| 61. |
- Hastoy, B., et al.
(författare)
-
Electrophysiological properties of human beta-cell lines EndoC-beta H1 and -beta H2 conform with human beta-cells
- 2018
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Ingår i: Scientific Reports. - : Springer Science and Business Media LLC. - 2045-2322. ; 8
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Tidskriftsartikel (refereegranskat)abstract
- Limited access to human islets has prompted the development of human beta cell models. The human beta cell lines EndoC-beta H1 and EndoC-beta H2 are increasingly used by the research community. However, little is known of their electrophysiological and secretory properties. Here, we monitored parameters that constitute the glucose-triggering pathway of insulin release. Both cell lines respond to glucose (6 and 20 mM) with 2- to 3-fold stimulation of insulin secretion which correlated with an elevation of [Ca2+](i), membrane depolarisation and increased action potential firing. Similar to human primary beta cells, K-ATP channel activity is low at 1mM glucose and is further reduced upon increasing glucose concentration; an effect that was mimicked by the K-ATP channel blocker tolbutamide. The upstroke of the action potentials reflects the activation of Ca2+ channels with some small contribution of TTX-sensitive Na+ channels. The repolarisation involves activation of voltage-gated Kv2.2 channels and large-conductance Ca2+-activated K+ channels. Exocytosis presented a similar kinetics to human primary beta cells. The ultrastructure of these cells shows insulin vesicles composed of an electrondense core surrounded by a thin clear halo. We conclude that the EndoC-beta H1 and -beta H2 cells share many features of primary human beta-cells and thus represent a useful experimental model.
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| 62. |
- Hastoy, B., et al.
(författare)
-
Fusion pore in exocytosis: More than an exit gate? A beta-cell perspective
- 2017
-
Ingår i: Cell Calcium. - : Elsevier BV. - 0143-4160. ; 68, s. 45-61
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Forskningsöversikt (refereegranskat)abstract
- Secretory vesicle exocytosis is a fundamental biological event and the process by which hormones (like insulin) are released into the blood. Considerable progress has been made in understanding this precisely orchestrated sequence of events from secretory vesicle docked at the cell membrane, hemifusion, to the opening of a membrane fusion pore. The exact biophysical and physiological regulation of these events implies a close interaction between membrane proteins and lipids in a confined space and constrained geometry to ensure appropriate delivery of cargo. We consider some of the still open questions such as the nature of the initiation of the fusion pore, the structure and the role of the Soluble N-ethylmaleimide-sensitive-factor Attachment protein REceptor (SNARE) transmembrane domains and their influence on the dynamics and regulation of exocytosis. We discuss how the membrane composition and protein-lipid interactions influence the likelihood of the nascent fusion pore forming. We relate these factors to the hypothesis that fusion pore expansion could be affected in type-2 diabetes via changes in disease-related gene transcription and alterations in the circulating lipid profile. Detailed characterisation of the dynamics of the fusion pore in vitro will contribute to understanding the larger issue of insulin secretory defects in diabetes.
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| 63. |
- Hatamie, Amir, et al.
(författare)
-
Nanoscale Amperometry Reveals that Only a Fraction of Vesicular Serotonin Content is Released During Exocytosis from Beta Cells
- 2021
-
Ingår i: Angewandte Chemie-International Edition. - : Wiley. - 1433-7851 .- 1521-3773. ; 60:14, s. 7593-7596
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Tidskriftsartikel (refereegranskat)abstract
- Recent work has shown that chemical release during the fundamental cellular process of exocytosis in model cell lines is not all-or-none. We tested this theory for vesicular release from single pancreatic beta cells. The vesicles in these cells release insulin, but also serotonin, which is detectible with amperometric methods. Traditionally, it is assumed that exocytosis in beta cells is all-or-none. Here, we use a multidisciplinary approach involving nanoscale amperometric chemical methods to explore the chemical nature of insulin exocytosis. We amperometrically quantified the number of serotonin molecules stored inside of individual nanoscale vesicles (39 317 +/- 1611) in the cell cytoplasm before exocytosis and the number of serotonin molecules released from single cells (13 310 +/- 1127) for each stimulated exocytosis event. Thus, beta cells release only one-third of their granule content, clearly supporting partial release in this system. We discuss these observations in the context of type-2 diabetes.
