| 1. |
- Arkhammar, P., et al.
(författare)
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Protein kinase C modulates the insulin secretory process by maintaining a proper function of the beta-cell voltage-activated Ca2+ channels
- 1994
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Ingår i: Journal of Biological Chemistry. - : Baishideng Publishers. - 0021-9258 .- 1083-351X. ; 269:4, s. 2743-2749
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Tidskriftsartikel (refereegranskat)abstract
- In the present study an attempt was made to further elucidate the molecular mechanisms whereby protein kinase C (PKC) modulates the beta-cell stimulus-secretion coupling. Regulation of Ca2+ channel activity, [Ca2+]i, and insulin release were investigated in both normal pancreatic mouse beta-cells and in similar beta-cells deprived of PKC activity. [Ca2+]i was measured with the intracellular fluorescent Ca2+ indicator fura-2 and the Ca2+ channel activity was estimated by the whole cell configuration of the patch-clamp technique. To reveal the various isoenzymes of PKC present in the mouse beta-cell, proteins were separated by one-dimensional gel electrophoresis and Western blotting was performed. The production of inositol phosphates was measured by ion-exchange chromatography and insulin release was measured radioimmunologically. Acute stimulation with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate resulted in suppression of both the carbamylcholine-induced increase in [Ca2+]i and production of inositol 1,4,5-trisphosphate. Under these conditions the increase in [Ca2+]i in response to glucose was similar to that found in control cells. When beta-cells were deprived of PKC, by exposure to 200 nM 12-O-tetradecanoylphorbol-13-acetate for 24-48 h, there was an enhanced response to carbamylcholine. This response constituted increases in both the [Ca2+]i signal and production of inositol 1,4,5-trisphosphate. Interestingly, cells with down-regulated PKC activity responded more slowly to glucose stimulation, when comparing the initial increase in [Ca2+]i, than control cells. On the other hand, the maximal increase in [Ca2+]i was similar whether or not PKC was present. Moreover, PKC down-regulated cells exhibited a significant reduction of maximal whole cell Ca2+ currents, a finding that may explain the altered kinetics with regard to the [Ca2+]i increase in response to the sugar. Both the alpha and beta 1 forms of the PKC isoenzymes were present in the mouse beta-cell and were also subjected to PKC down-regulation. Hence, either of these isoenzymes or both may be involved in the modulation of phospholipase C and Ca2+ channel activity. Since insulin release under physiological conditions is critically dependent on Ca(2+)-influx through the voltage-gated L-type Ca2+ channels, the kinetics of hormone release was expected to demonstrate a similar delay as that of the [Ca2+]i increase. Although not as pronounced, such a delay was indeed also observed in the onset of insulin release. There was, however, no effect on the total amounts of hormone released. There was,h owever, no effect on thet otal amounts of hormone released. The present study con- firms that PKC has multiple roles and thereby interacta at different sites in the complex series of events consti- tuting the #?-cell signal-transduction pathway. It is sug- gested that PKC may be tonically active and effective in the maintenance of the phosphorylation state of the voltage-gated L-type Ca2+ channel, enabling an appro- priate function of this channel in the insulin secretory process.
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| 2. |
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| 3. |
- Alling, Christer, et al.
(författare)
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Evaluation of ethanol effects on PLC signal transduction pathways using cell lines of neuronal origin
- 1993
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Ingår i: Alcohol and alcoholism. Supplement. - 1358-6173. ; 2, s. 295-299
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Tidskriftsartikel (refereegranskat)abstract
- Human neuroblastoma cells SH-SY5Y and neuroblastoma-glioma cells NG 108-15 have been used as models for the elucidation of the effects of ethanol on receptor-mediated phospholipase C activity, c-fos mRNA expression and protein kinase C activity. Cells were exposed to ethanol (0-200 mM) for varying periods up to seven days. Agonist stimulated events were obtained in NG 108-15 cells with bradykinin and in SH-SY5Y cells with carbachol. Chronic ethanol exposure reduced the agonist-stimulated formation of inositol 1,4,5-trisphosphate in NG 108-15 cells and in SH-SY5Y cells. 100 mM ethanol for seven days increased the membrane bound and cytosolic forms of protein kinase C activity in SH-SY5Y cells. Carbachol (1 mM) induced a maximal c-fos mRNA response after 40 minutes in SH-SY5Y cells, an effect that could be mimicked through protein kinase C stimulation by phorbol esters.
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| 4. |
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| 5. |
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| 6. |
- Hutton, R, et al.
