| 1. |
- Goodyear, Laurie J.L, et al.
(författare)
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Glucoseingestion causes GLUT4 translocation in human skeletal muscle
- 1996
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 45:8, s. 1051-1056
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Tidskriftsartikel (refereegranskat)abstract
- In humans, ingestion of carbohydrates causes an increase in blood glucose concentration, pancreatic insulin release, and increased glucose disposal into skeletal muscle. The underlying molecular mechanism for the increase in glucose disposal in human skeletal muscle after carbohydrate ingestion is not known. We determined whether glucoseingestion increases glucose uptake in human skeletal muscle by increasing the number of glucose transporter proteins at the cell surface and/or by increasing the activity of the glucose transporter proteins in the plasma membrane. Under local anesthesia, approximately 1 g of vastus lateralis muscle was obtained from six healthy subjects before and 60 min after ingestion of a 75-g glucose load. Plasma membranes were isolated from the skeletal muscle and used to measure GLUT4 and GLUT1 content and glucosetransport in plasma membrane vesicles. Glucose ingestion increased the plasma membrane content of GLUT4 per gram muscle (3,524 +/- 729 vs. 4,473 +/- 952 arbitrary units for basal and 60 min, respectively; P < 0.005). Transporter-mediated glucosetransport into plasma membrane vesicles was also significantly increased (130 +/- 11 vs. 224 +/- 38 pmol.mg-1.s-1; P < 0.017), whereas the calculated ratio of glucose transport to GLUT4, an indication of transporter functional activity, was not significantly increased 60 min after glucose ingestion (2.3 +/- 0.4 vs. 3.0 +/- 0.5 pmol.GLUT4 arbitrary units-1.s-1; P < 0.17). These results demonstrate that oral ingestion of glucose increases the rate of glucose transport across the plasma membrane and causes GLUT4 translocation in human skeletal muscle. These findings suggest that under physiological conditions the translocation of GLUT4 is an important mechanism for the stimulation of glucose uptake in human skeletal muscle.
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| 2. |
- Gromada, J, et al.
(författare)
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Glucagon-like peptide I increases cytoplasmic calcium in insulin-secreting beta TC3-cells by enhancement of intracellular calcium mobilization
- 1995
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 44:7, s. 767-774
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Tidskriftsartikel (refereegranskat)abstract
- In the insulin-secreting beta-cell line beta TC3, stimulation with 11.2 mmol/l glucose caused a rise in the intracellular free Ca2+ concentration ([Ca2+]i) in only 18% of the tested cells. The number of glucose-responsive cells increased after pretreatment of the cells with glucagon-like peptide I (GLP-I)(7-36)amide and at 10(-11) mol/l; 84% of the cells responded to glucose with a rise in [Ca2+]i. GLP-I(7-36)amide induces a rapid increase in [Ca2+]i only in cells exposed to elevated glucose concentrations (> or = 5.6 mmol/l). The action of GLP-I(7-36)amide and forskolin involved a 10-fold increase in cytoplasmic cAMP concentration and was mediated by activation of protein kinase A. It was not associated with an effect on the membrane potential but required some (small) initial entry of Ca2+ through voltage-dependent L-type Ca2+ channels, which then produced a further increase in [Ca2+]i by mobilization from intracellular stores. The latter effect reflected Ca(2+)-induced Ca2+ release and was blocked by ryanodine. Similar increases in [Ca2+]i were also observed in voltage-clamped cells, although there was neither activation of a background (Ca(2+)-permeable) inward current nor enhancement of the voltage-dependent L-type Ca2+ current. These observations are consistent with GLP-I(7-36) amide inducing glucose sensitivity by promoting mobilization of Ca2+ from intracellular stores. We propose that this novel action of GLP-I(7-36)amide represents an important factor contributing to its insulinotropic action.
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| 3. |
- Salehi, S Albert, et al.