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| 64. |
- Haythorne, E., et al.
(författare)
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Diabetes causes marked inhibition of mitochondrial metabolism in pancreatic beta-cells
- 2019
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 10
-
Tidskriftsartikel (refereegranskat)abstract
- Diabetes is a global health problem caused primarily by the inability of pancreatic beta-cells to secrete adequate levels of insulin. The molecular mechanisms underlying the progressive failure of beta-cells to respond to glucose in type-2 diabetes remain unresolved. Using a combination of transcriptomics and proteomics, we find significant dysregulation of major metabolic pathways in islets of diabetic beta V59M mice, a non-obese, eulipidaemic diabetes model. Multiple genes/proteins involved in glycolysis/gluconeogenesis are upregulated, whereas those involved in oxidative phosphorylation are downregulated. In isolated islets, glucose-induced increases in NADH and ATP are impaired and both oxidative and glycolytic glucose metabolism are reduced. INS-1 beta-cells cultured chronically at high glucose show similar changes in protein expression and reduced glucose-stimulated oxygen consumption: targeted metabolomics reveals impaired metabolism. These data indicate hyperglycaemia induces metabolic changes in beta-cells that markedly reduce mitochondrial metabolism and ATP synthesis. We propose this underlies the progressive failure of beta-cells in diabetes.
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| 65. |
- Hoy, M, et al.
(författare)
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Imidazoline NNC77-0074 stimulates insulin secretion and inhibits glucagon release by control of Ca2+-dependent exocytosis in pancreatic alpha- and beta-cells
- 2003
-
Ingår i: European Journal of Pharmacology. - 1879-0712. ; 466:1-2, s. 213-221
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the effects of the novel imidazoline compound (+)-2-(2-(4,5-dihydro-1H-imidazol-2-yl)-thiopene-2-yl-ethyl)pyridine (NNC77-0074) on stimulus-secretion coupling in isolated pancreatic alpha- and beta-cells. NNC77-0074 stimulated glucose-dependent insulin secretion in intact mouse pancreatic islets. No effect was observed at less than or equal to 2.5 mM glucose and maximal stimulation occurred at 10-15 mM glucose. NNC77-0074 produced a concentration-dependent stimulation of insulin secretion. Half-maximal (EC50) stimulation was observed at 24 muM and at maximally stimulatory concentrations insulin release was doubled. The stimulatory action of NNC77-0074 on insulin secretion was not associated with membrane depolarisation or a change in the activity of ATP-sensitive K+ channels. Using capacitance measurements, we found that NNC77-0074 stimulated depolarisation-induced exocytosis 2.6-fold without affecting the whole-cell Ca2+ current when applied via the extracellular medium. The concentration dependence of the stimulatory action was determined by intracellular application of NNC77-0074 through the recording pipette. NNC77-0074 stimulated exocytosis half-maximal at 44 nM and at maximally stimulatory concentrations the rate of exocytosis was increased twofold. NNC77-0074 stimulated depolarised-induced insulin secretion from islets exposed to diazoxide and high external KCl (EC50 = 0.45 muM). The stimulatory action of NNC77-0074 was dependent on protein kinase C activity. NNC77-0074 potently inhibited glucagon secretion from rat islets (EC50 = I I nM). This was not associated with a change in spontaneous electrical activity and ATP-sensitive K channel activity but resulted from a reduction of the rate of Ca2+-dependent exocytosis in single rat alpha-cells (EC50=9 nM). Inhibition of exocytosis by NNC77-0074 was pertussis toxin-sensitive and mediated by activation of the protein phosphatase calcineurin. In rat somatotrophs, PC12 cells and mouse cortical neurons NNC77-0074 did not stimulate Ca2+-evoked exocytosis, whereas the other imidazoline compounds phentolamine and efaroxan produced 2.5-fold stimulation of exocytosis. Our data suggest that the imidazoline compound NNC77-0074 constitutes a novel class of antidiabetic compounds that stimulates glucose-dependent insulin release while inhibiting glucagon secretion. These actions are exclusively exerted by modulation of exocytosis of the insulin- and glucagon-containing granules. (C) 2003 Elsevier Science B.V. All rights reserved.
