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Al-Romaiyan A, Masocha W, Oyedemi S, Marafie SK, Huang GC, Jones PM, Persaud SJ. Commiphora myrrha stimulates insulin secretion from β-cells through activation of atypical protein kinase C and mitogen-activated protein kinase. JOURNAL OF ETHNOPHARMACOLOGY 2023; 302:115937. [PMID: 36410575 DOI: 10.1016/j.jep.2022.115937] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Revised: 08/22/2022] [Accepted: 11/11/2022] [Indexed: 06/16/2023]
Abstract
ETHNOPHARMACOLOGICAL RELEVANCE Ayurvedic medicine has been used in the treatment of diabetes mellitus for centuries. In Arabia and some areas of Africa, Commiphora myrrha (CM) has been extensively used as a plant-based remedy. We have previously shown that an aqueous CM resin solution directly stimulates insulin secretion from MIN6 cells, a mouse β-cell line, and isolated mouse and human islets. However, the signaling pathways involved in CM-induced insulin secretion are completely unknown. Insulin secretion is normally triggered by elevations in intracellular Ca2+ ([Ca2+]i) through voltage gated Ca2+ channels (VGCC) and activation of protein kinases. Protein and lipid kinases such as protein kinase A (PKA), Ca2+-calmodulin dependent protein kinase II (CaMKII), phosphoinositide 3-kinases (PI3Ks), protein kinase C (PKC) and mitogen-activated protein kinase (MAPK), specifically extracellular signal-regulated kinases (ERK1/2), may be involved in receptor-operated insulin secretion. Therefore, we hypothesized that CM may induce insulin secretion by modulating the activity of VGCC and/or one or more of the above kinases. AIM OF THE STUDY To investigate the possible molecular mechanism of action of CM-induced insulin secretion. The effects of aqueous CM resin extract on [Ca2+]i and protein kinase activation from β-cells were examined. METHODS The effect of aqueous CM resin solution on [Ca2+]i was assessed using Ca2+ microfluorimetry. The involvement of VGCC in CM-induced insulin secretion was investigated using static and perifusion insulin secretion experiments in the presence of either EGTA, a Ca2+ chelator, or nifedipine, a blocker of VGCC. The involvement of kinase activation in the stimulatory effect of CM on insulin secretion was examined by using static and perifusion insulin secretion experiments in the presence of known pharmacological inhibitors and/or downregulation of specific kinases. The effects of CM on phosphorylation of PKCζ and ERK1/2 were also assessed using the Wes™ capillary-based protein electrophoresis. RESULTS Ca2+ microfluorimetry measurements showed that exposing MIN6 cells to CM (0.5-2 mg/mL) was not associated with changes in [Ca2+]i. Similarly, incubating MIN6 cells and mouse islets with EGTA and nifedipine, respectively, did not attenuate the insulin secretion induced by CM. However, incubating mouse and human islets with CM in the presence of staurosporine, a non-selective protein kinase inhibitor, completely blocked the effect of CM on insulin secretion. Exposing mouse islets to CM in the presence of H89, KN62 and LY294002, inhibitors of PKA, CaMKII and PI3K, respectively, did not reduce CM-induced insulin secretion. However, incubating mouse and human islets with CM in the presence of Ro 31-8220, a pan-PKC inhibitor, diminished insulin secretion stimulated by CM, whereas inhibiting the action of typical PKC (with Go6976) and PLCβ (with U73122) did not affect CM-stimulated insulin secretion. Similarly, downregulating typical and novel PKC by chronic exposure of mouse islets to phorbol 12-myristate 13-acetate (PMA) was also not associated with a decrease in the stimulatory effect of CM on insulin secretion. Interestingly, CM-induced insulin secretion from mouse islets was inhibited in the presence of the PKCζ inhibitor ZIP and a MAPK inhibitor PD 98059. In addition, Wes™ capillary-based protein electrophoresis indicated that expression of the phosphorylated forms of PKCζ and ERK1/2, a MAPK, was significantly increased following exposure of INS-1832/13 cells, a rat insulinoma cell line, to CM. CONCLUSIONS Our data indicate that CM directly stimulates insulin secretion through activating known downstream effectors of insulin-stimulus secretion coupling. Indeed, the increase in insulin secretion seen with CM is independent of changes in [Ca2+]i and does not involve activation of VGCC. Instead, the CM stimulatory effect on insulin secretion is completely dependent on protein kinase activation. Our findings indicate that CM could induce insulin exocytosis by stimulating the phosphorylation and activation of PKCζ, which in turn phosphorylates and activates ERK1/2.
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Affiliation(s)
- Altaf Al-Romaiyan
- Department of Pharmacology & Therapeutics, Faculty of Pharmacy, Kuwait University, Kuwait.
| | - Willias Masocha
- Department of Pharmacology & Therapeutics, Faculty of Pharmacy, Kuwait University, Kuwait.
| | - Sunday Oyedemi
- School of Science and Technology, Nottingham Trent University, Clifton Lane, Nottingham, NG11 8NS, UK.
| | - Sulaiman K Marafie
- Biochemistry and Molecular Biology Department, Dasman Diabetes Institute, Kuwait.
| | - Guo-Cai Huang
- Department of Diabetes, School of Cardiovascular Medicine &Sciences, Faculty of Life Sciences and Medicine, King's College London, UK.
| | - Peter M Jones
- Department of Diabetes, School of Cardiovascular Medicine &Sciences, Faculty of Life Sciences and Medicine, King's College London, UK.
| | - Shanta J Persaud
- Department of Diabetes, School of Cardiovascular Medicine &Sciences, Faculty of Life Sciences and Medicine, King's College London, UK.
