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- Zhang, Quan
(författare)
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Cell coupling and exocytosis measured in intact mouse pancreatic islets Control of {delta}-cell secretion
- 2008
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Patch-clamp and capacitance measurements were applied to α-, β- and δ-cells in intact mouse pancreatic islets. The maximum rate of β-cell exocytosis during a depolarization to 0 mV was 14 granules/s, <5% of that observed in isolated β-cells. β-cell exocytosis exhibited bell-shaped voltage dependence and peaked at +20 mV. At physiological membrane potentials (≤-20 mV), the maximum rate of release was ~4 granules/s. Exocytosis in β-cell depends on Ca2+-influx via L-type Ca2+-channels, whereas N-type Ca2+-channels are important in α-cells. δ-cell exocytosis exhibits a post-stimulation component not observed in the other islet cell types. Ca2+-imaging in conjunction with capacitance measurements revealed that this feature results from Ca2+-induced Ca2+-release (CICR) via ryanodine receptor 3 (RyR3). Both somatostatin release measurements and patch-clamp experiments indicate that R-type Ca2+-channels are tightly coupled to CICR. The latency between Ca2+-influx through R-type Ca2+-channels and CICR was <6 ms. However, unlike what is observed in skeletal muscle, where association has been reported to be equally tight, Ca2+-influx is required in the δ-cells and no CICR can be evoked by depolarization alone. Glucose regulates CICR via promoting intracellular Ca2+ sequestration and cAMP/PKA-mediated modulation of RyR3. Electrophysiological analysis of cell coupling in intact islets reveals that every β-cell is electrically coupled to seven other β-cells. Coupling is sufficient to account for the synchronization and propagation of the cytosolic Ca2+-oscillations but small changes in β-cell electrical activity can be predicted to have strong effects on the synchronization which may contribute to the loss of pulsatile insulin secretion in type-2 diabetes.
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| 2. |
- Zhang, Quan, et al.
(författare)
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Cell coupling in mouse pancreatic beta-cells measured in intact islets of Langerhans
- 2008
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Ingår i: Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Science. - : The Royal Society. - 1364-503X .- 1471-2962. ; 366:1880, s. 3503-3523
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Tidskriftsartikel (refereegranskat)abstract
- The perforated whole-cell configuration of the patch-clamp technique was applied to functionally identified beta-cells in intact mouse pancreatic islets to study the extent of cell coupling between adjacent beta-cells. Using a combination of current- and voltage-clamp recordings, the total gap junctional conductance between beta-cells in an islet was estimated to be 1.22 nS. The analysis of the current waveforms in a voltage-clamped cell ( due to the. ring of an action potential in a neighbouring cell) suggested that the gap junctional conductance between a pair of beta-cells was 0.17 nS. Subthreshold voltage-clamp depolarization (to -55 mV) gave rise to a slow capacitive current indicative of coupling between beta-cells, but not in non-beta-cells, with a time constant of 13.5 ms and a total charge movement of 0.2 pC. Our data suggest that a superficial beta-cell in an islet is in electrical contact with six to seven other beta-cells. No evidence for dye coupling was obtained when cells were dialysed with Lucifer yellow even when electrical coupling was apparent. The correction of the measured resting conductance for the contribution of the gap junctional conductance indicated that the whole-cell K-ATP channel conductance (G(K,ATP)) falls from approximately 2.5 nS in the absence of glucose to 0.1 nS at 15 mM glucose with an estimated IC50 of approximately 4 mM. Theoretical considerations indicate that the coupling between beta-cells within the islet is sufficient to allow propagation of [Ca2+](i) waves to spread with a speed of approximately 80 mu m s(-1), similar to that observed experimentally in confocal [Ca2+](i) imaging.
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| 3. |
- Zhang, Quan, et al.
(författare)
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R-type Ca2+-channel-evoked CICR regulates glucose-induced somatostatin secretion
- 2007
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Ingår i: Nature Cell Biology. - : Springer Science and Business Media LLC. - 1465-7392 .- 1476-4679. ; 9:4, s. 171-453
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Tidskriftsartikel (refereegranskat)abstract
- Pancreatic islets have a central role in blood glucose homeostasis. In addition to insulin-producing beta-cells and glucagon-secreting alpha-cells, the islets contain somatostatin-releasing delta-cells(1). Somatostatin is a powerful inhibitor of insulin and glucagon secretion(2). It is normally secreted in response to glucose(3) and there is evidence suggesting its release becomes perturbed in diabetes(4). Little is known about the control of somatostatin release. Closure of ATP-regulated K+-channels (K-ATP-channels)(5) and a depolarization-evoked increase in cytoplasmic free Ca2+ concentration ([Ca2+](i))(6-8) have been proposed to be essential. Here, we report that somatostatin release evoked by high glucose (>= 10 mM) is unaffected by the K-ATP-channel activator diazoxide and proceeds normally in K-ATP-channel-deficient islets. Glucose-induced somatostatin secretion is instead primarily dependent on Ca2+-induced Ca2+-release (CICR). This constitutes a novel mechanism for K-ATP-channel-independent metabolic control of pancreatic hormone secretion.
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