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  • 1
    ISSN: 1432-1424
    Keywords: Rat insulinoma cell line, CRI-G1 ; Cyclic nucleotide regulation ; Calcium-activated nonselective cation channel ; Patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The regulation of a calcium-activated nonselective cation (Ca-NS+) channel by analogues of cyclic AMP has been investigated in the rat insulinoma cell line, CRI-G1. The activity of the channel is modulated by cyclic AMP in a complex way. In the majority of patches (83%) tested concentrations of cyclic AMP of 10 μm and above cause an inhibition of channel activity which is immediately reversible on washing. In contrast, lower concentrations of cyclic AMP, between 0.1 and 1.0 μm, produce a transient activation of channel activity in most patches (63%) tested. One group of analogues, including N6-monobutyryl cyclic AMP and N6, 2′-O-dibutyryl cyclic AMP reduced the activity of the Ca-NS+ channel at all concentrations tested and 2′-O-Monobutyryl cyclic AMP produced inhibition in all patches tested except one, at all concentrations. A second group produced dual concentration-dependent effects on Ca-NS+, low concentrations stimulating and high concentrations inhibiting channel activity. 6-Chloropurine cyclic AMP and 8-bromo cyclic AMP produced effects similar to those of cyclic AMP itself. In contrast, 8-[4-chlorophenylthio] cyclic AMP also showed a dual action, but with a high level of activation at all concentrations tested up to 1mm. Ca-NS+ channel activity was also predominantly activated by low concentrations of Sp-cAMPS. The activating effects of both Sp-cAMPS and cyclic AMP are antagonized by Rp-cAMPS, which by itself only produced a weak inhibition of Ca-NS+ channel activity even at concentrations of 10 μm and above. The results are discussed in terms of a model in which cyclic AMP, and other cyclic nucleotides, modulate the activity of the Ca-NS+ channel by binding to two separate sites.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Springer
    The journal of membrane biology 141 (1994), S. 101-112 
    ISSN: 1432-1424
    Keywords: Rat insulinoma cell line ; CRI-G1 ; Nucleotide regulation ; Calcium-activated nonselective cation channel ; Patch clamp
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Chemistry and Pharmacology
    Notes: Abstract The nucleotide regulation of a calcium-activated nonselective cation (Ca-NS+) channel has been investigated in the rat insulinoma cell line CRI-G1. The activity of the channel is reduced by both AMP and ADP (1–100 μm) in a concentration-dependent manner, with AMP being more potent than ADP. At lower concentrations (0.1–5 μm), both ADP and AMP activate the channel in some patches. Examination of the nucleotide specificity of channel inhibition indicates a high selectivity for AMP over the other nucleotides tested with a rank order of potency of AMP 〉 UMP 〉 CMP ≥GMP. Cyclic nucleotides also modulate channel activity in a complex, concentration-dependent way. Cyclic AMP exhibits a dual effect, predominantly increasing channel activity at low concentrations (0.1–10 μm) and reducing it at higher concentrations (100 μm and 1 mm). Specificity studies indicate that the cyclic nucleotide site mediating inhibition of channel activity exhibits a strong preference for cyclic AMP over cyclic GMP, with cyclic UMP being almost equipotent with cyclic AMP. Cyclic IMP and cyclic CMP are not active at this site. The cyclic nucleotide site mediating activation of the channel shows much less nucleotide specificity than the inhibitory site, with cyclic AMP, cyclic GMP and cyclic IMP being almost equally active.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-0428
    Keywords: Indirect two-site immunoradiometric assay ; human proinsulin ; insulin ; C-peptide ; diabetes ; insulinoma
