| 1. |
- Elmi, Adrian, et al.
(författare)
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Modulation of islet ATP content by inhibition or stimulation of the Na(+)/K(+) pump
- 2001
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Ingår i: European Journal of Pharmacology. - : Elsevier. - 0014-2999 .- 1879-0712. ; 426:1-2, s. 139-143
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Tidskriftsartikel (refereegranskat)abstract
- High (30 mM) K(+), known to cause beta-cell membrane depolarisation, significantly decreased the islet total ATP content, supporting the view that beta-cell membrane depolarisation can activate the ATP-consuming Na(+)/K(+) pump. Ouabain (1 mM) did not change the islet ATP content after 5-15 min of incubation in the absence or presence of 3 mM glucose but reduced it after 30 min, and in the presence of 20 mM glucose, the reduction by ouabain occurred already after 15 min. Incubation of islets with ouabain for 60 min decreased the islet ATP content in the presence of 3, 10 or 20 mM glucose or 30 mM K(+). Also, the islet glucose oxidation rate was decreased by ouabain. When K(+) deficiency was used to inhibit the Na(+)/K(+) pump, no change in ATP content was observed irrespective of glucose concentration, although K(+) deficiency caused a slight inhibition of the glucose oxidation rate. Diazoxide reduced the islet glucose oxidation rate and increased the islet ATP content in the presence of 20 mM glucose. There may exist a feedback mechanism decreasing the flow of glucose metabolism in response to reduced ATP consumption by the Na(+)/K(+) pump.
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| 2. |
- Johansson, Åsa, 1981-
(författare)
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Properties of Endothelium and its Importance in Endogenous and Transplanted Islets of Langerhans
- 2009
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Transplantation of insulin producing cells is currently the only cure for type 1 diabetes. However, even though the Edmonton protocol markedly increased the success rate of pancreatic islet transplantation, the long term insulin independence is still very poor. An adequate engraftment is critical for islet graft survival and function. In the present thesis, isolated islet endothelial cells were found to have a low proliferatory and migratory capacity towards vascular endothelial growth factor (VEGF), but this could be reversed by using neutralizing antibodies to the angiostatic factors thrombospondin-1, endostatin or alpha1-antitrypsin. In the adult islet endothelial cell, VEGF may act as a permeability inducer more than an inducer of angiogenesis. p38 MAP kinase activity has been shown to serve as a switch between these properties of VEGF. Inhibition of p38 MAP kinase by daily injections of SB203580 in the early posttransplantation phase lead to a redistribution of the islet graft blood vessels from the stroma into the endocrine tissue and this was accompanied by a higher oxygen tension. Besides transports of oxygen and nutrients, beta-cells may require signals from the endothelial cells for their growth and differentiation. It was demonstrated that islet endothelial cells secrete factors, including laminin, that have positive effects on beta-cell insulin release and insulin content. Our results suggest that improved revascularization of transplanted islets may be achieved by either inhibition of angiostatic factors, or by blocking p38 MAPkinase activity, in the implanted tissue. Islet endothelial cells have a supportive paracrine role for beta-cells that might be hampered by the normally poor revascularization.
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| 3. |
- Larsson-Nyrén, Gerd, et al.
(författare)
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Isolated mouse pancreatic β-cells show cell-specific temporal response pattern
- 2002
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Ingår i: American Journal of Physiology - Cell Physiology. - : ?. - 0363-6143 .- 1522-1563. ; 282:6, s. C1199-C1204
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Tidskriftsartikel (refereegranskat)abstract
- The length of the silent lag time before elevation of the cytosolic free Ca2+ concentration ([Ca2+]i) differs between individual pancreatic beta-cells. One important question is whether these differences reflect a random phenomenon or whether the length of lag time is inherent in the individual beta-cell. We compared the lag times, initial dips, and initial peak heights for [Ca2+]i from two consecutive glucose stimulations (with either 10 or 20 mM glucose) in individual ob/ob mouse beta-cells with the fura 2 technique in a microfluorimetric system. There was a strong correlation between the lengths of the lag times in each beta-cell (10 mM glucose: r = 0.94, P < 0.001; 20 mM glucose: r = 0.96, P < 0.001) as well as between the initial dips in [Ca2+]i (10 mM glucose: r = 0.93, P < 0.001; 20 mM glucose: r = 0.79, P < 0.001) and between the initial peak heights (10 mM glucose: r = 0.51, P < 0.01; 20 mM glucose: r = 0.77, P < 0.001). These data provide evidence that the response pattern, including both the length of the lag time and the dynamics of the subsequent [Ca2+]i, is specific for the individual beta-cell.
