| 1. |
- Gusarova, Viktoria, et al.
(författare)
-
Genetic inactivation of ANGPTL4 improves glucose homeostasis and is associated with reduced risk of diabetes
- 2018
-
Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9, s. 1-11
-
Tidskriftsartikel (refereegranskat)abstract
- Angiopoietin-like 4 (ANGPTL4) is an endogenous inhibitor of lipoprotein lipase that modulates lipid levels, coronary atherosclerosis risk, and nutrient partitioning. We hypothesize that loss of ANGPTL4 function might improve glucose homeostasis and decrease risk of type 2 diabetes (T2D). We investigate protein-altering variants in ANGPTL4 among 58,124 participants in the DiscovEHR human genetics study, with follow-up studies in 82,766 T2D cases and 498,761 controls. Carriers of p.E40K, a variant that abolishes ANGPTL4 ability to inhibit lipoprotein lipase, have lower odds of T2D (odds ratio 0.89, 95% confidence interval 0.85-0.92, p = 6.3 × 10-10), lower fasting glucose, and greater insulin sensitivity. Predicted loss-of-function variants are associated with lower odds of T2D among 32,015 cases and 84,006 controls (odds ratio 0.71, 95% confidence interval 0.49-0.99, p = 0.041). Functional studies in Angptl4-deficient mice confirm improved insulin sensitivity and glucose homeostasis. In conclusion, genetic inactivation of ANGPTL4 is associated with improved glucose homeostasis and reduced risk of T2D.
|
|
| 2. |
- Dwivedi, Om Prakash, et al.
(författare)
-
Loss of ZnT8 function protects against diabetes by enhanced insulin secretion
- 2019
-
Ingår i: Nature Genetics. - : Springer Science and Business Media LLC. - 1061-4036 .- 1546-1718. ; , s. 1-22
-
Tidskriftsartikel (refereegranskat)abstract
- A rare loss-of-function allele p.Arg138* in SLC30A8 encoding the zinc transporter 8 (ZnT8), which is enriched in Western Finland, protects against type 2 diabetes (T2D). We recruited relatives of the identified carriers and showed that protection was associated with better insulin secretion due to enhanced glucose responsiveness and proinsulin conversion, particularly when compared with individuals matched for the genotype of a common T2D-risk allele in SLC30A8, p.Arg325. In genome-edited human induced pluripotent stem cell (iPSC)-derived β-like cells, we establish that the p.Arg138* allele results in reduced SLC30A8 expression due to haploinsufficiency. In human β cells, loss of SLC30A8 leads to increased glucose responsiveness and reduced KATP channel function similar to isolated islets from carriers of the T2D-protective allele p.Trp325. These data position ZnT8 as an appealing target for treatment aimed at maintaining insulin secretion capacity in T2D.
|
|
| 3. |
- Gromada, J, et al.
(författare)
-
Glucagon-like peptide I increases cytoplasmic calcium in insulin-secreting beta TC3-cells by enhancement of intracellular calcium mobilization
- 1995
-
Ingår i: Diabetes. - : American Diabetes Association. - 1939-327X .- 0012-1797. ; 44:7, s. 767-774
-
Tidskriftsartikel (refereegranskat)abstract
- In the insulin-secreting beta-cell line beta TC3, stimulation with 11.2 mmol/l glucose caused a rise in the intracellular free Ca2+ concentration ([Ca2+]i) in only 18% of the tested cells. The number of glucose-responsive cells increased after pretreatment of the cells with glucagon-like peptide I (GLP-I)(7-36)amide and at 10(-11) mol/l; 84% of the cells responded to glucose with a rise in [Ca2+]i. GLP-I(7-36)amide induces a rapid increase in [Ca2+]i only in cells exposed to elevated glucose concentrations (> or = 5.6 mmol/l). The action of GLP-I(7-36)amide and forskolin involved a 10-fold increase in cytoplasmic cAMP concentration and was mediated by activation of protein kinase A. It was not associated with an effect on the membrane potential but required some (small) initial entry of Ca2+ through voltage-dependent L-type Ca2+ channels, which then produced a further increase in [Ca2+]i by mobilization from intracellular stores. The latter effect reflected Ca(2+)-induced Ca2+ release and was blocked by ryanodine. Similar increases in [Ca2+]i were also observed in voltage-clamped cells, although there was neither activation of a background (Ca(2+)-permeable) inward current nor enhancement of the voltage-dependent L-type Ca2+ current. These observations are consistent with GLP-I(7-36) amide inducing glucose sensitivity by promoting mobilization of Ca2+ from intracellular stores. We propose that this novel action of GLP-I(7-36)amide represents an important factor contributing to its insulinotropic action.
|
|
| 4. |
|
|
| 5. |
- Hoy, M, et al.