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| 66. |
- Hoy, M, et al.
(författare)
-
Tolbutamide stimulates exocytosis of glucagon by inhibition of a mitochondrial-like ATP-sensitive K+ (KATP) conductance in rat pancreatic A-cells
- 2000
-
Ingår i: Journal of Physiology. - 1469-7793 .- 0022-3751. ; 527:1, s. 109-120
-
Tidskriftsartikel (refereegranskat)abstract
- 1. Capacitance measurements were used to examine the effects of the sulphonylurea tolbutamide on Ca2+-dependent exocytosis in isolated glucagon-secreting rat pancreatic A-cells. 2. When applied extracellularly, tolbutamide stimulated depolarization-evoked exocytosis 4.2-fold without affecting the whole-cell Ca2+ current. The concentration dependence of the stimulatory action was determined by intracellular application through the recording pipette. Tolbutamide produced a concentration-dependent increase in cell capacitance. Half-maximal stimulation was observed at 33 microM and the maximum stimulation corresponded to a 3.4-fold enhancement of exocytosis. 3. The stimulatory action of tolbutamide was dependent on protein kinase C activity. The action of tolbutamide was mimicked by the general K+ channel blockers TEA (10 mM) and quinine (10 microM). A similar stimulation was elicited by 5-hydroxydecanoate (5-HD; 10 microM), an inhibitor of mitochondrial ATP-sensitive K+ (KATP) channels. 4. Tolbutamide-stimulated, but not TEA-induced, exocytosis was antagonized by the K+ channel openers diazoxide, pinacidil and cromakalim. 5. Dissipating the transgranular K+ gradient with nigericin and valinomycin inhibited tolbutamide- and Ca2+-evoked exocytosis. Furthermore, tolbutamide- and Ca2+-induced exocytosis were abolished by the H+ ionophore FCCP or by arresting the vacuolar (V-type) H+-ATPase with bafilomycin A1 or DCCD. Finally, ammonium chloride stimulated exocytosis to a similar extent to that obtained with tolbutamide. 6. We propose that during granular maturation, a granular V-type H+-ATPase pumps H+ into the secretory granule leading to the generation of a pH gradient across the granular membrane and the development of a positive voltage inside the granules. The pumping of H+ is facilitated by the concomitant exit of K+ through granular K+ channels with pharmacological properties similar to those of mitochondrial KATP channels. Release of granules that have been primed is then facilitated by the addition of K+ channel blockers. The resulting increase in membrane potential promotes exocytosis by unknown mechanisms, possibly involving granular alkalinization.
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| 67. |
- Immerstrand, Charlotte, 1974-
(författare)
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Biophysical studies of pigment transport in frog melanophores : impedance measurements and advanced microscopy analyses
- 2003
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Small proteins, other molecules and large organelles are frequently transported from one location to another within cells. These transports employ cytoskeletal networks and enable cells to maintain regions with different functions and attain an asymmetrical shape.The aim of this work was to explore biophysical methods for monitoring intracellular transport processes and associated structural changes. For these studies we have used pigment cells, melanophores, from the African clawed frog Xenopus laevis. In response to external stimuli, these cells can change colour by redistributing pigment granules in the cytoplasm.Transparent "cell clinics" equipped with gold electrodes were developed for impedance studies. The results show that impedance measurements at different frequencies not only can be used to monitor cell attachment and spreading, but also events like pigment aggregation. Significant F-actin breakdown and a cell area decrease may explain the impedance decrease seen during latrunculin-induced aggregation. In aggregation induced by melatonin there was, however, a small increase of the cell area, no F-actin breakdown and still lowered impedance, indicating that some other, likely intracellular mechanism is involved. In addition, confocal laser scanning microscopy (CLSM) studies showed that aggregation was associated with an increase in the cell height, more prominent for latrunculin than for melatonin. This height increase did not seem to involve influx of water through aquaporin channels at the cell membrane, or newly formed or remodelled microtubules in the cells.Besides impedance measurements, Image Correlation Spectroscopy (ICS) was applied to analyse pigment aggregation. The study shows for the first time that ICS can be used to analyse aggregation of non-fluorescent particles and suggests that the method may provide new information on the state of aggregation of granules in pigment cells.