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| 4. |
- Larsson-Nyrén, Gerd, et al.
(författare)
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Perchlorate stimulates insulin secretion by shifting the gating of L-type Ca2+ currents in mouse pancreatic B-cells towards negative potentials
- 2001
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Ingår i: Pflügers Archiv. - : Springer Science and Business Media LLC. - 0031-6768 .- 1432-2013. ; 441:5, s. 587-595
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Tidskriftsartikel (refereegranskat)abstract
- The effects of the chaotrophic anion perchlorate (ClO4-) on glucose-induced electrical activity, exocytosis and ion channel activity in mouse pancreatic B-cells were investigated by patch-clamp recordings and capacitance measurements. ClO4- stimulated glucose-induced electrical activity and increased the action potential frequency by 70% whilst not affecting the membrane potential when applied in the presence of a subthreshold concentration of the sugar. ClO4- did not influence ATP-dependent K (KATP) channel activity and voltage-gated delayed K+ current. Similarly, ClO4- had no effect on Ca2+-dependent exocytosis. The stimulation of electrical activity and insulin secretion was instead attributable to an enhancement of the whole-cell Ca2+ current. This effect was particularly pronounced at voltages around the threshold for action potential initiation and a doubling of the current amplitude was observed at -30 mV. This was due to a 7-mV shift in the gating of the Ca2+ current towards negative voltages. The action of ClO4- was more pronounced when added in the presence of 0.1 mM BAY K8644, whereas no stimulation was observed when applied at a maximal concentration of the agonist (1 mM). Single-channel recordings revealed that the effect of ClO4- on whole-cell currents was principally due to a 60% increase in the mean duration of the long openings and the number of active channels. We propose that ClO4- stimulates insulin secretion and electrical activity by exerting a BAY K8644-like action on Ca2+ channel gating.
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| 5. |
- Nybom, Pia
(författare)
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On the Regulation of the Epithelial Paracellular Permeability
- 1996
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The epithelia of for instance the small intestine(s) plays a crucial role in the vectorial transport of nutrients and other solutes from the lumen to underlying body fluids, i.e. blood and lymph. However, the epithelial cells are also important in the formation and maintenance of a barrier towards harmful food components and toxic bacterial products. The research presented in this thesis aimed at further understanding theregulation of the paracellular permeability barrier in epithelia, especially in relation to structural modifications of the epithelial actin cytoskeleton and to intracellular signals. In particular, the objectives of the study were to: i) assess the associationbetween tight junctional integrity and the cytoskeleton by using cytochalasin B and dihydrocytochalasin B as modifying agents, ii) examine the involvement of phospho-inositide turnover in modulation of the paracellular barrier and the organization of the actin cytoskeleton, iii) investigate the participation of protein kinase C in the regulation of tight junctional integrity, iv) elucidate changes in the tight junction function andstructure caused by enterotoxigenic Vibrio cholerae, and v) examine the role of nitric oxide in the formation and regulation of the permeability barrier. To summarize, cytochalasin B and dihydrocytochalasin B mediate specific and dose-dependent effects on the transepithelial electrical resistance of MDCK-I epithelial cells. Furthermore, these alterations correlate well with distinct changes in the organization of filamentous actin and the tight junction-associated protein, Z0-1. Moreover, the actin-associated modulation of the epithelial barrier function appears to be dependent on phosphoinositide (PI) turnover, as elucidated by the combined effects of the PI 3-k:inase inhibitor, wortmannin, and dihydrocytochalasin B. The activation of protein kinase C with phorbol ester causes distinct changes in the transepithelial resistance and tight junction structure of MDCK-I and HT-29 cells. In addition, tight junctional function and structure also seem to be modulated by nitric oxide. A "new toxin", the hemagglutinin/protease (HNprotease) of Vibrio cho!erae was identified in the growth medium of a toxin-attenuated strain. The HA/protease causes characteristic alterations of the epithelial structure and barrier function, which were reduced in the presence of nitric oxide.