(författare)
-
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
-
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.
|
|
| 6. |
|
|
| 7. |
|
|
| 8. |
|
|
| 9. |
|
|
| 10. |
- Salah, Heba, et al.
(författare)
-
Muscle-specific differences in expression and phosphorylation of the Janus kinase 2/Signal Transducer and Activator of Transcription 3 following long-term mechanical ventilation and immobilization in rats
- 2018
-
Ingår i: Acta Physiologica. - : WILEY. - 1748-1708 .- 1748-1716. ; 222:3
-
Tidskriftsartikel (refereegranskat)abstract
- Aim: Muscle wasting is one of the factors most strongly predicting mortality and morbidity in critically ill intensive care unit (ICU). This muscle wasting affects both limb and respiratory muscles, but the understanding of underlying mechanisms and muscle-specific differences remains incomplete. This study aimed at investigating the temporal expression and phosphorylation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway in muscle wasting associated with the ICU condition to characterize the JAK/STAT proteins and the related changes leading or responding to their activation during exposure to the ICU condition.Methods: A novel experimental ICU model allowing long-term exposure to the ICU condition, immobilization and mechanical ventilation, was used in this study. Rats were pharmacologically paralysed by post-synaptic neuromuscular blockade and mechanically ventilated for durations varying between 6hours and 14days to study muscle-specific differences in the temporal activation of the JAK/STAT pathway in plantaris, intercostal and diaphragm muscles.Results: The JAK2/STAT3 pathway was significantly activated irrespective of muscle, but muscle-specific differences were observed in the temporal activation pattern between plantaris, intercostal and diaphragm muscles.Conclusion: The JAK2/STAT3 pathway was differentially activated in plantaris, intercostal and diaphragm muscles in response to the ICU condition. Thus, JAK2/STAT3 inhibitors may provide an attractive pharmacological intervention strategy in immobilized ICU patients, but further experimental studies are required in the study of muscle-specific effects on muscle mass and function in response to both short- and long-term exposure to the ICU condition prior to the translation into clinical research and practice.
|
|
| 11. |
|
|
| 12. |
- Zhang, W, et al.
(författare)
-
Tomosyn is expressed in beta-cells and negatively regulates insulin exocytosis
- 2006
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 55:3, s. 574-581
-
Tidskriftsartikel (refereegranskat)abstract
- Tomosyn, a syntaxin-binding protein, is capable of dissociating mammalian homolog of the Caenorhabditis elegans unc-18 gene from syntaxin and is involved in the regulation of exocytosis. We have investigated the expression, cellular localization, and functional role of tomosyn in pancreatic β-cells. Western blotting revealed a 130-kDa protein corresponding to tomosyn in insulin-secreting β-cell lines. RT-PCR amplification showed that b-, m-, and s-tomosyn isoform mRNAs are expressed in β-cell lines and rat pancreatic islets. Immunohistochemistry revealed punctate tomosyn immunoreactivity in the cytoplasm of insulin-, glucagon-, pancreatic polypeptide–, and somatostatin-containing islet cells. Syntaxin 1 coimmunoprecipitated with tomosyn in extracts of insulin-secreting cells. Overexpression of m-tomosyn in mouse β-cells significantly decreased exocytosis, whereas inhibition of tomosyn expression by small interfering RNA increased exocytosis. Hence, in the pancreatic β-cell, tomosyn negatively regulates insulin exocytosis.
|
|
| 13. |
- Ahrén, Bo, et al.
(författare)
-
Incretin hormones and insulin secretion.
