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- Åberg, N David, 1970, et al.
(författare)
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Insulin-like growth factor-I increases astrocyte intercellular gap junctional communication and connexin43 expression in vitro.
- 2003
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Ingår i: Journal of neuroscience research. - : Wiley. - 0360-4012. ; 74:1, s. 12-22
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Tidskriftsartikel (refereegranskat)abstract
- Connexin43 (cx43) forms gap junctions in astrocytes, and these gap junctions mediate intercellular communication by providing transport of low-molecular-weight metabolites and ions. We have recently shown that systemic growth hormone increases cx43 in the brain. One possibility was that local brain insulin-like growth factor-I (IGF-I) could mediate the effect by acting directly on astrocytes. In the present study, we examined the effects of direct application of recombinant human IGF-I (rhIGF-I) on astrocytes in primary culture concerning cx43 protein expression and gap junctional communication (GJC). After 24 hr of stimulation with rhIGF-I under serum-free conditions, the GJC and cx43 protein were analyzed. Administration of 30 ng/ml rhIGF-I increased the GJC and the abundance of cx43 protein. Cell proliferation of the astrocytes was not significantly increased by rhIGF-I at this concentration. However, a higher concentration of rhIGF-I (150 ng/ml) had no effect on GJC/cx43 but increased cell proliferation. Because of the important modulatory role of IGF binding proteins (IGFBPs) on IGF-I action, we analyzed IGFBPs in conditioned media. In cultures with a low abundance of IGFBPs (especially IGFBP-2), the GJC response to 30 ng/ml rhIGF-I was 81%, compared with the average of 25%. Finally, as a control, insulin was given in equimolar concentrations. However, GJC was not affected, which suggests that rhIGF-I acted via IGF-I receptors. In summary, the data show that rhIGF-I may increase GJC/cx43, whereas a higher concentration of rhIGF-I--at which stimulation of proliferation occurred--did not affect GJC/cx43. Furthermore, IGFBP-2 appeared to modulate the action of rhIGF-I on GJC in astrocytes by a paracrine mechanism.
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| 2. |
- Carlsson, Fredrik, 1972-
(författare)
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Spectroscopic studies of irradiation induced defects in SiC
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Silicon carbide (SiC) with its applications has the potential to affect the everyday life of most citizens. As a material it has some outstanding properties concerning its mechanical and chemical toughness as well as its electrical properties for high power and high frequency applications. The main effect this will have on the society is large reductions of electrical energy losses in base stations for mobile communication, electrical power distribution, power adaptors for home electronics and several other applications. To realize this marvelous potential SiC has to move beyond its present state as an emerging semiconductor into a mature technology. On this path the processing of devices is one of the major steps, this includes ion-implantation where ions bombard the SiC to form regions with different electrical properties. The effect of ion-implantation and irradiation with other particles, which causes similar damage, have been studied and reported in the following seven papers. Paper I deals with a well-known defect labeled D1, which occurs after irradiation and subsequent high temperature annealing. We have found a correlation with an electrically measured defect HS 1 and the proposed pseudodonor model is confirmed for this defect. In paper II the same defect is studied but with a novel method named TraCE that combines the electrical and optical measurements and provides a direct correlation between the two techniques. Further effects of irradiation and the D1 defect are presented in paper III. The lifetime of carriers is one of the major parameters when producing devices for high power applications. The influence of irradiation dose and concentrations of the D1 defect on the carrier lifetime is reported. There is a second defect that occurs after high temperature annealing named DII" It requires implantation of ions to form unlike the DI where any kind irradiation causing lattice damage is sufficient. It has some very interesting properties, especially the high-energy local vibrational modes. These are unique to the Dn defect and are important for the validation of theoretical calculations. A detailed study of the properties of the Dn defect is presented in paper IV. SiC is a compound semiconductor with two sublattices consisting of silicon (Si) and carbon (C) in equal amounts. Depending on the orientation one sublattice will always be above and dose to the other. The direction of irradiation, a Si above C or vice versa, for electrons having an energy of 100-200keV will create different defects and their concentration will differ. The difference in defect introduction rates is presented in paper V and the effects it has on photoluminescence spectra is presented in paper VI. Since SiC is a very inert material, defects created usually requires temperatures from 500-2000°C to anneal and some defects do not disappear. In paper VII the defect reduction of the electrically measured HS2 defect and some of the alphabet lines measured by photoluminescence is observed. This occurs at room temperature with only the recombination energy of the induced electrons and holes unlike other cases where high temperatures are needed.
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