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Dirr EW, Urdaneta ME, Patel Y, Johnson RD, Campbell-Thompson M, Otto KJ. Designing a bioelectronic treatment for Type 1 diabetes: targeted parasympathetic modulation of insulin secretion. BIOELECTRONICS IN MEDICINE 2020; 3:17-31. [PMID: 33169091 PMCID: PMC7604671 DOI: 10.2217/bem-2020-0006] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2020] [Accepted: 06/29/2020] [Indexed: 12/31/2022]
Abstract
The pancreas is a visceral organ with exocrine functions for digestion and endocrine functions for maintenance of blood glucose homeostasis. In pancreatic diseases such as Type 1 diabetes, islets of the endocrine pancreas become dysfunctional and normal regulation of blood glucose concentration ceases. In healthy individuals, parasympathetic signaling to islets via the vagus nerve, triggers release of insulin from pancreatic β-cells and glucagon from α-cells. Using electrical stimulation to augment parasympathetic signaling may provide a way to control pancreatic endocrine functions and ultimately control blood glucose. Historical data suggest that cervical vagus nerve stimulation recruits many visceral organ systems. Simultaneous modulation of liver and digestive function along with pancreatic function provides differential signals that work to both raise and lower blood glucose. Targeted pancreatic vagus nerve stimulation may provide a solution to minimizing off-target effects through careful electrode placement just prior to pancreatic insertion.
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Affiliation(s)
- Elliott W Dirr
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA
| | - Morgan E Urdaneta
- Department of Neuroscience, University of Florida, Gainesville, FL 32611, USA
| | - Yogi Patel
- Department of Biomedical Engineering, Georgia Institute of Technology University of Florida, Gainesville, FL 32611, USA
| | - Richard D Johnson
- Department of Neuroscience, University of Florida, Gainesville, FL 32611, USA
- Department of Physiological Sciences, University of Florida, Gainesville, FL 32611, USA
| | - Martha Campbell-Thompson
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA
- Department of Pathology, Immunology, & Laboratory Medicine University of Florida, Gainesville, FL 32611, USA
| | - Kevin J Otto
- J. Crayton Pruitt Family Department of Biomedical Engineering, University of Florida, Gainesville, FL 32611, USA
- Department of Neuroscience, University of Florida, Gainesville, FL 32611, USA
- Department of Neurology, University of Florida, Gainesville, FL 32611, USA
- Department of Materials Science & Engineering, University of Florida, Gainesville, FL 32611, USA
- Department of Electrical & Computer Engineering, University of Florida, Gainesville, FL 32611, USA
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Sanchez‐Andres JV, Pomares R, Malaisse WJ. Adaptive short-term associative conditioning in the pancreatic β-cell. Physiol Rep 2020; 8:e14403. [PMID: 32232927 PMCID: PMC7105902 DOI: 10.14814/phy2.14403] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2019] [Revised: 02/19/2020] [Accepted: 02/20/2020] [Indexed: 01/21/2023] Open
Abstract
This study associates cholinergic stimulation of the pancreatic β-cell electrical activity with a short-term memory phenomenon. Glucose pulses applied to a basal glucose concentration induce depolarizing waves which are used to estimate the evolution of the β-cell glucose sensitivity. Exposure to carbamoylcholine (carbachol) increases the size of the glucose-induced depolarizing waves. This change appears after carbachol withdrawal and implies a temporal potentiation of sensitivity (TPS) lasting up to one hour. TPS induction requires the simultaneous action of carbachol and glucose. The substitution of glucose with the secretagogues glyceraldehyde or 2-ketoisocaproate mimics glucose-induced TPS, while palmitate does not. TPS is not produced if the membrane is kept hyperpolarized by diazoxide. Glucose can be replaced by tolbutamide, suggesting a role of depolarization and a subsequent increase in intracellular calcium concentration. A role for kinases is suggested because staurosporine prevents TPS induction. Cycloheximide does not impair TPS induction, indicating that de novo protein synthesis is not required. The fact that the two inputs acting simultaneously produce an effect that lasts up to one hour without requiring de novo protein synthesis suggests that TPS constitutes a case of short-term associative conditioning in non-neural tissue. The convergence of basal glucose levels and muscarinic activation happens physiologically during the cephalic phase of digestion, in order to later absorb incoming fuels. Our data reveals that the role of the cephalic phase may be extended, increasing nutrient sensitivity during meals while remaining low between them.