(författare)
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The pseudotetrasaccharide acarbose inhibits pancreatic islet glucan-1,4-alpha-glucosidase activity in parallel with a suppressive action on glucose-induced insulin release
- 1995
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 44:7, s. 830-836
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Tidskriftsartikel (refereegranskat)abstract
- The pseudotetrasaccharide acarbose, previously known as a potent inhibitor of intestinal alpha-glucoside hydrolases, was investigated with regard to its influence on islet lysosomal enzyme activities and the insulin secretory processes. We observed that acarbose was a potent inhibitor of mouse islet lysosomal acid glucan-1,4-alpha-glucosidase activity, EC50 approximately 5 mumol/l, as well as of acid alpha-glucosidase activity. In contrast, acarbose did not influence other lysosomal enzyme activities such as acid phosphatase and N-acetyl-beta-D-glucosaminidase. Neutral alpha-glucosidase (endoplasmic reticulum) was only moderately inhibited in homogenate and was unaffected in intact islets. Incubation of isolated mouse islets with acarbose revealed that the pseudotetrasaccharide was a strong inhibitor of glucose-induced insulin secretion, EC50 approximately 500 nmol/l, and a significant inhibition was already observed at a concentration of acarbose as low as 100 nmol/l. The acarbose analogue maltotetrose did not influence either glucose-induced insulin release or islet lysosomal enzyme activities. Further, acarbose as well as two other alpha-glucoside hydrolase inhibitors, the deoxynojirimycin derivatives miglitol and emiglitate, did not affect islet glucose oxidation at low or high glucose levels. Acarbose also inhibited insulin release induced by the sulfonylurea glibenclamide, whereas insulin secretion stimulated by the cholinergic muscarinic agonist carbachol or the phosphodiesterase inhibitor isobutylmethylxanthine was unaffected by the drug. Moreover, complementary in vivo experiments showed that pretreatment of mice with acarbose to allow for endocytosis of the compound markedly suppressed the insulin secretory response to an intravenous glucose load.(ABSTRACT TRUNCATED AT 250 WORDS)
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| 4. |
- Sanjeevi, C. B., et al.
(författare)
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Polymorphic amino acid variations in HLA-DQ are associated with systematic physical property changes and occurrence of IDDM
- 1995
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 44:1, s. 125-131
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Tidskriftsartikel (refereegranskat)abstract
- The association between human leukocyte antigen (HLA) insulin-dependent diabetes was studied in a large population-based investigation using genotyping of 425 new-onset patients, 0-14 years of age, and 367 matched control subjects. As many as 97% of patients compared with 75% of control subjects were positive for one or several of DQA1*0301, DQA1*0501, DQB1*0302, or DQB1*0201. Asp-57 DQB was present among 28% of patients, indicating that this residue alone does not confer protection. Combining Asp- 57 DQB1 with either Arg-52 DQA1 or Leu-69 DQA1 did not explain susceptibility or protection either. DQA1*0301-DQB1*0302 (DQS) and DQA1*0301-DQB1*0301 (DQ7) are identical except for four amino acid substitutions in the β- chain, but DQ8 was positively (odds ratio 8.07; P < 0.001) and DQ7 negatively (odds ratio 0.38; P < 0.001) associated with the disease. Molecular modeling was used to determine whether physicochemical properties such as steric factors and surface electrostatic potentials also differ in a systematic way for various DQ molecules. Amino acids were substituted systematically at the four polymorphic sites, and the solvent-accessible surfaces and electrostatic potentials were computed for each molecule. Dramatic alterations in electrostatic potential were seen for double substitutions at position 45 (G45E) and 57 (A57D) of DQB1. The variation of physicochemical properties due to polymorphic substitutions may be significant to the mechanism of HLA-DQ association with insulin-dependent diabetes, via the effect these property variations have on peptide antigen binding selectivity and subsequent interactions with specific T-cell receptors.
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| 5. |
- Mulder, Hindrik, et al.
(författare)
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Hormone-sensitive lipase, the rate-limiting enzyme in triglyceride hydrolysis, is expressed and active in beta-cells
- 1999
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Ingår i: Diabetes. - 1939-327X. ; 48:1, s. 228-232
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Tidskriftsartikel (refereegranskat)abstract
- Triglycerides in the beta-cell may be important for stimulus-secretion coupling, through provision of a lipid-derived signal, and for pathogenetic events in NIDDM, where lipids may adversely affect beta-cell function. In adipose tissues, hormone-sensitive lipase (HSL) is rate-limiting in triglyceride hydrolysis. Here, we investigated whether this enzyme is also expressed and active in beta-cells. Northern blot analysis and reverse transcription-polymerase chain reaction demonstrated that HSL is expressed in rat islets and in the clonal beta-cell lines INS-1, RINm5F, and HIT-T15. Western blot analysis identified HSL in mouse and rat islets and the clonal beta-cells. In mouse and rat, immunocytochemistry showed a predominant occurrence of HSL in beta-cells, with a presumed cytoplasmic localization. Lipase activity in homogenates of the rodent islets and clonal beta-cells constituted 2.1 +/- 0.6% of that in adipocytes; this activity was immunoinhibited by use of antibodies to HSL. The established HSL expression and activity in beta-cells offer a mechanism whereby lipids are mobilized from intracellular stores. Because HSL in adipocytes is activated by cAMP-dependent protein kinase (PKA), PKA-regulated triglyceride hydrolysis in beta-cells may participate in the regulation of insulin secretion, possibly by providing a lipid-derived signal, e.g., long-chain acyl-CoA and diacylglycerol.
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| 6. |
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