| 121. |
- Satin, L. S., et al.
(författare)
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"Take Me To Your Leader": An Electrophysiological Appraisal of the Role of Hub Cells in Pancreatic Islets
- 2020
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Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 69:5, s. 830-836
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Tidskriftsartikel (refereegranskat)abstract
- The coordinated electrical activity of beta-cells within the pancreatic islet drives oscillatory insulin secretion. A recent hypothesis postulates that specially equipped "hub" or "leader" cells within the beta-cell network drive islet oscillations and that electrically silencing or optically ablating these cells suppresses coordinated electrical activity (and thus insulin secretion) in the rest of the islet. In this Perspective, we discuss this hypothesis in relation to established principles of electrophysiological theory. We conclude that whereas electrical coupling between beta-cells is sufficient for the propagation of excitation across the islet, there is no obvious electrophysiological mechanism that explains how hyperpolarizing a hub cell results in widespread inhibition of islet electrical activity and disruption of their coordination. Thus, intraislet diffusible factors should perhaps be considered as an alternate mechanism.
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| 122. |
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| 123. |
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| 124. |
- Sinnegger-Brauns, MJ, et al.
(författare)
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Isoform-specific regulation of mood behavior and pancreatic beta cell and cardiovascular function by L-type Ca2+ channels
- 2004
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Ingår i: Journal of Clinical Investigation. - 0021-9738. ; 113:10, s. 1430-1439
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Tidskriftsartikel (refereegranskat)abstract
- Ca(v)1.2 and Ca(v)1.3 L-type Ca2+ channels (LTCCs) are believed to underlie Ca2+ currents in brain, pancreatic beta cells, and the cardiovascular system. In the CNS, neuronal LTCCs control excitation-transcription coupling and neuronal plasticity. However, the pharmacotherapeutic implications of CNS LTCC modulation are difficult to study because LTCC modulators cause card iovascular (activators and. blockers) and neurotoxic (activators) effects. We selectively eliminated high dihydropyridine (DHP) sensitivity from Ca(v)1.2 alpha1 subunits (Ca(v)1.2DHP(-/-)) without affecting function and expression. This allowed separation of the DHP effects of Ca(v)1.2 from those of Ca(v)1.3 and other LTCCs. DHP effects on pancreatic P cell LTCC currents, insulin secretion, cardiac inotropy, and arterial smooth muscle contractility were lost in Ca(v)1.2DHP(-/-) mice, which rules out a direct role of Ca(v)1.3 for these physiological processes. Using Ca(v)1.2DHP(-/-) mice, we established DHPs as mood-modifying agents: LTCC activator-induced neurotoxicity was abolished and disclosed a depression-like behavioral effect without affecting spontaneous locomotor activity. LTCC activator BayK 8644 (BayK) activated only a specific set of brain areas. In the ventral striatum, BayK-induced release of glutamate and 5-HT, but not dopamine and noradrenaline, was abolished. This animal model provides a useful tool to elucidate whether Ca(v)1.3-selective channel modulation represents a novel pharmacological approach to modify CNS function without major peripheral effects.
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| 125. |
- Soni, Arvind, et al.
(författare)
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GPRC5B a putative glutamate-receptor candidate is negative modulator of insulin secretion
- 2013
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Ingår i: Biochemical and Biophysical Research Communications. - : Elsevier BV. - 1090-2104 .- 0006-291X. ; 441:3, s. 643-648
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Tidskriftsartikel (refereegranskat)abstract
- GPRC5B is an orphan receptor belonging to the group C family of G protein-coupled receptors (GPCRs). GPRC5B is abundantly expressed in both human and mouse pancreatic islets, and both GPRC5B mRNA and protein are up-regulated 2.5-fold in islets from organ donors with type 2 diabetes. Expression of Gprc5b is 50% lower in islets isolated from newborn (<3 weeks) than in adult (>36 weeks) mice. Lentiviral shRNA-mediated down-regulation of Gprc5b in intact islets from 12 to 16 week-old mice strongly (2.5-fold) increased basal (I mmol/l) and moderately (40%) potentiated glucose (20 mmol/l) stimulated insulin secretion and also enhanced the potentiating effect of glutamate on insulin secretion. Downregulation of Gprc5b protected murine insulin-secreting clonal MIN6 cells against cytokine-induced apoptosis. We propose that increased expression of GPRC5B contributes to the reduced insulin secretion and beta-cell viability observed in type-2 diabetes. Thus, pharmacological targeting of GPRC5B might provide a novel means therapy for the treatment and prevention of type-2 diabetes. (C) 2013 Elsevier Inc. All rights reserved.
