| 1. |
- Arandia-Gorostidi, Nestor, et al.
(författare)
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Efficient carbon and nitrogen transfer from marine diatom aggregates to colonizing bacterial groups
- 2022
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 12:1
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Tidskriftsartikel (refereegranskat)abstract
- Bacterial degradation of sinking diatom aggregates is key for the availability of organic matter in the deep-ocean. Yet, little is known about the impact of aggregate colonization by different bacterial taxa on organic carbon and nutrient cycling within aggregates. Here, we tracked the carbon (C) and nitrogen (N) transfer from the diatom Leptocylindrus danicus to different environmental bacterial groups using a combination of C-13 and N-15 isotope incubation (incubated for 72 h), CARD-FISH and nanoSIMS single-cell analysis. Pseudoalteromonas bacterial group was the first colonizing diatom-aggregates, succeeded by the Alteromonas group. Within aggregates, diatom-attached bacteria were considerably more enriched in C-13 and N-15 than non-attached bacteria. Isotopic mass balance budget indicates that both groups showed comparable levels of diatom C in their biomass, accounting for 19 +/- 7% and 15 +/- 11%, respectively. In contrast to C, bacteria of the Alteromonas groups showed significantly higher levels of N derived from diatoms (77 +/- 28%) than Pseudoalteromonas (47 +/- 17%), suggesting a competitive advantage for Alteromonas in the N-limiting environments of the deep-sea. Our results imply that bacterial succession within diatom aggregates may largely impact taxa-specific C and N uptake, which may have important consequences for the quantity and quality of organic matter exported to the deep ocean.
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| 2. |
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| 3. |
- Helle, Frank, et al.
(författare)
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Angiotensin II-induced contraction is attenuated by nitric oxide in afferent arterioles from the nonclipped kidney in 2K1C
- 2009
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Ingår i: American Journal of Physiology - Renal Physiology. - : American Physiological Society. - 0363-6127 .- 1522-1466 .- 1931-857X. ; 296:1, s. F78-F86
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Tidskriftsartikel (refereegranskat)abstract
- Two-kidney, one-clip (2K1C) is a model of renovascular hypertension where we previously found an exaggerated intracellular calcium (Ca(i)(2+)) response to ANG II in isolated afferent arterioles (AAs) from the clipped kidney (Helle F, Vagnes OB, Iversen BM. Am J Physiol Renal Physiol 291: F140-F147, 2006). To test whether nitric oxide (NO) ameliorates the exaggerated ANG II response in 2K1C, we studied ANG II (10(-7) mol/l)-induced calcium signaling and contractility with or without the NO synthase (NOS) inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME). In AAs from the nonclipped kidney, l-NAME increased the ANG II-induced Ca(i)(2+) response from 0.28 +/- 0.05 to 0.55 +/- 0.09 (fura 2, 340 nm/380 nm ratio) and increased contraction from 80 +/- 6 to 60 +/- 6% of baseline (P < 0.05). In vessels from sham and clipped kidneys, l-NAME had no effect. In diaminofluorescein-FM diacetate-loaded AAs from the nonclipped kidney, ANG II increased NO-derived fluorescence to 145 +/- 34% of baseline (P < 0.05 vs. sham), but not in vessels from the sham or clipped kidney. Endothelial NOS (eNOS) mRNA and ser-1177 phosphorylation were unchanged in both kidneys from 2K1C, while eNOS protein was reduced in the clipped kidney compared with sham. Cationic amino acid transferase-1 and 2 mRNAs were increased in 2K1C, indicating increased availability of l-arginine for NO synthesis, but counteracted by decreased scavenging of the eNOS inhibitor asymmetric dimethylarginine by dimethylarginine dimethylaminohydrolase 2. In conclusion, the Ca(i)(2+) and contractile responses to ANG II are blunted by NO release in the nonclipped kidney. This may protect the nonclipped kidney from the hypertension and elevated ANG II levels in 2K1C.
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| 4. |
- Helle, Frank, et al.