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| 6. |
- Ravier, M A, et al.
(författare)
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Disorganization of cytoplasmic Ca(2+) oscillations and pulsatile insulin secretion in islets from ob/ obmice
- 2002
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Ingår i: Diabetologia. - : Springer-Verlag New York. - 0012-186X .- 1432-0428. ; 45:8, s. 1154-1163
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Tidskriftsartikel (refereegranskat)abstract
- AIMS/HYPOTHESIS: In normal mouse islets, glucose induces synchronous cytoplasmic [Ca(2+)](i) oscillations in beta cells and pulses of insulin secretion. We investigated whether this fine regulation of islet function is preserved in hyperglycaemic and hyperinsulinaemic ob/ obmice.METHODS: Intact islets from ob/ ob mice and their lean littermates were used after overnight culture for measurement of [Ca(2+)](i) and insulin secretion.RESULTS: We observed three types of [Ca(2+)](i) responses during stimulation by 9 to 12 mmol/l of glucose: sustained increase, rapid oscillations and slow (or mixed) oscillations. They occurred in 8, 18 and 74% of lean islets and 9, 0 and 91% of ob/ ob islets, respectively. Subtle desynchronisation of [Ca(2+)](i) oscillations between regions occurred in 11% of lean islets. In ob/ ob islets, desynchronisation was frequent (66-82% depending on conditions) and prominent: oscillations were out of phase in different regions because of distinct periods and shapes. Only small ob/ ob islets were well synchronised, but sizes of synchronised lean and desynchronised ob/ ob islets were markedly overlapped. The occurrence of desynchronisation in clusters of 5 to 50 islet cells from ob/ obmice and not from lean mice further indicates that islet hypertrophy is not the only causal factor. In both types of islets, synchronous [Ca(2+)](i) oscillations were accompanied by oscillations of insulin secretion. In poorly synchronised ob/ ob islets, secretion was irregular but followed the pattern of the global [Ca(2+)](i) changes.CONCLUSIONS/INTERPRETATION: The regularity of glucose-induced [Ca(2+)](i) oscillations is disrupted in islets from ob/ ob mice and this desynchronisation perturbs the pulsatility of insulin secretion. A similar mechanism could contribute to the irregularity of insulin oscillations in Type II (non-insulin-dependent) diabetes mellitus.
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| 7. |
- Saiepour, Daniel, 1976-
(författare)
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Glucose and insulin modulate phagocytosis and production of reactive oxygen metabolites in human neutrophil granulocytes
- 2006
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Neutrophil granulocytes play an important role in the host defence against invading microorganisms and constitute the frontline of defence within the innate immune system and are among the first cells to arrive at the site of inflammation. Effective phagocytosis and killing of invading pathogens by neutrophils is of significant importance for successful resistance to infectious diseases. An important complication in diabetes mellitus is an increased sensitivity to infections and increased tissue damage, leading to many secondary diseases. This may in part be explained by an impaired function of neutrophil granulocytes. Since the exact mechanisms underlying defective neutrophil function in diabetes mellitus are not fully understood, the aim of the present study was to investigate the effects of elevated glucose and insulin concentrations on phagocytosis of opsonized yeast and on production of reactive oxygen metabolites (ROS) in normal human neutrophils. Elevated D-glucose concentrations (15-25 mM) inhibited the phagocytosis of C3bi- or IgG-opsonized yeast particles, which was neither an osmotic effect nor an effect due to reduced binding of opsonized yeast particles to the neutrophils. Inhibition of protein kinase C (PKC) by GF109203X or Go6976 could completely reverse the inhibitory effect of 25 mM D-glucose on phagocytosis. Diacylglycerol (DAG) dose-dependently inhibited phagocytosis and suboptimal inhibitory concentrations of DAG and glucose showed an additive inhibitory effect. Elevated concentrations of insulin (80-160 μU/ml) also inhibited neutrophil phagocytosis, an effect shown in part to be due to a delayed phagocytosis process. Insulin was found to increase the accumulation of cortical F-actin, without affecting the total cellular F-actin content. The PKCalpha/beta inhibitor, Go6976, abolished the insulin-mediated increase in cortical F-actin content and both Go6976 and the PKCalpha/beta/delta/epsilon-specific inhibitor GF109203X reversed the inhibitory effects of insulin on phagocytosis. The inhibition of phagocytosis by either glucose or insulin resulted in an expected reduction of intracellular respiratory burst. However, the extracellular release of ROS during phagocytosis was increased by insulin, but inhibited by glucose. The ability of insulin to enhance ROS production was found to be F-actin dependent. Data suggests that glucose inhibited intracellular respiratory burst activation by interfering with intracellular signaling downstream of PKC activation, whereas extracellular release of ROS was inhibited by glucose upstream of PKC signaling. Taken together these results suggest that both hyperglycemia and hyperinsulinemia inhibit complement receptor and Fc receptor-mediated phagocytosis in human neutrophils. Insulin, but not glucose, also induced an enhanced extracellular release of ROS during phagocytosis. The combination of reduced phagocytosis and alterations in ROS production may possibly explain both the increased sensitivity to infections and tissue damage seen in type 2 diabetes.