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Affiliation(s)
| | - Raquel Pomares
- Department of PhysiologyUniversidad Miguel HernandezAlicanteSpain
| | - Willy J. Malaisse
- Department of BiochemistryUniversité Libre de BruxellesBrusselsBelgium
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Niki I, Niwa T, Yu W, Budzko D, Miki T, Senda T. Ca2+Influx Does Not Trigger Glucose-Induced Traffic of the Insulin Granules and Alteration of Their Distribution. Exp Biol Med (Maywood) 2016; 228:1218-26. [PMID: 14610264 DOI: 10.1177/153537020322801019] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
This study investigated mechanisms by which glucose increases readily releasable secretory granules via acting on preexocytotic steps, i.e., intracellular granule movement and granule access to the plasma membrane using a pancreatic beta-cell line, MIN6. Glucose-induced activation of the movement occurred at a substimulatory concentration with regard to insulin output. Glucose activation of the movement was inhibited by pretreatment with thapsigargin plus acetylcholine to suppress intracellular Ca2+ mobilization. Inhibitors of calmodulin and myosin light chain kinase also suppressed glucose activation of the movement. Simultaneous addition of glucose with Ca2+ channel blockers or the ATP-sensitive K+ channel opener diazoxide failed to suppress the traffic activation, and addition of these substances on top of glucose stimulation resulted in a further increase. Although stimulatory glucose had minimal changes in the intracellular granule distribution, inhibition of Ca2+ influx revealed increases by glucose of the granules in the cell periphery. In contrast, high K+ depolarization decreased the peripheral granules. Glucose-induced granule margination was abolished when the protein kinase C activity was downregulated. These findings indicate that preexocytotic control of insulin release is regulated by distinct mechanisms from Ca2+ influx, which triggers insulin exocytosis. The nature of the regulation by glucose may explain a part of potentiating effects of the hexose independent of the closure of the ATP-sensitive K+ channel.
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Affiliation(s)
- Ichiro Niki
- Department of Pharmacology, Oita University, Faculty of Medicine, Oita 879-5593, Japan.
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Lee HJ, Choi YJ, Park SY, Kim JY, Won KC, Son JK, Kim YW. Hexane Extract of Orthosiphon stamineus Induces Insulin Expression and Prevents Glucotoxicity in INS-1 Cells. Diabetes Metab J 2015; 39:51-8. [PMID: 25729713 PMCID: PMC4342537 DOI: 10.4093/dmj.2015.39.1.51] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2014] [Accepted: 06/02/2014] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND Hyperglycemia, a characteristic feature of diabetes, induces glucotoxicity in pancreatic β-cells, resulting in further impairment of insulin secretion and worsening glycemic control. Thus, preservation of insulin secretory capacity is essential for the management of type 2 diabetes. In this study, we evaluated the ability of an Orthosiphon stamineus (OS) extract to prevent glucotoxicity in insulin-producing cells. METHODS We measured insulin mRNA expression and glucose-stimulated insulin secretion (GSIS) in OS-treated INS-1 cells after exposure to a high glucose (HG; 30 mM) concentration. RESULTS The hexane extract of OS elevated mRNA expression of insulin as well as pancreatic and duodenal homeobox-1 of INS-1 cells in a dose-dependent manner. The hexane OS extract also increased the levels of phosphorylated phosphatidylinositol 3-kinase (PI3K) in a concentration-dependent manner. Additionally, Akt phosphorylation was elevated by treatment with 100 and 200 µmol of the hexane OS extract. Three days of HG exposure suppressed insulin mRNA expression and GSIS; these expressions were restored by treatment with the hexane OS extract. HG elevated peroxide levels in the INS-1 cells. These levels were unaffected by OS treatment under both normal and hyperglycemic conditions. CONCLUSION Our results suggested that the hexane extract of OS elevates insulin mRNA expression and prevents glucotoxicity induced by a 3-day treatment with HG. This was associated with the activation of PI-3K and Akt.
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Affiliation(s)
- Hae-Jung Lee
- Department of Pediatrics, Samsung Changwon Hospital, Sungkyunkwan University School of Medicine, Changwon, Korea
| | - Yoon-Jung Choi
- Department of Physiology, Yeungnam University College of Medicine, Daegu, Korea
| | - So-Young Park
- Department of Physiology, Yeungnam University College of Medicine, Daegu, Korea
| | - Jong-Yeon Kim
- Department of Physiology, Yeungnam University College of Medicine, Daegu, Korea
| | - Kyu-Chang Won
- Department of Internal Medicine, Yeungnam University College of Medicine, Daegu, Korea
| | - Jong-Keun Son
- Yeungnam University College of Pharmacy, Gyeongsan, Korea
| | - Yong-Woon Kim
- Department of Physiology, Yeungnam University College of Medicine, Daegu, Korea
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Somesh BP, Verma MK, Sadasivuni MK, Mammen-Oommen A, Biswas S, Shilpa PC, Reddy AK, Yateesh AN, Pallavi PM, Nethra S, Smitha R, Neelima K, Narayanan U, Jagannath MR. Chronic glucolipotoxic conditions in pancreatic islets impair insulin secretion due to dysregulated calcium dynamics, glucose responsiveness and mitochondrial activity. BMC Cell Biol 2013; 14:31. [PMID: 23815372 PMCID: PMC3704974 DOI: 10.1186/1471-2121-14-31] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Accepted: 06/24/2013] [Indexed: 11/10/2022] Open
Abstract
Background In the progression towards diabetes, glucolipotoxicity is one of the main causes of pancreatic beta cell pathology. The aim of this study was to examine the in vitro effects of chronic glucolipotoxic conditions on cellular responses in pancreatic islets, including glucose and fat metabolism, Calcium mobilization, insulin secretion and insulin content. Results Exposure of islets to chronic glucolipotoxic conditions decreased glucose stimulated insulin secretion in vitro. Reduced protein levels of Glut2/slc2a2, and decreased glucokinase and pyruvate carboxylase mRNA levels indicated a significant lowering in glucose sensing. Concomitantly, both fatty acid uptake and triglyceride accumulation increased significantly while fatty acid oxidation decreased. This general suppression in glucose metabolism correlated well with a decrease in mitochondrial number and activity, reduction in cellular ATP content and dampening of the TCA cycle. Further, we also observed a decrease in IP3 levels and lower Calcium mobilization in response to glucose. Importantly, chronic glucolipotoxic conditions in vitro decreased insulin gene expression, insulin content, insulin granule docking (to the plasma membrane) and insulin secretion. Conclusions Our results present an integrated view of the effects of chronic glucolipotoxic conditions on known and novel signaling events, in vitro, that results in reduced glucose responsiveness and insulin secretion.