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary An indirect two-site immunoradiometric assay is described for the measurement of human proinsulin in plasma. Polyethylene tubes coated with purified guinea-pig antibodies to insulin were used to extract proinsulin and insulin from plasma. Rabbit antibody to human C peptide was then added to react with the C-peptide moiety of the bound proinsulin. The uptake of this antibody was measured by the subsequent binding of125I-sheep antibody to rabbit IgG. The binding of radioactivity to the tubes was a function of the proinsulin concentration in the sample. The sensitivity of the assay was 0.006 pmol/ml. Only 200 μl of plasma was required in the assay and the125I-labelled antibody was produced from readily available reagents. The polyethylene tubes remained stable for at least 5 months after coating. The mean fasting proinsulin level was 0.009 pmol/ml in sixteen normal subjects and 0.025 pmol/ml in twelve maturity onset diabetics. Oral glucose produced an 8 fold increase in proinsulin concentration but a decline in the plasma proinsulin/insulin molar ratio. Four patients with insulinoma had extremely elevated proinsulin levels and proinsulin/insulin ratios.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1432-0428
    Keywords: Proinsulin ; insulin ; C-peptide ; identical twins ; Type 1 (insulin-dependent) diabetes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Glucose tolerance and insulin secretion were studied in two groups of non-diabetic identical twins of recently-diagnosed Type 1 (insulin-dependent) diabetic patients: (1) a group of 5 twins with islet cell antibodies, and (2) a group of 6 twins without. Despite similar fasting glucose, insulin and C-peptide concentrations both groups of twins had significantly higher fasting proinsulin concentrations than the control group (p〈0.05). The twins with complement-fixing islet cell antibodies had reduced glucose tolerance and clearance, whilst the twins without islet cell antibodies did not. Neither group of twins showed any abnormality in insulin, C-peptide or proinsulin response to oral or intravenous glucose. We conclude that increased fasting proinsulin levels precede abnormalities of insulin secretion, and are an early indication of minor B-cell damage in these twins irrespective of their risk of developing diabetes.
    Type of Medium: Electronic Resource
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  • 5
    ISSN: 1432-0428
    Keywords: Key words Non-insulin-dependent diabetes mellitus ; vitamin D ; vitamin D deficiency ; total insulin ; specific insulin ; proinsulin ; 32 ; 33 split proinsulin ; C-peptide ; glucose intolerance.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Vitamin D deficiency reduces insulin secretion and still occurs in East London Asians in whom the prevalence of diabetes mellitus is at least four times that of Caucasians. Vitamin D status was assessed in 44 of 65 non-diabetic subjects ’at risk' of diabetes (spot blood glucose level 〉 6.0 mmol/l 〈 2 h post cibum, or 〉 4.6 mmol/l 〉 2 h post cibum on two separate occasions) and in 15 of 60 age and sex-matched ’low-risk' control subjects who attended for oral glucose tolerance test (OGTT) after screening of 877 omnivorous subjects not known to have diabetes. It was found that 95 % of at-risk and 80 % of low-risk subjects were vitamin D deficient (serum 25-hydroxy-vitamin D 〈 11 ng/ml). Diabetes was present in 16, impaired glucose tolerance in 12 and normoglycaemia in 19 at-risk subjects, impaired glucose tolerance in 2, and normoglycaemia in 13 low-risk subjects. Correlations of 30-min OGTT blood glucose, specific insulin and C-peptide levels with 25-hydroxy-vitamin D concentrations in 44 at-risk subjects were −0.31 (p = 0.04), 0.59 (p = 0.0001) and 0.44 (p = 0.006). In 15 ’not-at-risk' subjects 30-min OGTT specific insulin and C-peptide levels correlated with 25-hydroxy-vitamin D, r = 