Methyl pyruvate initiates membrane depolarization and insulin release by metabolic factors other than ATP

2001 ◽  
Vol 354 (2) ◽  
pp. 345-350 ◽  
Author(s):  
Nicolas LEMBERT ◽  
Heidrun C. JOOS ◽  
Lars-Åke IDAHL ◽  
Hermann P. T. AMMON ◽  
Martin A. WAHL
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Membrane Depolarization ◽  
Maximal Effect ◽  
Dependent Manner ◽  
Β Cell ◽  
Concentration Dependent Manner ◽  
Atp Production ◽  
Stimulus Secretion Coupling ◽  
Methyl Pyruvate

The role of mitochondria in stimulus–secretion coupling of pancreatic β-cells was examined using methyl pyruvate (MP). MP stimulated insulin secretion in the absence of glucose, with maximal effect at 5mM. K+ (30mM) alone, or in combination with diazoxide (100µM), failed to enhance MP-induced secretion. Diazoxide (100µM) inhibited MP-induced insulin secretion. MP depolarized the β-cell in a concentration-dependent manner (5–20mM). The sustained depolarization induced by 20mM MP was not influenced by 100µM diazoxide, but the continuous spiking activity was suppressed by 500µM diazoxide. Pyruvate failed to initiate insulin release (5–20mM) or to depolarize the membrane potential. ATP production in isolated β-cell mitochondria was detected as accumulation of ATP in the medium during incubation in the presence of malate or glutamate in combination with pyruvate or MP. There was no difference in ATP production induced by pyruvate/malate or MP/malate in isolated β-cell mitochondria. ATP production by MP/glutamate was higher than that induced by pyruvate/glutamate, but it was much lower than that induced by α-ketoisocaproate/glutamate. Pyruvate (5mM) or MP (5mM) had no effect on the ATP/ADP ratio in whole islets, whereas glucose (20mM) significantly increased the whole islet ATP/ADP ratio. It is concluded that MP-induced β-cell membrane depolarization or insulin release does not relate directly to mitochondrial ATP production. Instead MP may exert a direct extramitochondrial effect, or it may stimulate β-cell mitochondria to produce coupling factors different from ATP to initiate insulin release.

Chronic fetal hypoglycemia inhibits the later steps of stimulus-secretion coupling in pancreatic β-cells

2007 ◽  
Vol 292 (5) ◽  
pp. E1256-E1264 ◽  
Author(s):  
Paul J. Rozance ◽  
Sean W. Limesand ◽  
Gary O. Zerbe ◽  
William W. Hay
Keyword(s):  
Endoplasmic Reticulum ◽  
Insulin Secretion ◽  
Pancreatic Islet ◽  
Membrane Depolarization ◽  
Calcium Entry ◽  
Late Gestation ◽  
Β Cells ◽  
Β Cell ◽  
Stimulus Secretion Coupling ◽  
The Impact

We measured the impact of chronic late gestation hypoglycemia on pancreatic islet structure and function to determine the cause of decreased insulin secretion in this sheep model of fetal nutrient deprivation. Late gestation hypoglycemia did not decrease pancreas weight, insulin content, β-cell area, β-cell mass, or islet size. The pancreatic islet isolation procedure selected a group of islets that were larger and had an increased proportion of β-cells compared with islets measured in pancreatic sections, but there were no morphologic differences between islets isolated from control and hypoglycemic fetuses. The rates of glucose-stimulated pancreatic islet glucose utilization (126.2 ± 25.3 pmol glucose·islet−1·h−1, hypoglycemic, vs. 93.5 ± 5.5 pmol glucose·islet−1·h−1, control, P = 0.47) and oxidation (10.5 ± 1.7 pmol glucose·islet−1·h−1, hypoglycemic, vs. 10.6 ± 1.6 pmol glucose·islet−1·h−1, control) were not different in hypoglycemic fetuses compared with control fetuses. Chronic late gestation hypoglycemia decreased insulin secretion in isolated pancreatic islets by almost 70% in response to direct nonnutrient membrane depolarization and in response to increased extracellular calcium entry. β-Cell ultrastructure was abnormal with markedly distended rough endoplasmic reticulum in three of the seven hypoglycemic fetuses studied, but in vitro analysis of hypoglycemic control islets showed no evidence that these changes represented endoplasmic reticulum stress, as measured by transcription of glucose regulatory protein-78 and processing of X-box binding protein-1. In conclusion, these studies show that chronic hypoglycemia in late gestation decreases insulin secretion by inhibiting the later steps of stimulus-secretion coupling after glucose metabolism, membrane depolarization, and calcium entry.