(författare)
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Deletion of Notch3 Impairs Contractility of Renal Resistance Vessels Due to Deficient Ca2+ Entry
- 2022
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Ingår i: International Journal of Molecular Sciences. - : MDPI. - 1661-6596 .- 1422-0067. ; 23:24
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Tidskriftsartikel (refereegranskat)abstract
- Notch3 plays an important role in the differentiation and development of vascular smooth muscle cells. Mice lacking Notch3 show deficient renal autoregulation. The aim of the study was to investigate the mechanisms involved in the Notch3-mediated control of renal vascular response. To this end, renal resistance vessels (afferent arterioles) were isolated from Notch3(-/-) and wild-type littermates (WT) and stimulated with angiotensin II (ANG II). Contractions and intracellular Ca2+ concentrations were blunted in Notch3(-/-) vessels. ANG II responses in precapillary muscle arterioles were similar between the WT and Notch3(-/-) mice, suggesting a focal action of Notch3 in renal vasculature. Abolishing stored Ca2+ with thapsigargin reduced Ca2+ responses in the renal vessels of the two strains, signifying intact intracellular Ca2+ mobilization in Notch3(-/-). EGTA (Ca2+ chelating agent), nifedipine (L-type channel-blocker), or mibefradil (T-type channel-blocker) strongly reduced contraction and Ca2+ responses in WT mice but had no effect in Notch3(-/-) mice, indicating defective Ca2+ entry. Notch3(-/-) vessels responded normally to KCl-induced depolarization, which activates L-type channels directly. Differential transcriptomic analysis showed a major down-regulation of Cacna1h gene expression, coding for the alpha(1H) subunit of the T-type Ca2+ channel, in Notch3(-/-) vessels. In conclusion, renal resistance vessels from Notch3(-/-) mice display altered vascular reactivity to ANG II due to deficient Ca2+-entry. Consequently, Notch3 is essential for proper excitation-contraction coupling and vascular-tone regulation in the kidney.
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| 5. |
- Helle, Frank, et al.
(författare)
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Nitric oxide in afferent arterioles after uninephrectomy depends on extracellular L-arginine
- 2013
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Ingår i: AMERICAN JOURNAL OF PHYSIOLOGY-RENAL PHYSIOLOGY. - : American Physiological Society. - 1931-857X .- 1522-1466 .- 0363-6127. ; 304:8, s. F1088-F1098
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Tidskriftsartikel (refereegranskat)abstract
- Helle F, Skogstrand T, Schwartz IF, Schwartz D, Iversen BM, Palm F, Hultstrom M. Nitric oxide in afferent arterioles after uninephrectomy depends on extracellular L-arginine. Am J Physiol Renal Physiol 304: F1088-F1098, 2013. First published February 13, 2013; doi: 10.1152/ajprenal.00665.2011.-Uninephrectomy (UNX) causes hyperperfusion of the contralateral remaining kidney via increased nitric oxide (NO) synthesis. Although the exact mechanism remains largely unknown, we hypothesize that this would be localized to the afferent arteriole and that it depends on cellular uptake of L-arginine. The experiments were performed in rats 2 days (early) or 6 wk (late) after UNX and compared with controls (Sham) to study acute and chronic effects on NO metabolism. Renal blood flow was increased after UNX (21 +/- 2 ml.min(-1).kg(-1) in sham, 30 +/- 3 in early, and 26 +/- 1 in late, P andlt; 0.05). NO inhibition with N-omega-nitro-L-arginine methyl ester hydrochloride (L-NAME) caused a greater increase in renal vascular resistance in early UNX compared with Sham and late UNX (138 +/- 24 vs. 88 +/- 10, and 84 +/- 7%, P andlt; 0.01). The lower limit of autoregulation was increased both in early and late UNX compared with Sham (P andlt; 0.05). L-NAME did not affect the ANG II-induced contraction of isolated afferent arterioles (AA) from Sham. AA from early UNX displayed a more pronounced contraction in response to L-NAME (-57 +/- 7 vs. -16 +/- 7%, P andlt; 0.05) and in the absence of L-arginine (-41 +/- 4%, P andlt; 0.05) compared with both late UNX and Sham. mRNA expression of endothelial NO synthase was reduced, whereas protein expression was unchanged. Cationic amino acid transporter-1 and -2 mRNA was increased, while protein was unaffected in isolated preglomerular resistance vessels. In conclusion, NO-dependent hyperperfusion of the remaining kidney in early UNX is associated with increased NO release from the afferent arteriole, which is highly dependent on extracellular L-arginine availability.