(författare)
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Photon spectroscopy following electron-capture for the collision systems 10 keV/q Kr(q+) + He (q=7,8,9)
- 1993
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Ingår i: Physica Scripta. - 0031-8949. ; 48:5, s. 569-572
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Tidskriftsartikel (refereegranskat)abstract
- Spectral studies following electron capture in slow ion-atom collisions are reported for the collision systems Kr(q+) + He (q = 7, 8, 9) at 10 keV/q. The work introduces part of the spectroscopy program which is beginning at the University of Uppsala ECR ion source facility. In particular a search was made for the 3d(10)4p2P-3d(9)4S(2)2D transitions in Cu-like Kr. This multiplet was found to give transitions with wavelengths 198.56, 194.65 and 190.97 angstrom for the 3/2-5/2, 3/2-3/2 and 1/2-3/2 components respectively.
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| 7. |
- J. Tranvik, Lars, et al.
(författare)
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In situ mineralization of chlorinated phenols by pelagic bacteria in lakes of differing humic content
- 1991
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Ingår i: Environmental Toxicology and Chemistry. - : Wiley. - 0730-7268 .- 1552-8618. ; 10:2, s. 195-200
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Tidskriftsartikel (refereegranskat)abstract
- The microbial mineralization of phenol and three chlorinated phenols (3,4-dichlorophenol, 2,4,5-trichlorophenol and pentachlorophenol) in the water column of 23 pristine, oligotrophic lakes of different humic content was investigated. During short-term (∼2 d) in situ incubations of water samples amended with 14C-labeled phenolic compounds, the fraction of the added pollutant mineralized to 14CO2 was positively correlated with water color (an estimate of humic content) and the total organic carbon concentration of the water. The rate of mineralization per bacterial cell was not correlated with humic content, due to increased bacterial abundance with increasing humic content. Hence, the higher mineralization rate in humic lakes than in clear-water lakes was probably a result of higher bacterial abundance rather than being an effect of bacterial cells having a higher potential for the degradation of such compounds.
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| 8. |
- Jörnsten, Kurt O., et al.
(författare)
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An entropy model with variable target
- 1990
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Ingår i: Environment and planning A. - : SAGE Publications. - 0308-518X .- 1472-3409. ; 22:4, s. 493-506
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Tidskriftsartikel (refereegranskat)abstract
- In this paper an entropy model with variable target is presented, in which target values are assumed to belong to a specified convex set, so that multiple base-year information and forecasts of future trends can be handled without prior aggregation of such information into one fixed target.Three solution methods for such a model are presented -- one cutting-plane and two search methods -- all of which utilize the fact that entropy models with fixed targets can be solved efficiently. Some comments on potential applications and reasonable target-set specifications are made and numerical examples are presented
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| 9. |
- Larsson, Christer, et al.
(författare)
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Mechanisms of muscarinic receptor-stimulated expression of c-fos in SH-SY5Y cells
- 1994
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Ingår i: European Journal of Pharmacology. - 1879-0712. ; 268:1, s. 19-28
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Tidskriftsartikel (refereegranskat)abstract
- In this study, the signal cascade transducing carbachol stimulation into c-fos expression in SH-SY5Y neuroblastoma cells was investigated. 1,2-Diacylglycerol formation and c-fos expression were mediated via stimulation of muscarinic M1 receptors and the first 5 min of receptor stimulation were critical for these events. Application of 1,2-dioctanoylglycerol induced c-fos expression and this, as well as carbachol-stimulated c-fos expression, was inhibited by protein kinase C inhibitors. Increasing the intracellular Ca2+ concentration had only small effects on c-fos expression. There was a dependency on extracellular Ca2+ for maximal c-fos expression and 1,2-diacylglycerol formation. The carbachol-stimulated c-fos expression was potentiated by application of the protein phosphatase inhibitor okadaic acid. These results demonstrate the importance of 1,2-diacylglycerol formation for muscarinic receptor-stimulated, protein kinase C-mediated c-fos expression in the SH-SY5Y cells and that this cascade is counteracted by an okadaic acid-sensitive protein phosphatase.
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| 10. |
- Larsson, Per, et al.
(författare)
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Contaminated sediment as a source of PCBs in a river system
- 1990
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Ingår i: Canadian Journal of Fisheries and Aquatic Sciences. - : Canadian Science Publishing. - 0706-652X .- 1205-7533. ; 47:4, s. 746-754
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Tidskriftsartikel (refereegranskat)abstract
- The transport of PCBs (Aroclor 1242) in a river system in southern Sweden was governed by outflow from sediment in a 26-ha contaminated lake. Experiments in the lake revealed that 14 g PCBs/d escaped from the sediment, while sedimentation was 3 g PCB/d. Volatilization of PCBs from the lake surface was 0.02 g/d, which was considerably higher than the atmospheric fallout . The majority of the sediment-desorbed compounds (80%) remained at the river mouth, 60 km downstream, and entered the Baltic Sea. Desorption increased the ratio of tetrachlorobiphenyls to pentachlorobiphenyls in the water. Transport across the water/air interface was higher for trichlorobiphenyls, while atmospheric deposition was dominated by penta- and hexachlorobiphenyls. Therefore, the sediment of the lake acted as a source of PCBs entering the river system as well as the atmosphere.
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