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| 8. |
- Saiepour, Daniel, et al.
(författare)
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Hyperglycemia-induced protein kinase C (PKC) activation inhibits phagocytosis of C3b- and IgG-opsonized yeast particles in normal human neutrophils
- 2003
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Ingår i: Experimental Diabesity Research. - 1543-8600 .- 1543-8619. ; 4:2, s. 125-132
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Tidskriftsartikel (refereegranskat)abstract
- The aim of this study was to investigate the effects of elevated glucose concentrations on complement receptor- and Fcgamma receptor-mediated phagocytosis in normal human neutrophils. D-Glucose at 15 or 25 mM dose-dependently inhibited both complement receptor- and Fcgamma receptor-mediated phagocytosis, as compared to that at a normal physiological glucose concentration. The protein kinase C (PKC) inhibitors GF109203X and Go6976 both dose-dependently and completely reversed the inhibitory effect of 25 mM D-glucose on phagocytosis. Complement receptor-mediated phagocytosis was dose-dependently inhibited by the cell permeable diacylglycerol analogue 1,2-dioctanoyl-sn-glycerol (DAG), an effect that was abolished by PKC inhibitors. Furthermore, suboptimal inhibitory concentrations of DAG and glucose showed an additive inhibitory effect on complement receptor-mediated phagocytosis. The authors conclude that elevated glucose concentrations can inhibit complement receptor and Fcgamma receptor-mediated phagocytosis in normal human neutrophils by activating PKCalpha and/or PKCbeta, an effect possibly mediated by DAG.
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| 9. |
- Saiepour, Daniel, et al.
(författare)
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Insulin inhibits phagocytosis in normal human neutrophils via PKCalpha/beta-dependent priming of F-actin assembly.
- 2006
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Ingår i: Inflammation Research. - : Springer Science and Business Media LLC. - 1023-3830 .- 1420-908X. ; 55:3, s. 85-91
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Tidskriftsartikel (refereegranskat)abstract
- OBJECTIVE: This study investigated the effects of insulin on the phagocytosis of C3bi - and IgG-opsonized yeast particles in normal human neutrophils. METHODS: Neutrophils were incubated in different insulin concentrations for 30 minutes and stimulated by C3bi - or IgG-opsonized yeast particles. Phagocytosis was quantified by both light microscopy and FACscan flow cytometry. Laser confocal microscopy was used for quantification of F-actin levels. RESULTS: Elevated insulin concentrations decreased neutrophil phagocytosis of both types of targets. This defect was shown to be in part due to a delayed phagocytosis in the presence of insulin. Following a 30 minute incubation, insulin was found to increase the accumulation of cortical F-actin, without affecting the total cellular F-actin content. The specific PKCalpha/beta inhibitor, Go6976, abolished the insulin-mediated increase in cortical F-actin content and both Go6976 and the PKCalpha/beta/delta/epsilon-specific inhibitor GF109203X reversed the inhibitory effects of insulin on phagocytosis. CONCLUSION: Hyperinsulinemia in vitro can inhibit phagocytosis of opsonized targets in normal human neutrophils. This effect of insulin is dependent on activation of PKCalpha and/or PKCbeta, and these insulin signals may interfere with the dynamic assembly/disassembly and/or distribution of F-actin, which is required for the phagocytosis process.
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| 10. |
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