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| 6. |
- Helle, Tina, et al.
(författare)
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Combining apps targeting professionals and senior citizens to improve housing accessibility and influence housing provision policies.
- 2015
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Ingår i: Studies in Health Technology and Informatics. - 0926-9630. - 9781614995654 ; 217, s. 300-305
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Konferensbidrag (refereegranskat)abstract
- Two separate apps that address the increasingly important issue of accessible housing for senior citizens have been developed in different project settings. One of the apps was developed to facilitate the process for professional raters to assess housing accessibility in the context of individual housing adaptations. The other app was developed for senior citizens to raise their awareness of possible accessibility problems in their current dwelling and in other apartments within the available housing stock. Both apps were developed with a high degree of active user involvement in processes utilizing multiple state of the art methods. The results are two well accepted prototype apps perceived as user-friendly and appropriate for the intended user groups. By combining these two apps, our ambition is for the professional raters to benefit by gaining knowledge of their clients' perceived needs and desires, and for senior citizens to benefit by getting access to a database of professionally rated dwellings. The ultimate goal is the generation of sound knowledge reflecting the needs and desires of senior citizens and professional requirements regarding accessible housing as a means to inform and influence housing provision policies.
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| 7. |
- Hultström, Michael, et al.
(författare)
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AT(1) receptor activation regulates the mRNA expression of CAT1, CAT2, arginase-1, and DDAH2 in preglomerular vessels from angiotensin II hypertensive rats.
- 2009
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Ingår i: American Journal of Physiology - Renal Physiology. - : American Physiological Society. - 0363-6127 .- 1522-1466 .- 1931-857X. ; 297:1, s. F163-8
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Tidskriftsartikel (refereegranskat)abstract
- Previously, we found increased expression of l-arginine metabolizing enzymes in both kidneys from two-kidney, one-clip (2K1C) hypertensive rats (Helle F, Hultstrom M, Skogstrand T, Palm F, Iversen BM. Am J Physiol Renal Physiol 296: F78-F86, 2009). In the present study, we investigate whether AT(1) receptor activation can induce the changes observed in 2K1C. Four groups of rats were infused with 80 ng/min ANG II or saline for 14 days and/or given 60 mg x kg(-1) x day(-1) losartan. Gene expression was studied in isolated preglomerular vessels by RT-PCR. Dose-responses to ANG II were studied in isolated preglomerular vessels with and without acute NOS inhibition [10(-4) mol/l N(G)-nitro-l-arginine methyl ester (l-NAME)]. Expressions of endothelial nitric oxide synthase (eNOS), caveolin-1, and arginase-2 were not changed by ANG II infusion. CAT1 (0.3 8 +/- 0.07 to 0.73 +/- 0.12, P < 0.05), CAT2 (1.14 +/- 0.29 to 2.74 +/- 0.48), DDAH2 (1.09 +/- 0.27 to 2.3 +/- 0.46), and arginase-1 (1.08 +/- 0.17 to 1.82 +/- 0.22) were increased in ANG II-infused rats. This was prevented by losartan treatment, which reduced the expression of eNOS (0.97 +/- 0.26 to 0.37 +/- 0.11 in controls; 0.8 +/- 0.16 to 0.36 +/- 0.1 in ANG II-infused rats) and caveolin-1 (2.49 +/- 0.59 to 0.82 +/- 0.24 in controls and 2.59 +/- 0.61 to 1.1 +/- 0.25 in ANG II-infused rats). ANG II (10(-10) mol/l) caused vessels from ANG II-infused animals to contract to 53 +/- 15% of baseline diameter and 90 +/- 5% of baseline diameter in controls (P < 0.05) and was further enhanced by l-NAME to 4 +/- 4% of baseline diameter (P < 0.05). In vivo losartan treatment reduced the reactivity of isolated vessels to 91 +/- 2% of baseline in response to 10(-7) mol/l ANG II compared with 82 +/- 3% in controls (P < 0.05) and prevented the increased responsiveness caused by ANG II infusion. In conclusion, CAT1, CAT2, DDAH2, and arginase-1 expression in renal resistance vessels is regulated through the AT(1) receptor. This finding may be of direct importance for NOS and the regulation of preglomerular vascular function.