- 2004
-
Ingår i: Hormone and Metabolic Research. - : Georg Thieme Verlag KG. - 1439-4286 .- 0018-5043. ; 36:11-12, s. 733-734
-
Tidskriftsartikel (refereegranskat)
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
- Eliasson, Lena, et al.
(författare)
-
PKC-dependent stimulation of exocytosis by sulfonylureas in pancreatic beta cells
- 1996
-
Ingår i: Science. - : American Association for the Advancement of Science (AAAS). - 1095-9203 .- 0036-8075. ; 271:5250, s. 813-815
-
Tidskriftsartikel (refereegranskat)abstract
- Hypoglycemic sulfonylureas represent a group of clinically useful antidiabetic compounds that stimulate insulin secretion from pancreatic beta cells. The molecular mechanisms involved are not fully understood but are believed to involve inhibition of potassium channels sensitive to adenosine triphosphate (KATP channels) in the beta cell membrane, causing membrane depolarization, calcium influx, and activation of the secretory machinery. In addition to these effects, sulfonylureas also promoted exocytosis by direct interaction with the secretory machinery not involving closure of the plasma membrane KATP channels. This effect was dependent on protein kinase C (PKC) and was observed at therapeutic concentrations of sulfonylureas, which suggests that it contributes to their hypoglycemic action in diabetics.
|
|
| 18. |
- Gromada, J, et al.
(författare)
-
Adrenaline stimulates glucagon secretion in pancreatic A-cells by increasing the Ca2+ current and the number of granules close to the L-type Ca2+ channels.
- 1997
-
Ingår i: The Journal of General Physiology. - 0022-1295 .- 1540-7748. ; 110:3, s. 217-28
-
Tidskriftsartikel (refereegranskat)abstract
- We have monitored electrical activity, voltage-gated Ca2+ currents, and exocytosis in single rat glucagon-secreting pancreatic A-cells. The A-cells were electrically excitable and generated spontaneous Na+- and Ca2+-dependent action potentials. Under basal conditions, exocytosis was tightly linked to Ca2+ influx through omega-conotoxin-GVIA-sensitive (N-type) Ca2+ channels. Stimulation of the A-cells with adrenaline (via beta-adrenergic receptors) or forskolin produced a greater than fourfold PKA-dependent potentiation of depolarization-evoked exocytosis. This enhancement of exocytosis was due to a 50% enhancement of Ca2+ influx through L-type Ca2+ channels, an effect that accounted for <30% of the total stimulatory action. The remaining 70% of the stimulation was attributable to an acceleration of granule mobilization resulting in a fivefold increase in the number of readily releasable granules near the L-type Ca2+ channels.
|
|
| 19. |
- Gromada, J, et al.
(författare)
-
ATP-sensitive K+ channel-dependent regulation of glucagon release and electrical actiflty by glucose in wild-type and SUR1(-/-) mouse alpha-cells
- 2004
-
Ingår i: Diabetes. - 0012-1797. ; 53, s. 181-189
-
Konferensbidrag (refereegranskat)abstract
- Patch-clamp recordings and glucagon release measurements were combined to determine the role of plasma membrane ATP-sensitive K+ channels (K-ATP channels) in the control of glucagon secretion from mouse pancreatic alpha-cells. In wild-type mouse islets, glucose produced a concentration-dependent (half-maximal inhibitory concentration [IC50] = 2.5 mmol/l) reduction of glucagon release. Maximum inhibition (similar to50%) was attained at glucose concentrations >5 mmol/l. The sulfonylureas tolbutamide (100 mumol/l) and glibenclamide (100 nmol/l) inhibited glucagon secretion to the same extent as a maximally inhibitory concentration of glucose. In mice lacking functional KATP channels (SUR1(-/-)), glucagon secretion in the absence of glucose was lower than that observed in wild-type islets and both glucose (0-20 mmol/l) and the sulfonylureas failed to inhibit glucagon secretion. Membrane potential recordings revealed that a-cells generate action potentials in the absence of glucose. Addition of glucose depolarized the alpha-cell by similar to7 mV and reduced spike height by 30% Application of tolbutamide likewise depolarized the alpha-cell (similar to17 mV) and reduced action potential amplitude (43%). Whereas insulin secretion increased monotonically with increasing external K+ concentrations (threshold 25 mmol/l), glucagon secretion was paradoxically suppressed at intermediate concentrations (5.6-15 mmol/l), and stimulation was first detectable at > 25 mmol/l K+. In alpha-cells isolated from SUR1(-/-) mice, both tolbutamide and glucose failed to produce membrane depolarization. These effects correlated with the presence of a small (0.13 nS) sulfonylurea-sensitive conductance in wild-type but not in SUR1(-/-) a-cells. Recordings of the free cytoplasmic Ca2+ concentration ([Ca2+](i)) revealed that, whereas glucose lowered [Ca2+](i) to the same extent as application of tolbutamide, the Na+ channel blocker tetrodotoxin, or the Ca2+ channel blocker Co2+ in wild-type alpha-cells, the sugar was far less effective on [Ca2+](i) in SUR1(-/-) alpha-cells. We conclude that the K-ATP channel is involved in the control of glucagon secretion by regulating the membrane potential in the alpha-cell in a way reminiscent of that previously documented in insulin-releasing beta-cells. However, because alpha-cells possess a different complement of voltage-gated ion channels involved in action potential generation than the beta-cell, moderate membrane depolarization in alpha-cells is associated with reduced rather than increased electrical activity and secretion.