Insulin secretion and differential gene expression in glucose-responsive and -unresponsive MIN6 sublines

2000 ◽  
Vol 279 (4) ◽  
pp. E773-E781 ◽  
Author(s):  
Kohtaro Minami ◽  
Hideki Yano ◽  
Takashi Miki ◽  
Kazuaki Nagashima ◽  
Chang-Zheng Wang ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Response ◽  
Lactate Production ◽  
Resting Membrane Potential ◽  
Dependent Manner ◽  
Channel Activity ◽  
Β Cells ◽  
Concentration Dependent Manner ◽  
Lactate Dehydrogenase Activity ◽  
Atp Production

We have established two sublines derived from the insulin-secreting mouse pancreatic β-cell line MIN6, designated m9 and m14. m9 Cells exhibit glucose-induced insulin secretion in a concentration-dependent manner, whereas m14 cells respond poorly to glucose. In m14 cells, glucose consumption and lactate production are enhanced, and ATP production is largely through nonoxidative pathways. Moreover, lactate dehydrogenase activity is increased, and hexokinase replaces glucokinase as a glucose-phosphorylating enzyme. The ATP-sensitive K+channel activity and voltage-dependent calcium channel activity in m14 cells are reduced, and the resting membrane potential is significantly higher than in m9 cells. Thus, in contrast to m9, a model for β-cells with normal insulin response, m14 is a model for β-cells with impaired glucose-induced insulin secretion. By mRNA differential display of these sublines, we found 10 genes to be expressed at markedly different levels. These newly established MIN6 cell sublines should be useful tools in the analysis of the genetic and molecular basis of impaired glucose-induced insulin secretion.

scholarly journals Galparan: A Powerful Insulin-Releasing Chimeric Peptide Acting at a Novel Site*

Endocrinology ◽  
1997 ◽  
Vol 138 (8) ◽  
pp. 3308-3313 ◽  
Author(s):  
Claes-Göran Östenson ◽  
Sergei Zaitsev ◽  
Per-Olof Berggren ◽  
Suad Efendic ◽  
Ülo Langel ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
B Cells ◽  
Insulin Release ◽  
Peptide Bond ◽  
Dependent Manner ◽  
Gk Rats ◽  
Chimeric Peptide ◽  
Stimulus Secretion Coupling ◽  
Dose Dependent ◽  
Distal Site

Abstract Galparan is a 27-amino acid long chimeric peptide, GWTLNSAGYLLGP-INLKALAALAKKIL amide, consisting of galanin-(1–13) linked to mastoparan amide via a peptide bond to provide the mastoparan and galanin effector parts of the molecules. Galparan (10μ m) powerfully stimulates insulin secretion from isolated rat pancreatic islets in a reversible and dose-dependent manner; the stimulation is 26-fold at 3.3 mm glucose and 6-fold at 16.7 mm glucose. Galparan also enhances insulin secretion to a similar extent from islets of diabetic GK rats. The stimulatory effect of galparan on insulin release is not directly dependent on extracellular Ca2+, nor can it be explained only by changes in free cytosolic Ca2+ concentrations. Furthermore, galparan is effective in evoking insulin release in B cells depolarized by 25 mm KCl when ATP-sensitive K+ channels are kept open by diazoxide. Thus, galparan, like mastoparan, stimulates exocytosis of insulin at a distal site in the stimulus-secretion coupling of the B cell. This distal site is not identical to that used by mastoparan, as pertussis toxin pretreatment does not influence the insulinogenic effect of galparan. In conclusion, galparan evokes a large and reversible insulin secretion, acting at a yet unknown distal site and also promoting exocytosis in depolarized B cells from normal rats as well as diabetic GK rats.