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| 8. |
- Iversen, Bjarne M., et al.
(författare)
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Nitrogen oxyd (NO) og nyrearteriestenose
- 2008
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Ingår i: Nefrologisk forum. - : Norsk nyremedisinskforening. ; 14:2, s. 6-9
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Forskningsöversikt (övrigt vetenskapligt/konstnärligt)
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| 9. |
- Iversen, Morten Hvitfeldt, et al.
(författare)
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High resolution profiles of vertical particulate organic matter export off Cape Blanc, Mauritania : Degradation processes and ballasting effects
- 2010
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Ingår i: Deep Sea Research Part I. - : Elsevier BV. - 0967-0637 .- 1879-0119. ; 57:6, s. 771-784
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Tidskriftsartikel (refereegranskat)abstract
- Vertical carbon fluxes between the surface and 2500 m depth were estimated from in situ profiles of particle size distributions and abundances me/asured off Cape Blanc (Mauritania) related to deep ocean sediment traps. Vertical mass fluxes off Cape Blanc were significantly higher than recent global estimates in the open ocean. The aggregates off Cape Blanc contained high amounts of ballast material due to the presence of coccoliths and fine-grained dust from the Sahara desert, leading to a dominance of small and fast-settling aggregates. The largest changes in vertical fluxes were observed in the surface waters (<250 m), and, thus, showing this site to be the most important zone for aggregate formation and degradation. The degradation length scale (L), i.e. the fractional degradation of aggregates per meter settled, was estimated from vertical fluxes derived from the particle size distribution through the water column. This was compared with fractional remineralization rate of aggregates per meter settled derived from direct ship-board measurements of sinking velocity and small-scale 02 fluxes to aggregates measured by micro-sensors. Microbial respiration by attached bacteria alone could not explain the degradation of organic matter in the upper ocean. Instead, flux feeding from zooplankton organisms was indicated as the dominant degradation process of aggregated carbon in the surface ocean. Below the surface ocean, microbes became more important for the degradation as zooplankton was rare at these depths.
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| 10. |
- Iversen, M. H., et al.
(författare)
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Temperature effects on carbon-specific respiration rate and sinking velocity of diatom aggregates - potential implications for deep ocean export processes
- 2013
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 10:6, s. 4073-4085
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Tidskriftsartikel (refereegranskat)abstract
- Most deep ocean carbon flux profiles show low and almost constant fluxes of particulate organic carbon (POC) in the deep ocean. However, the reason for the non-changing POC fluxes at depths is unknown. This study presents direct measurements of formation, degradation, and sinking velocity of diatom aggregates from laboratory studies performed at 15 degrees C and 4 degrees C during a three-week experiment. The average carbon-specific respiration rate during the experiment was 0.12+/-0.03 at 15 degrees C, and decreased 3.5-fold when the temperature was lowered to 4 degrees C. No direct influence of temperature on aggregate sinking speed was observed. Using the remineralisation rate measured at 4 degrees C and an average particle sinking speed of 150 m d(-1), calculated carbon fluxes were similar to those collected in deep ocean sediment traps from a global data set, indicating that temperature plays a major role for deep ocean fluxes of POC.
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