|
|
| 20. |
- Gromada, J, et al.
(författare)
-
ATP-sensitive K+ channel-dependent regulation of glucagon release and electrical activity by glucose in wild-type and SUR1-/- mouse alpha-cells
- 2004
-
Ingår i: Diabetes. - : American Diabetes Association. - 0012-1797 .- 1939-327X. ; 5353 Suppl 3, s. S181-S189
-
Tidskriftsartikel (refereegranskat)abstract
- Patch-clamp recordings and glucagon release measurements were combined to determine the role of plasma membrane ATP-sensitive K+ channels (KATP channels) in the control of glucagon secretion from mouse pancreatic α-cells. In wild-type mouse islets, glucose produced a concentration-dependent (half-maximal inhibitory concentration [IC50] = 2.5 mmol/l) reduction of glucagon release. Maximum inhibition (∼50%) was attained at glucose concentrations >5 mmol/l. The sulfonylureas tolbutamide (100 μmol/l) and glibenclamide (100 nmol/l) inhibited glucagon secretion to the same extent as a maximally inhibitory concentration of glucose. In mice lacking functional KATP channels (SUR1−/−), glucagon secretion in the absence of glucose was lower than that observed in wild-type islets and both glucose (0–20 mmol/l) and the sulfonylureas failed to inhibit glucagon secretion. Membrane potential recordings revealed that α-cells generate action potentials in the absence of glucose. Addition of glucose depolarized the α-cell by ∼7 mV and reduced spike height by 30% Application of tolbutamide likewise depolarized the α-cell (∼17 mV) and reduced action potential amplitude (43%). Whereas insulin secretion increased monotonically with increasing external K+ concentrations (threshold 25 mmol/l), glucagon secretion was paradoxically suppressed at intermediate concentrations (5.6–15 mmol/l), and stimulation was first detectable at >25 mmol/l K+. In α-cells isolated from SUR1−/− mice, both tolbutamide and glucose failed to produce membrane depolarization. These effects correlated with the presence of a small (0.13 nS) sulfonylurea-sensitive conductance in wild-type but not in SUR1−/− α-cells. Recordings of the free cytoplasmic Ca2+ concentration ([Ca2+]i) revealed that, whereas glucose lowered [Ca2+]i to the same extent as application of tolbutamide, the Na+ channel blocker tetrodotoxin, or the Ca2+ channel blocker Co2+ in wild-type α-cells, the sugar was far less effective on [Ca2+]i in SUR1−/− α-cells. We conclude that the KATP channel is involved in the control of glucagon secretion by regulating the membrane potential in the α-cell in a way reminiscent of that previously documented in insulin-releasing β-cells. However, because α-cells possess a different complement of voltage-gated ion channels involved in action potential generation than the β-cell, moderate membrane depolarization in α-cells is associated with reduced rather than increased electrical activity and secretion.
|
|
| 21. |
- Gromada, J, et al.