Perspective: emerging evidence for signaling roles of mitochondrial anaplerotic products in insulin secretion

2005 ◽  
Vol 288 (1) ◽  
pp. E1-E15 ◽  
Author(s):  
Michael J. MacDonald ◽  
Leonard A. Fahien ◽  
Laura J. Brown ◽  
Noaman M. Hasan ◽  
Julian D. Buss ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Citric Acid ◽  
Insulin Release ◽  
Citric Acid Cycle ◽  
Electrical Potential ◽  
Glycolytic Flux ◽  
Β Cell ◽  
Acetyl Coa ◽  
Acid Cycle ◽  
Atp Production

The importance of mitochondrial biosynthesis in stimulus secretion coupling in the insulin-producing β-cell probably equals that of ATP production. In glucose-induced insulin secretion, the rate of pyruvate carboxylation is very high and correlates more strongly with the glucose concentration the β-cell is exposed to (and thus with insulin release) than does pyruvate decarboxylation, which produces acetyl-CoA for metabolism in the citric acid cycle to produce ATP. The carboxylation pathway can increase the levels of citric acid cycle intermediates, and this indicates that anaplerosis, the net synthesis of cycle intermediates, is important for insulin secretion. Increased cycle intermediates will alter mitochondrial processes, and, therefore, the synthesized intermediates must be exported from mitochondria to the cytosol (cataplerosis). This further suggests that these intermediates have roles in signaling insulin secretion. Although evidence is quite good that all physiological fuel secretagogues stimulate insulin secretion via anaplerosis, evidence is just emerging about the possible extramitochondrial roles of exported citric acid cycle intermediates. This article speculates on their potential roles as signaling molecules themselves and as exporters of equivalents of NADPH, acetyl-CoA and malonyl-CoA, as well as α-ketoglutarate as a substrate for hydroxylases. We also discuss the “succinate mechanism,” which hypothesizes that insulin secretagogues produce both NADPH and mevalonate. Finally, we discuss the role of mitochondria in causing oscillations in β-cell citrate levels. These parallel oscillations in ATP and NAD(P)H. Oscillations in β-cell plasma membrane electrical potential, ATP/ADP and NAD(P)/NAD(P)H ratios, and glycolytic flux are known to correlate with pulsatile insulin release. Citrate oscillations might synchronize oscillations of individual mitochondria with one another and mitochondrial oscillations with oscillations in glycolysis and, therefore, with flux of pyruvate into mitochondria. Thus citrate oscillations may synchronize mitochondrial ATP production and anaplerosis with other cellular oscillations.

scholarly journals Vitamin B6 deficiency disrupts serotonin signaling in pancreatic islets and induces gestational diabetes in mice

2021 ◽  
Vol 4 (1) ◽  
Author(s):  
Ashley M. Fields ◽  
Kevin Welle ◽  
Elaine S. Ho ◽  
Clementina Mesaros ◽  
Martha Susiarjo
Keyword(s):  
Cell Proliferation ◽  
Insulin Secretion ◽  
Pancreatic Islets ◽  
Glucose Intolerance ◽  
Vitamin B6 ◽  
Serotonin Receptor ◽  
Dependent Manner ◽  
Β Cell ◽  
Vitamin B6 Deficiency ◽  
Maternal Glucose