0.39 (p = 0.04) and 0.16 (p = 0.43), respectively. Serum alkaline phosphatase concentration was higher in at-risk than not-at-risk subjects (59.6 vs 46.5 IU/l, p = 0.012); corrected calcium concentrations were comparable (2.38 vs 2.39 mmol/l, p = 0.7). Following treatment with 100,000 IU vitamin D by i. m. injection, specific insulin, C-peptide [30 min on OGTT] and 25-hydroxy-vitamin D concentrations had risen 8–12 weeks later [means ± SD] from 57 ± 62 to 96.2 ± 82.4 mU/l [p = 0.0017], 1.0 ± 0.4 to 1.7 ± 0.8 pmol/ml [p = 0.0001] and 3.6 ± 1.8 to 13.5 ± 7.4 ng/ml [p = 0.0001], (but not to low-risk group values of 179 ± 89 mU/l, 2.7 ± 1.14 pmol/ml and 8.16 ± 6.4 ng/ml), respectively. Both total serum alkaline phosphatase and corrected calcium concentrations rose following vitamin D treatment in the at-risk subjects by 11.1 ± 8.22 (from 44 to 55 IU/l) and 0.15 ± 0.18, (2.43 to 2.57 mmol/l), respectively (p = 0.004). Abnormal glucose tolerance was unchanged by vitamin D treatment. The value of early and sustained repletion with vitamin D in diabetes prophylaxis should be examined in communities where vitamin D depletion is common. [Diabetologia (1995) 38: 1239–1245]
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1432-0428
    Keywords: Non-insulin-dependent diabetes mellitus ; vitamin D ; vitamin D deficiency ; total insulin ; specific insulin ; proinsulin ; 32,33 split proinsulin ; C-peptide ; glucose intolerance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Medicine
    Notes: Summary Vitamin D deficiency reduces insulin secretion and still occurs in East London Asians in whom the prevalence of diabetes mellitus is at least four times that of Caucasians. Vitamin D status was assessed in 44 of 65 non-diabetic subjects ‘at risk’ of diabetes (spot blood glucose level 〉6.0 mmol/l 〈2 h post cibum, or 〉4.6 mmol/l 〉2 h post cibum on two separate occasions) and in 15 of 60 age and sex-matched ‘low-risk’ control subjects who attended for oral glucose tolerance test (OGTT) after screening of 877 omnivorous subjects not known to have diabetes. It was found that 95% of at-risk and 80% of low-risk subjects were vitamin D deficient (serum 25-hydroxy-vitamin D 〈11 ng/ml). Diabetes was present in 16, impaired glucose tolerance in 12 and normoglycaemia in 19 at-risk subjects, impaired glucose tolerance in 2, and normoglycaemia in 13 low-risk subjects. Correlations of 30-min OGTT blood glucose, specific insulin and C-peptide levels with 25-hydroxy-vitamin D concentrations in 44 at-risk subjects were −0.31 (p=0.04), 0.59 (p=0.0001) and 0.44 (p=0.006). In 15 ‘not-at-risk’ subjects 30-min OGTT specific insulin and C-peptide levels correlated with 25-hydroxy-vitamin D, r=0.39 (p=0.04) and 0.16 (p=0.43), respectively. Serum alkaline phosphatase concentration was higher in at-risk than not-at-risk subjects (59.6 vs 46.5 IU/l, p=0.012); corrected calcium concentrations were comparable (2.38 vs 2.39 mmol/l, p=0.7). Following treatment with 100,000 IU vitamin D by i.m. injection, specific insulin, C-peptide [30 min on OGTT] and 25-hydroxy-vitamin D concentrations had risen 8–12 weeks later [means±SD] from 57±62 to 96.2±82.4 mU/l [p=0.0017], 1.0±0.4 to 1.7±0.8 pmol/ml [p=0.0001] and 3.6±1.8 to 13.5±7.4 ng/ml [p=0.0001], (but not to low-risk group values of 179±89 mU/l, 2.7±1.14 pmol/ml and 8.16±6.4 ng/ml), respectively. Both total serum alkaline phosphatase and corrected calcium concentrations rose following vitamin D treatment in the at-risk subjects by 11.1±8.22 (from 44 to 55 IU/l) and 0.15±0.18, (2.43 to 2.57 mmol/l), respectively (p=0.004). Abnormal glucose tolerance was unchanged by vitamin D treatment. The value of early and sustained repletion with vitamin D in diabetes prophylaxis should be examined in communities where vitamin D depletion is common.
    Type of Medium: Electronic Resource
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