(författare)
-
Multisite regulation of insulin secretion by cAMP-increasing agonists : evidence that glucagon-like peptide 1 and glucagon act via distinct receptors.
- 1997
-
Ingår i: Pflügers Archiv. - 0031-6768 .- 1432-2013. ; 434:5, s. 515-24
-
Tidskriftsartikel (refereegranskat)abstract
- The mechanisms by which glucagon-like peptide 1(7-36)amide (GLP-1[7-36]amide) potentiates insulin secretion were investigated by measurements of whole-cell K+ and Ca2+ currents, membrane potential, the cytoplasmic Ca2+ concentration ([Ca2+]i) and exocytosis in mouse pancreatic B-cells. GLP-1(7-36)amide (10 nM) stimulated glucose-induced (10 mM) electrical activity in intact pancreatic islets. The effect was manifested as a 34% increase in the duration of the bursts of action potentials and a corresponding 28% shortening of the silent intervals. GLP-1(7-36)amide had no effect on the electrical activity at subthreshold glucose concentrations (< or = 6.5 mM). In cultured B-cells, GLP-1(7-36)amide produced a decrease of the whole-cell ATP-sensitive K+ (KATP) conductance remaining at 5 mM glucose by approximately 30%. This effect was associated with membrane depolarization and the initiation of electrical activity. GLP-1(7-36)amide produced a protein-kinase-A-(PKA-) and glucose-dependent fourfold potentiation of Ca(2+)-induced exocytosis whilst only increasing the Ca2+ current marginally. The stimulatory action of GLP-1(7-36)amide on exocytosis was mimicked by the pancreatic hormone glucagon and exendin-4, a GLP-1 receptor agonist. Whereas the stimulatory action of GLP-1(7-36)amide could be antagonized by exendin-(9-39), this peptide did not interfere with the ability of glucagon to stimulate exocytosis. We suggest that GLP-1(7-36)amide and glucagon stimulate insulin secretion by binding to distinct receptors. The GLP-1(7-36)amide-induced stimulation of electrical activity and Ca2+ influx can account for (maximally) a doubling of insulin secretion. The remainder of its stimulatory action results from a cAMP/PKA-dependent potentiation of Ca(2+)-dependent exocytosis exerted at a stage distal to the elevation of [Ca2+]i.
|
|
| 22. |
- Gromada, J, et al.
(författare)
-
Nateglinide, but not repaglinide, stimulates growth hormone release in rat pituitary cells by inhibition of K+ channels and stimulation of cyclic AMP-dependent exocytosis
- 2002
-
Ingår i: European Journal of Endocrinology. - : Oxford University Press (OUP). - 1479-683X .- 0804-4643. ; 147:1, s. 133-142
-
Tidskriftsartikel (refereegranskat)abstract
- Objective: GH causes insulin resistance, impairs glycemic control and increases the risk of vascular diabetic complications. Sulphonylureas stimulate GH secretion and this study was undertaken to investigate the possible stimulatory effect of repaglinide and nateglinide, two novel oral glucose regulators, on critical steps of the stimulus-secretion coupling in single rat somatotrophs. Methods: Patch-clamp techniques were used to record whole-cell ATP-sensitive K+ (K-ATP) and delayed outward K+ currents, membrane potential and Ca2+-dependent exocytosis. GH release was measured from perifused rat somatotrophs. Results: Both nateglinide and repaglinide dose-dependently suppressed K-ATP channel activity with half-maximal inhibition being observed at 413 nM and 13 nM respectively. Both compounds induced action potential firing in the somatotrophs irrespective of whether GH-releasing hormone was present or not. The stimulation of electrical activity by nateglinide, but not repaglinide, was associated with an increased mean duration of the action potentials. The latter effect correlated with a reduction of the delayed outward K+ current, which accounts for action potential repolarization. The latter effect had a K-d of 19 muM but was limited to 38% inhibition. When applied at concentrations similar to those required to block K-ATP channels, nateglinide in addition potentiated Ca2+-evoked exocytosis 3.3-fold (K-d = 3 muM) and stimulated GH release 4.5-fold. The latter effect was not shared by repaglinide. The stimulation of exocytosis by nateglinide was mimicked by cAMP and antagonized by the protein kinase A inhibitor Rp-cAMPS. Conclusion: Nateglinide stimulates GH release by inhibition of plasma membrane K+ channels, elevation of cytoplasmic cAMP levels and stimulation of Ca2+-dependent exocytosis. By contrast, the effect of repaglinide was confined to inhibition of the K-ATP channels.
|
|
| 23. |
- Göpel, Sven, et al.