AbstractIn pancreatic islets, catabolism of tryptophan into serotonin and serotonin receptor 2B (HTR2B) activation is crucial for β-cell proliferation and maternal glucose regulation during pregnancy. Factors that reduce serotonin synthesis and perturb HTR2B signaling are associated with decreased β-cell number, impaired insulin secretion, and gestational glucose intolerance in mice. Albeit the tryptophan-serotonin pathway is dependent on vitamin B6 bioavailability, how vitamin B6 deficiency impacts β-cell proliferation during pregnancy has not been investigated. In this study, we created a vitamin B6 deficient mouse model and investigated how gestational deficiency influences maternal glucose tolerance. Our studies show that gestational vitamin B6 deficiency decreases serotonin levels in maternal pancreatic islets and reduces β-cell proliferation in an HTR2B-dependent manner. These changes were associated with glucose intolerance and insulin resistance, however insulin secretion remained intact. Our findings suggest that vitamin B6 deficiency-induced gestational glucose intolerance involves additional mechanisms that are complex and insulin independent.

scholarly journals PDX1LOW MAFALOW β-cells contribute to islet function and insulin release

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Daniela Nasteska ◽  
Nicholas H. F. Fine ◽  
Fiona B. Ashford ◽  
Federica Cuozzo ◽  
Katrina Viloria ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Metabolic Stress ◽  
Human Islets ◽  
Islet Function ◽  
Β Cells ◽  
Β Cell ◽  
Ionic Fluxes ◽  
Transcriptomic Level ◽  
Adult Islet

AbstractTranscriptionally mature and immature β-cells co-exist within the adult islet. How such diversity contributes to insulin release remains poorly understood. Here we show that subtle differences in β-cell maturity, defined using PDX1 and MAFA expression, contribute to islet operation. Functional mapping of rodent and human islets containing proportionally more PDX1HIGH and MAFAHIGH β-cells reveals defects in metabolism, ionic fluxes and insulin secretion. At the transcriptomic level, the presence of increased numbers of PDX1HIGH and MAFAHIGH β-cells leads to dysregulation of gene pathways involved in metabolic processes. Using a chemogenetic disruption strategy, differences in PDX1 and MAFA expression are shown to depend on islet Ca2+ signaling patterns. During metabolic stress, islet function can be restored by redressing the balance between PDX1 and MAFA levels across the β-cell population. Thus, preserving heterogeneity in PDX1 and MAFA expression, and more widely in β-cell maturity, might be important for the maintenance of islet function.

scholarly journals Reducing Glucokinase Activity Restores Endogenous Pulsatility and Enhances Insulin Secretion in Islets From db/db Mice

Endocrinology ◽  
2018 ◽  
Vol 159 (11) ◽  
pp. 3747-3760 ◽  
Author(s):  
Ishrat Jahan ◽  
Kathryn L Corbin ◽  
Avery M Bogart ◽  
Nicholas B Whitticar ◽  
Christopher D Waters ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Opposite Effect ◽  
Glucose Sensing ◽  
Β Cell ◽  
Left Shift ◽  
Low Glucose ◽  
Mouse Islets ◽  
Secretion Rates

Abstract An early sign of islet failure in type 2 diabetes (T2D) is the loss of normal patterns of pulsatile insulin release. Disruptions in pulsatility are associated with a left shift in glucose sensing that can cause excessive insulin release in low glucose (relative hyperinsulinemia, a hallmark of early T2D) and β-cell exhaustion, leading to inadequate insulin release during hyperglycemia. Our hypothesis was that reducing excessive glucokinase activity in diabetic islets would improve their function. Isolated mouse islets were exposed to glucose and varying concentrations of the glucokinase inhibitor d-mannoheptulose (MH) to examine changes in intracellular calcium ([Ca2+]i) and insulin secretion. Acutely exposing islets from control CD-1 mice to MH in high glucose (20 mM) dose dependently reduced the size of [Ca2+]i oscillations detected by fura-2 acetoxymethyl. Glucokinase activation in low glucose (3 mM) had the opposite effect. We then treated islets from male and female db/db mice (age, 4 to 8 weeks) and heterozygous controls overnight with 0 to 10 mM MH to determine that 1 mM MH produced optimal oscillations. We then used 1 mM MH overnight to measure [Ca2+]i and insulin simultaneously in db/db islets. MH restored oscillations and increased insulin secretion. Insulin secretion rates correlated with MH-induced increases in amplitude of [Ca2+]i oscillations (R2 = 0.57, P < 0.01, n = 10) but not with mean [Ca2+]i levels in islets (R2 = 0.05, not significant). Our findings show that correcting glucose sensing can restore proper pulsatility to diabetic islets and improved pulsatility correlates with enhanced insulin secretion.

