| 1. |
- Lund, P E, et al.
(författare)
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Activation of G-proteins induces Ca2+ oscillations with hyperpolarizing K+ currents in pancreatic beta-cells.
- 1991
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Ingår i: Second messengers and phosphoproteins. - 0895-7479. ; 14:3, s. 173-83
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Tidskriftsartikel (refereegranskat)abstract
- Activation of G-proteins by internal perfusion with GTP-gamma-S or external application of carbachol resulted in oscillations of cytoplasmic Ca2+ in isolated mouse pancreatic beta-cells. The Ca2+ transients were associated with the generation of K+ currents sufficiently pronounced to induce marked pulses of hyperpolarization. The oscillatory G-protein response remained largely unaffected when altering the membrane potential. The oscillations became less frequent in the presence of 1 mM neomycin and disappeared when the cells were internally perfused with 100 micrograms/ml heparin. The frequency of the oscillations was positively correlated with the basal level of cytoplasmic Ca2+. Addition of Ca2+ to the internal perfusion medium increased the oscillatory rate and buffering of the ion with Indo-1 or EGTA had the opposite effect. It is concluded that G-protein activation results in cyclic mobilisation of intracellular calcium mediated by inositol-1,4,5-triphosphate and that the basal concentration of cytoplasmic Ca2+ is an important determinant for the frequency of the oscillations.
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| 2. |
- Lund, P E, et al.
(författare)
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Intracellular ATP mimics GTP-gamma-S in generating Ca2+ oscillations in pancreatic beta-cells.
- 1991
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Ingår i: Biochemical and Biophysical Research Communications - BBRC. - 0006-291X .- 1090-2104. ; 177:2, s. 777-83
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Tidskriftsartikel (refereegranskat)abstract
- Intracellular free calcium ([Ca2+]i) was measured in individual pancreatic beta-cells from mice using dual emission microfluorometry and the indicator Indo-1 applied by a patch clamp pipette. GTP-gamma-S (100 microM) injected together with 0.3 or 3 mM ATP evoked repetitive [Ca2+]i transients with a frequency of about 1 per min in beta-cells kept at a membrane potential of -70 mV. The oscillatory pattern was unaffected by the Ca2+ channel blocker verapamil (50 microM). When omitting GTP-gamma-S from the pipette medium it became evident that 3 mM ATP alone can induce oscillations. The results provide additional evidence for an important role of ATP in the ionic control of insulin release, indicating that such regulation may also involve activation of G-proteins.
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| 3. |
- Lund, P E, et al.
(författare)
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Stimulation of insulin release by isosmolar addition of permeant molecules.
- 1992
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Ingår i: Molecular and Cellular Biochemistry. - 0300-8177 .- 1573-4919. ; 109:1, s. 77-81
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatic beta-cells are known to respond to hyposmolar stress by releasing insulin. It was evident from perifusion studies using islet cells from ob/ob-mice mixed with polyacrylamide beads that a similar type of secretory response can be obtained by isosmolar addition of 10-25 mM of the rapidly penetrating urea molecule. There was no effect with hyperosmolar addition of urea. The urea-induced insulin release differed from the ordinary stimulation of secretion in not disappearing but being more pronounced after previous heating to 45 degrees C or removal of extracellular Ca2+. Isosmolar urea was exceptional as an insulin secretagogue in being effective also in the presence of the alpha 2-adrenergic agonist clonidine or when lowering the temperature to 24 degrees C. Further support for the idea that isosmolar addition of rapidly penetrating molecules induces insulin release was obtained by testing non-metabolizable glucose analogues. Whereas 25 mM 3-O-methyl-D-glucose doubled the secretory rate within 4 min, the non-permeant L-glucose had only a slight initial action. When not compensating for the alterations of the medium osmolarity 3-O-methyl-D-glucose was without effect. Although expansion of beta-cells cannot explain the existence of a pronounced initial secretory response to D-glucose it may under certain conditions contribute to the stimulatory effects of the sugar.
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| 4. |
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