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Affiliation(s)
- Baggavalli P Somesh
- Connexios Life Sciences Pvt Ltd., No. 49, First Main road, 3rd phase, JP Nagar, Bangalore 560 078, India
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Angelini N, Rafacho A, Boschero AC, Bosqueiro JR. Involvement of the cholinergic pathway in glucocorticoid-induced hyperinsulinemia in rats. Diabetes Res Clin Pract 2010; 87:184-91. [PMID: 19962776 DOI: 10.1016/j.diabres.2009.11.008] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/13/2009] [Revised: 11/06/2009] [Accepted: 11/09/2009] [Indexed: 11/24/2022]
Abstract
AIMS We investigated the contribution of the cholinergic nervous system to dexamethasone-induced insulin resistance and hyperinsulinemia in rats. METHODS Seventy-day-old Wistar male rats were distributed in groups: control (CTL), vagotomized (VAG), and sham operated (SHAM). On the 90th day of life, half of the rats were treated daily with 1mg/kg of dexamethasone for 5 days (CTL DEX, VAG DEX, and SHAM DEX). RESULTS In the presence of 8.3mM glucose plus 100microM carbachol (Cch), isolated islets from CTL DEX secreted significantly more insulin than CTL. Cch-enhancement of secretion was further increased in islets from VAG CTL and VAG DEX than SHAM CTL and SHAM DEX, respectively. In CTL DEX islets, M3R and PLCbeta1 and phosphorylated PKCalpha, but not PKCalpha, protein content was significantly higher compared with each respective control. In islets from VAG DEX, the expression of M3R protein increased significantly compared to VAG CTL and SHAM DEX. Vagotomy per se did not affect insulin resistance, but attenuated fasted and fed insulinemia in VAG DEX, compared with SHAM DEX rats. CONCLUSION These data indicate an important participation of the cholinergic nervous system through muscaric receptors in dexamethasone-induced hyperinsulinemia in rats.
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Affiliation(s)
- Nágela Angelini
- Department of Anatomy, Cellular Biology and Physiology, Institute of Biology, State University of Campinas, São Paulo, Brazil
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8
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Baltrusch S, Lenzen S. Regulation of [Ca2+]i oscillations in mouse pancreatic islets by adrenergic agonists. Biochem Biophys Res Commun 2007; 363:1038-43. [DOI: 10.1016/j.bbrc.2007.09.028] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2007] [Accepted: 09/09/2007] [Indexed: 11/17/2022]
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Ferreira F, Filiputti E, Arantes VC, Stoppiglia LF, Araújo EP, Delghingaro-Augusto V, Latorraca MQ, Toyama MH, Boschero AC, Carneiro EM. Decreased cholinergic stimulation of insulin secretion by islets from rats fed a low protein diet is associated with reduced protein kinase calpha expression. J Nutr 2003; 133:695-9. [PMID: 12612139 DOI: 10.1093/jn/133.3.695] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
Undernutrition has been shown to affect the autonomic nervous system, leading to permanent alterations in insulin secretion. To understand these interactions better, we investigated the effects of carbamylcholine (CCh) and phorbol 12-myristate 13-acetate (PMA) on insulin secretion in pancreatic islets from rats fed a normal (17%; NP) or low (6%; LP) protein diet for 8 wk. Isolated islets were incubated for 1 h in Krebs-bicarbonate solution containing 8.3 mmol glucose/L, with or without PMA (400 nmol/L) and CCh. Increasing concentrations of CCh (0.1-1000 micro mol/L) dose dependently increased insulin secretion by islets from both groups of rats. However, insulin secretion by islets from rats fed the NP diet was significantly higher than that of rats fed the LP diet, and the dose-response curve to CCh was shifted to the right in islets from rats fed LP with a 50% effective concentration (EC(50)) of 2.15 +/- 0.7 and 4.64 +/- 0.1 micro mol CCh/L in islets of rats fed NP and LP diets, respectively (P < 0.05). PMA-induced insulin secretion was higher in islets of rats fed NP compared with those fed LP. Western blotting revealed that the protein kinase (PK)Calpha and phospholipase (PL)Cbeta(1) contents of islets of rats fed LP were 30% lower than those of islets of rats fed NP (P < 0.05). In addition, PKCalpha mRNA expression was reduced by 50% in islets from rats fed LP. In conclusion, a reduced expression of PKCalpha and PLCbeta(1) may be involved in the decreased insulin secretion by islets from LP rats after stimulation with CCh and PMA.
