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  • 1
    ISSN: 1432-0428
    Keywords: Glucose transporter ; glucose transporter mRNA ; aging
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary To elucidate the cellular mechanisms of glucose intolerance associated with aging, both the protein and mRNA levels of glucose transporter isoforms were studied in the various tissues of young (7-week-old) and aged (20-monthold) rats. GluT4 (adipose/muscle-type glucose transporter) protein, which is specifically expressed in insulin-responsive tissues, was selectively decreased per milligramme of cellular membrane protein in both the epididymal fat tissues and the gastrocnemius muscle of the aged rats compared with the young rats. When the changes in total cellular membranes per gramme of tissue are taken into account, a further decrease in GluT4 protein per gramme of tissue was observed in the tissues of the aged rats compared with the young rats. The decreased amount of GluT4 protein in the fat tissues of the aged rats is probably due to the decreased protein synthesis rather than the stability, since GluT4 mRNA/μg of cellular total RNA was also decreased. In contrast, GluT4 mRNA in the gastrocnemius muscle was rather increased and a ratio of GluT4 protein/GluT4 mRNA was decreased by 70% in the aged rats, suggesting that the translational efficiency and/or stability of GluT4 protein is decreased in the skeletal muscle of the aged rats compared with the young rats. GluT2 (livertype glucose transporter) protein and mRNA in the liver were also decreased in the aged rats, while no apparent decrease in GluT1 (HepG2/brain-type glucose transporter) protein/mg of cellular membrane protein was observed in the skeletal muscle and fat tissues of the aged rats compared with the young rats. Thus, the tissue and isoform-specific alterations of glucose transporter expression are associated with aging and may contribute to glucose intolerance observed with aging.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1432-0428
    Keywords: Potassium channel ; inward rectifier ; non-insulin-dependent diabetes mellitus ; genetics ; single strand conformation polymorphism
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Ligand gated potassium channels, such as the ATP-regulated potassium channel, play crucial roles in coupling of stimuli to insulin secretion in pancreatic beta cells. Mutations in the genes might lead to the insulin secretory defects observed in patients with non-insulin-dependent diabetes mellitus (NIDDM). We isolated a cDNA encoding a putative subunit of a ligand gated potassium channel from a human islet cDNA library. The channel, which we designated hiGIRK2, appeared to be an alternative spliced variant and a human homologue of recently reported mbGIRK2, KATP-2/BIR1. Transcripts were detected in human brain and pancreas, but not in other tissues including cardiac muscle. The sizes of transcripts in the pancreas differed from those in the brain, suggesting tissue-specific alternative splicing and possible isoforms. We then isolated human genomic clones, determined the complete genomic structure and localized the gene to chromosome 21 (21q22). The gene was comprised of four exons and the protein was encoded by three exons. The entire coding region of the hiGIRK2 gene was scanned by polymerase chain reaction-single strand conformation polymorphism analysis in 80 Japanese NIDDM patients. We found five nucleotide substitutions; three were silent mutations of the third base of codons, one in the first intron, 9 bases upstream of exon 2, and one in the 3′-untranslated region. We conclude that mutations in the gene encoding MGIRK2, a (subunit of) ligand gated potassium channel, is not a major determinant of the susceptibility to NIDDM in Japanese.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Clonal beta-cell line ; insulin secretion ; glucose transport ; glucose phosphorylation ; glucose utilization
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glucose-stimulated insulin secretion, glucose transport, glucose phosphorylation and glucose utilization have been characterized in the insulinoma cell line MIN6, which is derived from a transgenic mouse expressing the large T-antigen of SV40 in pancreatic beta cells. Glucose-stimulated insulin secretion occurred progressively from 5 mmol/l glucose, reached the maximal level approximately seven-fold above the basal level at 25 mmol/l, and remained at this level up to 50 mmol/l. Glucose transport was very rapid with the half-maximal uptake of 3-O-methyl-d-glucose being reached within 15 s at 22 °C. Glucose phosphorylating activity in the cell homogenate was due mainly to glucokinase; the Vmax value of glucokinase activity was estimated to be 255±37 nmol·h−1·mg protein−1, constituting approximately 80% of total phosphorylating activity, whereas hexokinase activity constituted less than 20%. MIN6 cells exhibited mainly the high Km component of glucose utilization with a Vmax of 289±18 nmol·h−1·mg protein−1. Thus, glucose utilization quantitatively and qualitatively reflected glucose phosphorylation in MIN6 cells. In contrast, MIN7 cells, which exhibited only a small increase in insulin secretion in response to glucose, had 4.7-fold greater hexokinase activity than MIN6 cells with a comparable activity of glucokinase. These characteristics in MIN6 cells are very similar to those of isolated islets, indicating that this cell line is an appropriate model for studying the mechanism of glucose-stimulated insulin secretion in pancreatic beta cells.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0428