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| 126. |
- Speidel, Dina, et al.
(författare)
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CAPS1 and CAPS2 Regulate Stability and Recruitment of Insulin Granules in Mouse Pancreatic beta Cells.
- 2008
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131. ; 7:1, s. 57-67
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Tidskriftsartikel (refereegranskat)abstract
- CAPS1 and CAPS2 regulate dense-core vesicle release of transmitters and hormones in neuroendocrine cells, but their precise roles in the secretory process remain enigmatic. Here we show that CAPS2(-/-) and CAPS1(+/-);CAPS2(-/-) mice, despite having increased insulin sensitivity, are glucose intolerant and that this effect is attributable to a marked reduction of glucose-induced insulin secretion. This correlates with diminished Ca(2+)-dependent exocytosis, a reduction in the size of the morphologically docked pool, a decrease in the readily releasable pool of secretory vesicles, slowed granule priming, and suppression of second-phase (but not first-phase) insulin secretion. In beta cells of CAPS1(+/-);CAPS2(-/-) mice, the lowered insulin content and granule numbers were associated with an increase in lysosome numbers and lysosomal enzyme activity. We conclude that although CAPS proteins are not required for Ca(2+)-dependent exocytosis to proceed, they exert a modulatory effect on insulin granule priming, exocytosis, and stability.
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| 127. |
- Taneera, Jalal, et al.
(författare)
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Failure of Transplanted Bone Marrow Cells to Adopt a Pancreatic β-Cell Fate
- 2006
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Ingår i: Diabetes. - Alexandria, USA : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 55:2, s. 290-296
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies in normal mice have suggested that transplanted bone marrow cells can transdifferentiate into pancreatic beta-cells at relatively high efficiency. Herein, adopting the same and alternative approaches to deliver and fate map-transplanted bone marrow cells in the pancreas of normal as well as diabetic mice, we further investigated the potential of bone marrow transplantation as an alternative approach for beta-cell replacement. In contrast to previous studies, transplanted bone marrow cells expressing green fluorescence protein (GFP) under the control of the mouse insulin promoter failed to express GFP in the pancreas of normal as well as diabetic mice. Although bone marrow cells expressing GFP under the ubiquitously expressed beta-actin promoter efficiently engrafted the pancreas of normal and hyperglycemic mice, virtually all expressed CD45 and Mac-1/Gr-1, demonstrating that they adopt a hematopoietic rather than beta-cell fate, a finding further substantiated by the complete absence of GFP(+) cells expressing insulin and the beta-cell transcription factors pancreatic duodenal homeobox factor-1 and homeodomain protein. Thus, transplanted bone marrow cells demonstrated little, if any, capacity to adopt a beta-cell fate.
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| 128. |
- Tarasov, A. I., et al.
(författare)
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Dramatis Personae in β-Cell Mass Regulation: Enter SerpinB1
- 2016
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Ingår i: Cell Metabolism. - : Elsevier BV. - 1550-4131 .- 1932-7420. ; 23:1, s. 8-10
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Tidskriftsartikel (refereegranskat)abstract
- How is β-cell mass adjusted to changes in the functional insulin requirements? The answer to this question is central to the understanding of the causes and (potentially) the therapy of type 2 diabetes. In this issue of Cell Metabolism, El Ouaamari et al. (2016) report that increased production of the protease inhibitor SerpinB1 in the liver links insulin resistance to stimulation of β-cell proliferation. © 2016 Elsevier Inc.