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Affiliation(s)
- Fabiano Ferreira
- Departamento de Fisiologia e Biofísica, Instituto de Biologia, Universidade Estadual de Campinas (UNICAMP), SP, Brasil
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Roderigo-Milne H, Hauge-Evans AC, Persaud SJ, Jones PM. Differential expression of insulin genes 1 and 2 in MIN6 cells and pseudoislets. Biochem Biophys Res Commun 2002; 296:589-95. [PMID: 12176022 DOI: 10.1016/s0006-291x(02)00913-0] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
There is some evidence that the two rodent insulin genes are differentially regulated in mice, although there is no satisfactory consensus on the relative levels and patterns of expression for the two genes. Using the mouse insulinoma cell line MIN6, we have demonstrated by quantitative RT-PCR, differential patterns of expression for the two genes. In mouse islets and early passage MIN6 cells, expression of ins 1 and ins 2 were found to be approximately equal, but levels of ins 1 mRNA diminished rapidly with continued passage. Furthermore, the ins 1 gene was found to be up-regulated in response to glucose stimulation and as a result of increased cell-cell contact, but no effect on the ins 2 gene was observed. Since the MIN6 cell line is frequently used as a beta-cell model for gene expression studies, consideration should be given to both insulin genes.
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Affiliation(s)
- Helen Roderigo-Milne
- Centre for Endocrinology and Reproduction Research, GKT School of Biomedical Sciences, King's College London, Guy's Campus, London Bridge, London SE1 9RT, UK.
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11
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Gilon P, Henquin JC. Mechanisms and physiological significance of the cholinergic control of pancreatic beta-cell function. Endocr Rev 2001; 22:565-604. [PMID: 11588141 DOI: 10.1210/edrv.22.5.0440] [Citation(s) in RCA: 181] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Acetylcholine (ACh), the major parasympathetic neurotransmitter, is released by intrapancreatic nerve endings during the preabsorptive and absorptive phases of feeding. In beta-cells, ACh binds to muscarinic M(3) receptors and exerts complex effects, which culminate in an increase of glucose (nutrient)-induced insulin secretion. Activation of PLC generates diacylglycerol. Activation of PLA(2) produces arachidonic acid and lysophosphatidylcholine. These phospholipid-derived messengers, particularly diacylglycerol, activate PKC, thereby increasing the efficiency of free cytosolic Ca(2+) concentration ([Ca(2+)](c)) on exocytosis of insulin granules. IP3, also produced by PLC, causes a rapid elevation of [Ca(2+)](c) by mobilizing Ca(2+) from the endoplasmic reticulum; the resulting fall in Ca(2+) in the organelle produces a small capacitative Ca(2+) entry. ACh also depolarizes the plasma membrane of beta-cells by a Na(+)- dependent mechanism. When the plasma membrane is already depolarized by secretagogues such as glucose, this additional depolarization induces a sustained increase in [Ca(2+)](c). Surprisingly, ACh can also inhibit voltage-dependent Ca(2+) channels and stimulate Ca(2+) efflux when [Ca(2+)](c) is elevated. However, under physiological conditions, the net effect of ACh on [Ca(2+)](c) is always positive. The insulinotropic effect of ACh results from two mechanisms: one involves a rise in [Ca(2+)](c) and the other involves a marked, PKC-mediated increase in the efficiency of Ca(2+) on exocytosis. The paper also discusses the mechanisms explaining the glucose dependence of the effects of ACh on insulin release.
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Affiliation(s)
- P Gilon
- Unité d'Endocrinologie et Métabolisme, University of Louvain Faculty of Medicine, B-1200 Brussels, Belgium.
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Efanov AM, Zaitsev SV, Berggren PO, Mest HJ, Efendic S. Imidazoline RX871024 raises diacylglycerol levels in rat pancreatic islets. Biochem Biophys Res Commun 2001; 281:1070-3. [PMID: 11243843 DOI: 10.1006/bbrc.2001.4483] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Imidazoline compound RX871024 and carbamylcholine (CCh) stimulate insulin secretion in isolated rat pancreatic islets. Combination of CCh and RX871024 induces a synergetic effect on insulin secretion. RX871024 and CCh produce twofold increases in diacylglycerol (DAG) concentration. The combination of two compounds has an additive effect on DAG concentration. Effects of RX871024 on insulin secretion and DAG concentration are not dependent on the presence of D609, an inhibitor of phosphatidylcholine-specific phospholipase C. It is concluded that as in case with CCh the increase in DAG concentration induced by imidazoline RX871024 contributes to the insulinotropic activity of the compound.
