteins (d=,.019–1.063g/ml) isolated from normal human plasma similarly failed to modify insulin receptor binding. Concerning insulin action, the different very low density lipoprotein preparations did not modulate either basal or insulin-stimulated glucose incorporation into glycogen of the cells. Thus, very low density lipoproteins and low density lipoproteins did not induce insulin resistance in cultured hepatoma cells either at the insulin receptor level or at the post-receptor level.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Insulin receptor isotypes ; Type 2 (non-insulin-dependent) diabetes mellitus ; insulin receptor antibody
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary The human insulin receptor exists in two isoforms (HIR-A α-subunit 719 amino acids and HIR-B α-subunit 731 amino acids) which are generated by alternative splicing of a small exon and display distinct patterns of tissue-specific expression. Using the polymerase chain reaction we have recently shown that skeletal muscle of non-diabetic individuals contains predominantly mRNA encoding HIR-A while in skeletal muscle derived from subjects with Type 2 (non-insulin-dependent) diabetes mellitus similar amounts of each mRNA are expressed. We used a polyclonal antibody which discriminates between HIR-A and HIR-B to assess the isoform expression at the protein level. The antibody showed clearly distinct displacement of insulin binding in skeletal muscle membranes of non-diabetic subjects compared to Type 2 diabetic subjects (displacement of specific 125I-insulin binding: 13 non-diabetic subjects 70.0%±14.34, 12 Type 2 diabetic subjects 32.6%±17.45). A control antibody which does not discriminate between both isoforms showed similar displacement of 125I-insulin in membranes of non-diabetic and Type 2 diabetic subjects. These data suggest that the altered expression of receptor isotype mRNA in the skeletal muscle of Type 2 diabetic subjects leads to an altered receptor isoform pattern in the plasma membrane. While skeletal muscle membranes of non-diabetic subjects contain predominantly HIR-A, membranes of Type 2 diabetic subjects show an increased level of HIR-B in addition to HIR-A.
    Type of Medium: Electronic Resource
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