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| 129. |
- Vikman, Jenny, et al.
(författare)
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Antibody inhibition of synaptosomal protein of 25 kDa (SNAP-25) and syntaxin 1 reduces rapid exocytosis in insulin-secreting cells.
- 2006
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Ingår i: Journal of Molecular Endocrinology. - : Bioscientifica. - 1479-6813 .- 0952-5041. ; 36:3, s. 503-515
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Tidskriftsartikel (refereegranskat)abstract
- SNARE-proteins (soluble NSF-attachment protein receptor) are important for Ca2+-dependent exocytosis. We have used capacitance measurements and confocal imaging to dissect the role of synaptosomal protein of 25 kDa (SNAP-25) and syntaxin 1 in rapid exocytosis in insulin-secreting pancreatic ß-cells. Following immunoneutralization of syntaxin 1 and SNAP-25, exocytosis was strongly reduced and associated with a marked reduction in the size of the readily releasable pool (RRP) by 65% and 86% in the presence of the anti-SNAP-25 and anti-syntaxin 1 antibodies respectively. The size of the immediately releasable pool (IRP), a subset of RRP in close association with the voltage-dependent Ca2+-channels, was reduced to an equal extent. The reduction in IRP correlated with slowed release kinetics and the time constant ({tau}) increased from a control value of 16 to 36 ms and 51 ms after inclusion of anti-SNAP-25 and anti-syntaxin 1 antibodies respectively in the pipette solution. We further show that SNAP-25 and syntaxin 1 aggregate in clusters along the plasma membrane. The size of these clusters was estimated to be ~300 nm and every ß-cell contained ~400 SNAP-25/syntaxin 1 clusters. Whereas the inhibitory action of the anti-syntaxin 1 antibody on exocytosis could be attributed almost entirely to suppression of the voltage-dependent Ca2+-current (–40%), the effect of the anti-SNAP-25 antibody was not mediated by decreased Ca2+-entry and is more likely due to a direct interference with the exocytotic machinery. Our data are consistent with the concept that both syntaxin 1 and SNAP-25 are required for rapid exocytosis in ß-cells.
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| 130. |
- Wendt, Anna, et al.
(författare)
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Glucose Inhibition of Glucagon Secretion From Rat alpha-Cells Is Mediated by GABA Released From Neighboring beta-Cells.
- 2004
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Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 53:4, s. 1038-1045
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Tidskriftsartikel (refereegranskat)abstract
- γ-Aminobutyric acid (GABA) has been proposed to function as a paracrine signaling molecule in islets of Langerhans. We have shown that rat β-cells release GABA by Ca2+-dependent exocytosis of synaptic-like microvesicles. Here we demonstrate that GABA thus released can diffuse over sufficient distances within the islet interstitium to activate GABAA receptors in neighboring cells. Confocal immunocytochemistry revealed the presence of GABAA receptors in glucagon-secreting α-cells but not in β- and δ-cells. RT-PCR analysis detected transcripts of α1 and α4 as well as β1–3 GABAA receptor subunits in purified α-cells but not in β-cells. In whole-cell voltage-clamp recordings, exogenous application of GABA activated Cl− currents in α-cells. The GABAA receptor antagonist SR95531 was used to investigate the effects of endogenous GABA (released from β-cells) on pancreatic islet hormone secretion. The antagonist increased glucagon secretion at 1 mmol/l glucose twofold and completely abolished the inhibitory action of 20 mmol/l glucose on glucagon release. Basal and glucose-stimulated secretion of insulin and somatostatin were unaffected by SR95531. The L-type Ca2+ channel blocker isradipine evoked a paradoxical stimulation of glucagon secretion. This effect was not observed in the presence of SR95531, and we therefore conclude that isradipine stimulates glucagon secretion by inhibition of GABA release.
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