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Affiliation(s)
- A M Efanov
- Karolinska Institutet, Rolf Luft Center for Diabetes Research, Department of Molecular Medicine, Karolinska Hospital, Stockholm, S-171 76, Sweden
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Gromada J, Høy M, Renström E, Bokvist K, Eliasson L, Göpel S, Rorsman P. CaM kinase II-dependent mobilization of secretory granules underlies acetylcholine-induced stimulation of exocytosis in mouse pancreatic B-cells. J Physiol 1999; 518 ( Pt 3):745-59. [PMID: 10420011 PMCID: PMC2269462 DOI: 10.1111/j.1469-7793.1999.0745p.x] [Citation(s) in RCA: 81] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022] Open
Abstract
1. Measurements of cell capacitance were used to investigate the mechanisms by which acetylcholine (ACh) stimulates Ca2+-induced exocytosis in single insulin-secreting mouse pancreatic B-cells. 2. ACh (250 microM) increased exocytotic responses elicited by voltage-clamp depolarizations 2.3-fold. This effect was mediated by activation of muscarinic receptors and dependent on elevation of the cytoplasmic Ca2+ concentration ([Ca2+]i) attributable to mobilization of Ca2+ from intracellular stores. The latter action involved interference with the buffering of [Ca2+]i and the time constant (tau) for the recovery of [Ca2+]i following a voltage-clamp depolarization increased 5-fold. As a result, Ca2+ was present at concentrations sufficient to promote the replenishment of the readily releasable pool of granules (RRP; > 0.2 microM) for much longer periods in the presence than in the absence of the agonist. 3. The effect of Ca2+ on exocytosis was mediated by activation of CaM kinase II, but not protein kinase C, and involved both an increased size of the RRP from 40 to 140 granules and a decrease in tau for the refilling of the RRP from 31 to 19 s. 4. Collectively, the effects of ACh on the RRP and tau result in a > 10-fold stimulation of the rate at which granules are supplied for release.
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Affiliation(s)
- J Gromada
- Department of Islet Cell Physiology, Islet Discovery Research, Novo Nordisk A/S, Novo Allé, DK-2880 Bagsvaerd, Denmark.
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Jones PM, Persaud SJ. Protein kinases, protein phosphorylation, and the regulation of insulin secretion from pancreatic beta-cells. Endocr Rev 1998; 19:429-61. [PMID: 9715374 DOI: 10.1210/edrv.19.4.0339] [Citation(s) in RCA: 56] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Affiliation(s)
- P M Jones
- Biomedical Sciences Division, King's College London, United Kingdom.
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Love JA, Richards NW, Owyang C, Dawson DC. Muscarinic modulation of voltage-dependent Ca2+ channels in insulin-secreting HIT-T15 cells. THE AMERICAN JOURNAL OF PHYSIOLOGY 1998; 274:G397-405. [PMID: 9486195 DOI: 10.1152/ajpgi.1998.274.2.g397] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Potentiation of insulin secretion from pancreatic beta-cells by acetylcholine requires ongoing cyclic electrical activity initiated by other depolarizing secretagogues. Patch-clamp recordings in glucose-free solutions were made from the clonal beta-cell line HIT-T15 to determine whether the muscarinic agonist bethanechol (BCh) modulated voltage-dependent Ca2+ channels independent of effects on membrane potential. Only high-threshold, dihydropyridine-sensitive (L-type) Ca2+ channels with a mean conductance of 26 pS were observed in cell-attached patches. BCh (100 microM) caused a two- to threefold increase in both fractional open time and mean current of single Ca2+ channels. These changes resulted from a 44% decrease in the longer of two apparent mean closed times and a 25% increase in the mean open time. Similar BCh-stimulated increases in macroscopic Ca2+ currents were recorded in whole cell, perforated-patch recordings. The role of protein kinase C (PKC) in the muscarinic activation of Ca2+ channels was tested using a variety of PKC activators and inhibitors. Acute application of either the active phorbol ester phorbol 12-myristate 13-acetate (PMA) or the membrane-permeable diacylglycerol analog 1,2-didecanoyl-rac-glycerol mimicked the effects of BCh, whereas an inactive phorbol (4 alpha) had no effect. Depletion of PKC activity by chronic exposure to PMA or acute application of the PKC inhibitor staurosporine greatly reduced or abolished muscarinic activation of Ca2+ channels. These results are consistent with muscarinic activation of L-type, voltage-dependent Ca2+ channels mediated in large part by PKC.
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Affiliation(s)
- J A Love
- Department of Pharmacology and Toxicology, University of Mississippi Medical Center, Jackson 39216, USA
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16
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Harris TE, Persaud SJ, Saermark T, Jones PM. A myristoylated pseudosubstrate peptide inhibitor of protein kinase C: effects on glucose- and carbachol-induced insulin secretion. Mol Cell Endocrinol 1996; 121:133-41. [PMID: 8892314 DOI: 10.1016/0303-7207(96)03858-0] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
We have used synthetic pseudosubstrate peptide inhibitors of protein kinase C (PKC) to re-examine the role of conventional isoforms of PKC in the insulin secretory response of intact rat islets of Langerhans to glucose and to the cholinergic agonist carbachol (CCh). One peptide was modified by N-terminal myristoylation (PKC-myr20-28) to allow its use in intact beta-cells. Maximal inhibition of PKC activity in vitro required 10-fold less of this peptide (PKC-myr20-28) than of its non-myristoylated analogue. The maximum inhibitory concentration of PKC-myr20-28 had little effect on islet protein kinase A or Ca2+/calmodulin kinase activities. PKC-myr20-28 (25-100 microM) caused a dose-dependent inhibition of phorbol myristate acetate (PMA)-induced insulin secretion from intact rat islets but non-myristoylated peptides had little effect on the secretory response to PMA. A concentration of PKC-myr20-28 (100 microM) which maximally inhibited PMA-induced insulin secretion, also inhibited the secretory response to CCh, but did not affect glucose-stimulated insulin secretion from intact islets. These results indicate that myristoylation of pseudosubstrate peptides increases their potency as inhibitors and that PKC-myr20-28 is a selective and cell-permeant inhibitor of PMA-sensitive isoforms of PKC. They also suggest that the activation of PMA-sensitive PKC isoforms mediates the stimulatory effects of CCh, but is not obligatory for glucose-induced insulin secretion from pancreatic beta-cells.