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| 68. |
- Islam, M. Shahidul, et al.
(författare)
-
Ca(2+)-induced Ca2+ release in insulin-secreting cells
- 1992
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Ingår i: FEBS Letters. - : Wiley. - 0014-5793 .- 1873-3468. ; 296:3, s. 287-291
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Tidskriftsartikel (refereegranskat)abstract
- The sulphydryl reagent thimerosal (50 microM) released Ca2+ from a non-mitochondrial intracellular Ca2+ pool in a dose-dependent manner in permeabilized insulin-secreting RINm5F cells. This release was reversed after addition of the reducing agent dithiothreitol. Ca2+ was released from an Ins(1,4,5)P3-insensitive pool, since release was observed even after depletion of the Ins(1,4,5)P3-sensitive pool by a supramaximal dose of Ins(2,4,5)P3 or thapsigargin. The Ins(1,4,5)P3-sensitive pool remained essentially unaltered by thimerosal. Thimerosal-induced Ca2+ release was potentiated by caffeine. These findings suggest the existence of Ca(2+)-induced Ca2+ release also in insulin-secreting cells.
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| 69. |
- Islam, M. Shahidul, et al.
(författare)
-
Interaction with the inositol 1,4,5-trisphosphate receptor promotes Ca2+ sequestration in permeabilised insulin-secreting cells
- 1991
-
Ingår i: FEBS Letters. - 0014-5793 .- 1873-3468. ; 288:1-2, s. 27-29
-
Tidskriftsartikel (refereegranskat)abstract
- Electropermeabilised insulin-secreting RINm5F cells sequestered Ca2+, resulting in a steady-state level of the ambient free Ca2+ concentration corresponding to 723 +/- 127 nM (mean +/- SEM, n = 10), as monitored by a Ca(2+)-selective minielectrode. Inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) promoted a rapid and pronounced release of Ca2+. This Ca2+ was resequestered and a new steady-state Ca2+ level was attained, which was always lower (460 +/- 102 nM, n = 10, P less than 0.001) than the steady-state Ca2+ level maintained before the addition of Ins(1,4,5)P3. Whereas the initial reuptake of Ca2+ subsequent to Ins(1,4,5)P3 stimulation was relatively slow, the later part of reuptake was fast as compared to the reuptake phases of a pulse addition of extraneous Ca2+. In the latter case the uptake of Ca2+ resulted in a steady-state level similar to that found in the absence of Ins(1,4,5)P3. Addition of Ins(1,4,5)P3 under this condition resulted in a further Ca2+ uptake and thus a lower steady-state Ca2+ level. Heparin, which binds to the Ins(1,4,5)P3 receptor, also lowered the steady-state free Ca2+ concentration. In contrast to Ins(1,4,5)P3, inositol 1,3,4,5-tetrakisphosphate was without effect on Ca2+ sequestration. These findings are consistent with the presence of a high-affinity Ins(1,4,5)P3 receptor promoting continuous release of Ca2+ under basal conditions and/or the Ins(1,4,5)P3 receptor being actively involved in Ca2+ sequestration.
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| 70. |
- Jeans, Alexander F., et al.
(författare)
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A dominant mutation in Snap25 causes impaired vesicle trafficking, sensorimotor gating, and ataxia in the blind-drunk mouse
- 2007
-
Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 104:7, s. 2431-2436
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Tidskriftsartikel (refereegranskat)abstract
- The neuronal soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) complex is essential for synaptic vesicle exocytosis, but its study has been limited by the neonatal lethality of murine SNARE knockouts. Here, we describe a viable mouse line carrying a mutation in the b-isoform of neuronal SNARE synaptosomal-associated protein of 25 kDa (SNAP-25) The causative I67T missense mutation results in increased binding affinities within the SNARE complex, impaired exocytotic vesicle recycling and granule exocytosis in pancreatic beta-cells, and a reduction in the amplitude of evoked cortical excitatory postsynaptic potentials. The mice also display ataxia and impaired sensorimotor gating, a phenotype which has been associated with psychiatric disorders in humans. These studies therefore provide insights into the role of the SNARE complex in both diabetes and psychiatric disease.
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