(författare)
-
Regulation of glucagon release in mouse -cells by KATP channels and inactivation of TTX-sensitive Na+ channels
- 2000
-
Ingår i: Journal of Physiology. - 1469-7793 .- 0022-3751. ; 528:3, s. 509-520
-
Tidskriftsartikel (refereegranskat)abstract
- The perforated patch whole-cell configuration of the patch-clamp technique was applied to superficial glucagon-secreting alpha-cells in intact mouse pancreatic islets. alpha-cells were distinguished from the beta- and delta-cells by the presence of a large TTX-blockable Na+ current, a TEA-resistant transient K+ current sensitive to 4-AP (A-current) and the presence of two kinetically separable Ca2+ current components corresponding to low- (T-type) and high-threshold (L-type) Ca2+ channels. The T-type Ca2+, Na+ and A-currents were subject to steady-state voltage-dependent inactivation, which was half-maximal at -45, -47 and -68 mV, respectively. Pancreatic alpha-cells were equipped with tolbutamide-sensitive, ATP-regulated K+ (KATP) channels. Addition of tolbutamide (0.1 mM) evoked a brief period of electrical activity followed by a depolarisation to a plateau of -30 mV with no regenerative electrical activity. Glucagon secretion in the absence of glucose was strongly inhibited by TTX, nifedipine and tolbutamide. When diazoxide was added in the presence of 10 mM glucose, concentrations up to 2 microM stimulated glucagon secretion to the same extent as removal of glucose. We conclude that electrical activity and secretion in the alpha-cells is dependent on the generation of Na+-dependent action potentials. Glucagon secretion depends on low activity of KATP channels to keep the membrane potential sufficiently negative to prevent voltage-dependent inactivation of voltage-gated membrane currents. Glucose may inhibit glucagon release by depolarising the alpha-cell with resultant inactivation of the ion channels participating in action potential generation.
|
|
| 24. |
|
|
| 25. |
|
|
| 26. |
- 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.
|
|
| 27. |
|
|
| 28. |
|
|
| 29. |
|
|
| 30. |
- Olsen, HL, et al.
(författare)
-
Phosphatidylinositol 4-kinase serves as a metabolic sensor and regulates priming of secretory granules in pancreatic beta cells
- 2003
-
Ingår i: Proceedings of the National Academy of Sciences. - : Proceedings of the National Academy of Sciences. - 1091-6490 .- 0027-8424. ; 100:9, s. 5187-5192
-
Tidskriftsartikel (refereegranskat)abstract
- Insulin secretion is controlled by the beta cell's metabolic state, and the ability of the secretory granules to undergo exocytosis increases during glucose stimulation in a membrane potential-independent fashion. Here, we demonstrate that exocytosis of insulin-containing secretory granules depends on phosphatidylinositol 4-kinase (PI 4-kinase) activity and that inhibition of this enzyme suppresses glucose-stimulated insulin secretion. Intracellular application of phosphaticlylinositol 4-phosphate and phosphatidylinositol 4,5-bisphosphate [Pl(4,5)P-2] stimulated exocytosis by promoting the priming of secretory granules for release and increasing the number of granules residing in a readily releasable pool. Reducing the cytoplasmic ADP concentration in a way mimicking the effects of glucose stimulation activated PI 4-kinase and increased exocytosis whereas changes of the ATP concentration in the physiological range had little effect. The PI(4,5)P-2-binding protein Ca2+-dependent activator protein for secretion (CAPS) is present in beta cells, and neutralization of the protein abolished both Ca2+- and PI(4,5)P-2-induced exocytosis. We conclude that ADP-induced changes in PI 4-kinase activity, via generation of Pl(4,5)P-2, represents a metabolic sensor in the beta cell by virtue of its capacity to regulate the release competence of the secretory granules.
|
|