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Affiliation(s)
- T E Harris
- Biomedical Sciences Division, King's College London, Kensington, UK.
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17
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Babb EL, Tarpley J, Landt M, Easom RA. Muscarinic activation of Ca2+/calmodulin-dependent protein kinase II in pancreatic islets. Temporal dissociation of kinase activation and insulin secretion. Biochem J 1996; 317 ( Pt 1):167-72. [PMID: 8694759 PMCID: PMC1217458 DOI: 10.1042/bj3170167] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Abstract
We have demonstrated previously that glucose activates the multifunctional Ca2+/calmodulin-dependent protein kinase II (CaM kinase II) in isolated rat pancreatic islets in a manner consistent with a role of this enzyme in the regulation of insulin secretion [Wenham, Landt and Easom (1994) J. Biol. Chem. 269, 4947-4952]. In the current study, the muscarinic agonist, carbachol, has been shown to induce the conversion of CaM kinase II into a Ca(2+)-independent, autonomous form indicative of its activation. Maximal activation (2-fold) was achieved by 15 s, followed by a rapid return to basal levels by 1 min. This response was primarily the result of the mobilization of Ca2+ from intracellular stores since it was not affected by a concentration (20 microM) of verapamil that completely prevented the activation of CaM kinase II by glucose. Surprisingly, carbachol added prior to, or simultaneously with, glucose attenuated nutrient activation of CaM kinase II. This effect was mimicked by cholecystokinin-8 (CCK-8) and thapsigargin, suggesting its mediation by phospholipase C and the mobilization of intracellular Ca2+. In contrast, carbachol, CCK-8 and thapsigargin markedly potentiated glucose (12 mM)-induced insulin secretion. These results suggest that CaM kinase II activation can be temporally dissociated from insulin secretion but do not exclude the potential dependence of insulin exocytosis on CaM kinase II-mediated protein phosphorylation.
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Affiliation(s)
- E L Babb
- Department of Biochemistry and Molecular Biology, University of North Texas Health Science Center at Fort Worth 76107-2699, USA
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18
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Abstract
This review summarises briefly studies performed in the last 5-6 years concerning the role of second messengers in the regulation of insulin secretion, using intact and electrically permeabilized rat islets of Langerhans. It is concluded that cyclic AMP (through protein kinase A), calcium (through calcium-calmodulin dependent protein kinases) and diacylglycerol (through protein kinase C) may be important second messengers in modulating the effects of specific secretagogues on insulin release. However, recent studies strongly suggest that neither protein kinase A nor protein kinase C are directly involved in the regulation of insulin secretion by glucose. The possible involvement of other second messengers, nitric oxide and arachidonic acid, in the regulation of secretion is also briefly reviewed.
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Affiliation(s)
- S L Howell
- Biomedical Sciences Division, King's College London, UK
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19
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Ashcroft FM, Proks P, Smith PA, Ammälä C, Bokvist K, Rorsman P. Stimulus-secretion coupling in pancreatic beta cells. J Cell Biochem 1994; 55 Suppl:54-65. [PMID: 7929618 DOI: 10.1002/jcb.240550007] [Citation(s) in RCA: 208] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023]
Abstract
Insulin secretion is triggered by a rise in the intracellular Ca2+ concentration that results from the activation of voltage-gated Ca2+ channels in the beta-cell plasma membrane. Multiple types of beta-cell Ca2+ channel have been identified in both electrophysiological and molecular biological studies, but it appears that the L-type Ca2+ channel plays a dominant role in regulating Ca2+ influx. Activity of this channel is potentiated by protein kinases A and C and is inhibited by GTP-binding proteins, which may mediate the effects of potentiators and inhibitors of insulin secretion on Ca2+ influx, respectively. The mechanisms by which elevation of intracellular Ca2+ leads to the release of insulin granules is not fully understood but appears to involve activation of Ca2+/calmodulin-dependent protein kinase. Phosphorylation by either protein kinase A or C, probably at different substrates, potentiates insulin secretion by acting at some late stage in the secretory process. There is also evidence that small GTP-binding proteins are involved in regulating exocytosis in beta cells. The identification and characterisation of the proteins involved in exocytosis in beta cells and clarification of the mechanism(s) of action of Ca2+ is clearly an important goal for the future.
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Affiliation(s)
- F M Ashcroft
- University Laboratory of Physiology, Oxford, England
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20
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Weng L, Davies M, Ashcroft SJ. Effects of cholinergic agonists on diacylglycerol and intracellular calcium levels in pancreatic beta-cells. Cell Signal 1993; 5:777-86. [PMID: 8130080 DOI: 10.1016/0898-6568(93)90038-n] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
We have studied the effects of cholinergic agonists on the rates of insulin release and the concentrations of diacylglycerol (DAG) and intracellular free Ca2+ ([Ca2+]i) in the beta-cell line MIN6. Insulin secretion was stimulated by glucose, by glibenclamide and by bombesin. In the presence of glucose, both acetylcholine (ACh) and carbachol (CCh) produced a sustained increase in the rate of insulin release which was blocked by EGTA or verapamil. The DAG content of MIN6 beta-cells was not affected by glucose. Both CCh and ACh evoked an increase in DAG which was maximal after 5 min and returned to basal after 30 min; EGTA abolished the cholinergic-induced increase in DAG. ACh caused a transient rise in [Ca2+]i which was abolished by omission of Ca2+ or by addition of devapamil. Thus, cholinergic stimulation of beta-cell insulin release is associated with changes in both [Ca2+]i and DAG. The latter change persists longer than the former and activation of protein kinase C and sensitization of the secretory process to Ca2+ may underlie the prolonged effects of cholinergic agonists on insulin release. However, a secretory response to CCh was still evident after both [Ca2+]i and DAG had returned to control values suggesting that additional mechanisms may be involved.