Direct effect of parathyroid hormone on insulin secretion from pancreatic islets

1990 ◽  
Vol 258 (6) ◽  
pp. E975-E984 ◽  
Author(s):  
G. Z. Fadda ◽  
M. Akmal ◽  
L. G. Lipson ◽  
S. G. Massry
Keyword(s):  
Insulin Secretion ◽  
Parathyroid Hormone ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Direct Effect ◽  
Indirect Evidence ◽  
Cytosolic Calcium ◽  
Dependent Manner ◽  
Stimulation Of

Indirect evidence indicates that parathyroid hormone (PTH) interacts with pancreatic islets and modulates their insulin secretion. This property of PTH has been implicated in the genesis of impaired insulin release in chronic renal failure. We examined the direct effect of PTH-(1-84) and PTH-(1-34) on insulin release using in vitro static incubation and dynamic perifusion of pancreatic islets from normal rats. Both moieties of the hormone stimulated in a dose-dependent manner glucose-induced insulin release but higher doses inhibited glucose-induced insulin release. This action of PTH was modulated by the calcium concentration in the media. The stimulatory effect of PTH was abolished by its inactivation and blocked by its antagonist [Tyr-34]bPTH-(7-34)NH2. PTH also augmented phorbol ester (TPA)-induced insulin release, stimulated adenosine 3',5'-cyclic monophosphate (cAMP) generation by pancreatic islets, and significantly increased (+50 +/- 2.7%, P less than 0.01) their cytosolic calcium. Verapamil inhibited the stimulatory effect of PTH on insulin release. The data show that 1) pancreatic islets are a PTH target and may have PTH receptors, 2) stimulation of glucose-induced insulin release by PTH is mediated by a rise in cytosolic calcium, 3) stimulation of cAMP production by PTH and a potential indirect activation of protein kinase C by PTH may also contribute to the stimulatory effect on glucose-induced insulin release, and 4) this action of PTH requires calcium in incubation or perifusion media.

Nitric oxide donor SIN-1 inhibits insulin release

1996 ◽  
Vol 271 (4) ◽  
pp. C1098-C1102 ◽  
Author(s):  
A. Sjoholm
Keyword(s):  
Nitric Oxide ◽  
Diabetes Mellitus ◽  
Protein Kinase C ◽  
Insulin Secretion ◽  
Protein Kinase ◽  
Beta Cell ◽  
Pancreatic Islets ◽  
Insulin Release ◽  
Kinase C ◽  
Stimulus Secretion Coupling

Preceding the onset of insulin-dependent diabetes mellitus, pancreatic islets are infiltrated by macrophages secreting interleukin-1 beta, which exerts cytotoxic and inhibitory actions on islet beta-cell insulin secretion through induction of nitric oxide (NO) synthesis. The influence of the NO donor 3-morpholinosydnonimine (SIN-1) on insulin secretion from isolated pancreatic islets in response to various secretagogues was investigated. Stimulation of insulin release evoked by glucose, phospholipase C activation with carbachol, and protein kinase C activation with phorbol ester were obtained by SIN-1, whereas the response to adenylyl cyclase activation or K(+)-induced depolarization was not affected. It is concluded that enzymes involved in glucose catabolism, phospholipase C or protein kinase C, may be targeted by NO. Reversal of SIN-1 inhibition of glucose-stimulated insulin release by dithiothreitol suggests that NO may inhibit insulin secretion partly by S-nitrosylation of thiol residues in key proteins in the stimulus-secretion coupling. These adverse effects of NO on the beta-cell stimulus-secretion coupling may be of importance for the development of the impaired insulin secretion characterizing diabetes mellitus.

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