    Keywords: Keywords Potassium channel ; inward rectifier ; non-insulin-dependent diabetes mellitus ; genetics ; single strand conformation polymorphism.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Ligand gated potassium channels, such as the ATP-regulated potassium channel, play crucial roles in coupling of stimuli to insulin secretion in pancreatic beta cells. Mutations in the genes might lead to the insulin secretory defects observed in patients with non-insulin-dependent diabetes mellitus (NIDDM). We isolated a cDNA encoding a putative subunit of a ligand gated potassium channel from a human islet cDNA library. The channel, which we designated hiGIRK2, appeared to be an alternative spliced variant and a human homologue of recently reported mbGIRK2, KATP-2/BIR1. Transcripts were detected in human brain and pancreas, but not in other tissues including cardiac muscle. The sizes of transcripts in the pancreas differed from those in the brain, suggesting tissue-specific alternative splicing and possible isoforms. We then isolated human genomic clones, determined the complete genomic structure and localized the gene to chromosome 21 (21q22). The gene was comprised of four exons and the protein was encoded by three exons. The entire coding region of the hiGIRK2 gene was scanned by polymerase chain reaction-single strand conformation polymorphism analysis in 80 Japanese NIDDM patients. We found five nucleotide substitutions; three were silent mutations of the third base of codons, one in the first intron, 9 bases upstream of exon 2, and one in the 3 ′-untranslated region. We conclude that mutations in the gene encoding hiGIRK2, a (subunit of) ligand gated potassium channel, is not a major determinant of the susceptibility to NIDDM in Japanese. [Diabetologia (1996) 39: 447–452]
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0428
    Keywords: Key words Insulin secretion impairment, secondary sulphonylurea failure, mitochondria, maternal inheritance.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Mutations in the mitochondrial gene were recently identified in a large pedigree of diabetes mellitus and deafness. As the mitochondrial gene is maternally inherited, Japanese diabetic patients whose mothers were also diabetic were screened, using peripheral leucocytes, for an A to G transition at nucleotide pair 3243 of the mitochondrial gene, a tRNALeu(UUR) mutation. This mutation was identified in four pedigrees from among 300 unrelated patients who were screened. Diabetes co-segregated with the mutation, except in one young subject, and was maternally inherited. The apparent onset of disease occurred between 11 and 68 years of age. Some of the affected members developed hearing impairment and congestive heart failure due to cardiomyopathy, though generally long after the onset of diabetes, and these patients had therefore not been diagnosed as having a specific form of diabetes. The duration of sulphonylurea treatment was not more than 8 years in these pedigrees and affected members were prone to progression to insulin-requiring diabetes. Thus, these patients were secondary sulphonylurea failures. Long-term follow-up revealed that the underlying disorder in affected members is a progressive impairment of insulin secretion. Some were initially diagnosed as having IDDM based on an apparent acute onset in youth and the clinical severity of their diabetes. Others were regarded as having MODY with an aggressive course. The mitochondrial gene mutation or diabetes is not transmitted to all offspring of the affected mothers. In conclusion, a mitochondrial tRNALeu(UUR) gene mutation accounts for slightly more than 1 % of diabetic patients with maternally inherited disease and manifests a wide range of diabetic phenotypes, from the NIDDM phenotype to IDDM, in Japanese. [Diabetologia (1994) 37: 504–510]
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0428
    Keywords: Keywords Insulin sensitiser ; isoxazolidinedione ; JTT-501 ; GLUT4 ; phosphatidylinositol 3-kinase ; high fat diet ; adipocyte.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary JTT-501 is an insulin-sensitising compound with an isoxazolidinedione rather than a thiazolidionedione structure. Sprague-Dawley rats fed a high fat diet for 2 weeks were used as an animal model of insulin resistance, and JTT-501 was administered for the final week of the diet. An euglycaemic glucose clamp study showed that the glucose infusion rate (GIR) required to maintain euglycaemia was 57 % lower in rats fed a high fat diet than in control rats, and that JTT-501 treatment restored the reduction in GIR produced by the high fat diet. To explain the mechanisms underlying the effects of a high fat diet and JTT-501 treatment, epididymal fat pads were excised and used in the analysis of insulin action. The high fat diet caused: (1) a 58 % decrease in insulin receptor substrate-1 (IRS-1) content with a 58 % decrease in IRS-1 tyrosine phosphorylation; (2) reductions of 56 % and 73 % respectively in insulin-induced maximal PI 3-kinase activation in anti-phosphotyrosine and anti-IRS-1 antibody immunoprecipitates; (3) a 46 % reduction in the glucose transporter protein, GLUT4 content and, consequently, (4) severely impaired insulin-induced GLUT4 translocation to the plasma membrane and glucose uptake in adipocytes. JTT-501 treatment restored appreciably the protein content and tyrosine phosphorylation level of IRS-1. Insulin-stimulated PI 3-kinase activation was also restored in anti-phosphotyrosine and anti-IRS-1 antibody immunoprecipitates. As reflected by these improvements in insulin signalling, JTT-501 treatment improved considerably insulin-induced GLUT4 translocation to the plasma membrane as well as insulin-induced glucose uptake. However, JTT-501 had no effect on the decrease in GLUT4 content produced by the high fat diet. These observations suggest that JTT-501 enhances insulin signalling and may be effective in reducing insulin resistance. [Diabetologia (1998) 41: 400–409]
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    s.l. ; Stafa-Zurich, Switzerland
    Journal of metastable and nanocrystalline materials Vol. 11 (June 2001), p. 1-8 
    ISSN: 1422-6375
    Source: Scientific.Net: Materials Science & Technology / Trans Tech Publications Archiv 1984-2008
    Topics: Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
    Type of Medium: Electronic Resource
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  • 8
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Amsterdam : Elsevier
    Biochemical and Biophysical Research Communications 190 (1993), S. 1149-1155 
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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  • 10
    ISSN: 0006-291X
    Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002
    Topics: Biology , Chemistry and Pharmacology , Physics
    Type of Medium: Electronic Resource
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