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Affiliation(s)
- L Weng
- Nuffield Department of Clinical Biochemistry, John Radcliffe Hospital, Headington, Oxford, U.K
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21
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Opara EC, Hubbard VS. Essential fatty acids (EFA): Role in pancreatic hormone release and concomitant metabolic effect. J Nutr Biochem 1993. [DOI: 10.1016/0955-2863(93)90085-b] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
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22
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Ganesan S, Calle R, Zawalich K, Greenawalt K, Zawalich W, Shulman GI, Rasmussen H. Immunocytochemical localization of alpha-protein kinase C in rat pancreatic beta-cells during glucose-induced insulin secretion. J Cell Biol 1992; 119:313-24. [PMID: 1400576 PMCID: PMC2289651 DOI: 10.1083/jcb.119.2.313] [Citation(s) in RCA: 62] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
To investigate the role of protein kinase C (PKC) in the regulation of insulin secretion, we visualized changes in the intracellular localization of alpha-PKC in fixed beta-cells from both isolated rat pancreatic islets and the pancreas of awake unstressed rats during glucose-induced insulin secretion. Isolated, perifused rat islets were fixed in 4% paraformaldehyde, detergent permeabilized, and labeled with a mAb specific for alpha-PKC. The labeling was visualized by confocal immunofluorescent microscopy. In isolated rat pancreatic islets perifused with 2.75 mM glucose, alpha-PKC immunostaining was primarily cytoplasmic in distribution throughout the beta-cells. In islets stimulated with 20 mM glucose, there was a significant redistribution of alpha-PKC to the cell periphery. This glucose-induced redistribution was abolished when either mannoheptulose, an inhibitor of glucose metabolism, or nitrendipine, an inhibitor of calcium influx, were added to the perifusate. We also examined changes in the intracellular distribution of alpha-PKC in the beta-cells of awake, unstressed rats that were given an intravenous infusion of glucose. Immunocytochemical analysis of pancreatic sections from these rats demonstrated a glucose-induced translocation of alpha-PKC to the cell periphery of the beta-cells. These results demonstrate that the metabolism of glucose can induce the redistribution of alpha-PKC to the cell periphery of beta-cells, both in isolated islets and in the intact animal, and suggest that alpha-PKC plays a role in mediating glucose-induced insulin secretion.
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Affiliation(s)
- S Ganesan
- Department of Cell Biology, Yale University School of Medicine, New Haven, Connecticut
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23
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Abstract
In human diabetes, inherent impaired insulin secretion can be exacerbated by desensitization of the beta cell by chronic hyperglycemia. Interest in this phenomenon has generated extensive studies in genetic or experimentally induced diabetes in animals and in fully in vitro systems, with often conflicting results. In general, although chronic glucose causes decreased beta-cell response to this carbohydrate, basal response and response to alternate stimulating agents are enhanced. Glucose-stimulated insulin synthesis can be increased or decreased depending on the system studied. Using a two-compartment beta-cell model of phasic insulin secretion, a unifying hypothesis is described which can explain some of the apparent conflicting data. This hypothesis suggests that glucose-desensitization is caused by an impairment in stimulation of a hypothetical potentiator singularly responsible for: 1) some of the characteristic phases of insulin secretion; 2) basal release; 3) potentiation of non-glucose stimulators; and 4) apparent "recovery" from desensitization. Review of some of the pathways that regulate insulin secretion suggest that phosphoinositol metabolism and protein kinase-C production are regulated similarly to the theoretical potentiator and their impairment is a major contributor to glucose desensitization in the beta cell.
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Affiliation(s)
- G M Grodsky
- Metabolic Research Unit, University of California, San Francisco 94143
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24
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Persaud SJ, Jones PM, Howell SL. Activation of protein kinase C is not required for glyceraldehyde-stimulated insulin secretion from rat islets. BIOCHIMICA ET BIOPHYSICA ACTA 1991; 1095:183-5. [PMID: 1932137 DOI: 10.1016/0167-4889(91)90082-9] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
Glyceraldehyde-induced insulin release from rat islets of Langerhans was not affected following down-regulation of protein kinase C (PKC) by prolonged exposure to the tumour-promoting phorbol ester, 4 beta-phorbol myristate acetate (PMA). Glyceraldehyde did not cause translocation of islet PKC under conditions in which PMA stimulated redistribution of enzyme activity. These results indicate that activation of PKC is not required for glyceraldehyde stimulation of insulin secretion from normal rat islets.
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Affiliation(s)
- S J Persaud
- Biomedical Sciences Division, King's College London, U.K
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