scholarly journals The digitonin-permeabilized pancreatic islet model. Effect of myo-inositol 1,4,5-trisphosphate on Ca2+ mobilization

1985 ◽  
Vol 227 (3) ◽  
pp. 965-969 ◽  
Author(s):  
B A Wolf ◽  
P G Comens ◽  
K E Ackermann ◽  
W R Sherman ◽  
M L McDaniel
Keyword(s):  
Endoplasmic Reticulum ◽  
Insulin Secretion ◽  
Insulin Release ◽  
Pancreatic Islet ◽  
Second Messenger ◽  
Inositol 1 ◽  
Rapid Release ◽  
Inositol 1,4,5 Trisphosphate

Glucose-induced insulin secretion is thought to be mediated by submicromolar increases in intracellular Ca2+, although the intracellular processes are not well understood. We have used the previously characterized digitonin-permeabilized insulin-secreting pancreatic islet model to study the role of myo-inositol 1,4,5-trisphosphate (IP3), a putative second messenger for mobilization of intracellular Ca2+. Ca2+ efflux from the endoplasmic reticulum was studied with or without vanadate present to inhibit Ca2+ reuptake. IP3 (10 microM), at a free Ca2+ level of 0.06 microM, increased Ca2+ release by 30% and, when vanadate was present, by 50%. Maximal and half-maximal Ca2+ release was observed at 10 microM- and 2.5 microM-IP3, respectively. IP3 provoked a rapid release that was followed by slow reuptake. Reuptake was diminished in the presence of vanadate. Inositol 1,4-bisphosphate, inositol 1-phosphate and other phosphoinositide metabolites did not have any significant effect. Because increases in Ca2+ levels in the submicromolar range have been previously shown to induce insulin release in digitonin-permeabilized islets, our results are consistent with the concept of IP3 serving as a second messenger for insulin secretion.

scholarly journals Actions of inositol phosphates on Ca2+ pools in guinea-pig hepatocytes

1984 ◽  
Vol 224 (3) ◽  
pp. 741-746 ◽  
Author(s):  
G M Burgess ◽  
R F Irvine ◽  
M J Berridge ◽  
J S McKinney ◽  
J W Putney
Keyword(s):  
Endoplasmic Reticulum ◽  
Guinea Pig ◽  
Inositol Phosphates ◽  
Second Messenger ◽  
Release Mechanism ◽  
Specific Receptor ◽  
Rapid Release ◽  
Inositol 1,4,5 Trisphosphate

In permeabilized hepatocytes, inositol 1,4,5-trisphosphate, inositol 2,4,5-trisphosphate and inositol 4,5-bisphosphate induced rapid release of Ca2+ from an ATP-dependent, non-mitochondrial vesicular pool, probably endoplasmic reticulum. The order of potency was inositol 1,4,5-trisphosphate greater than inositol 2,4,5-trisphosphate greater than inositol 4,5-bisphosphate. The Ca2+-releasing action of inositol 1,4,5-trisphosphate is not inhibited by high [Ca2+], nor is it dependent on [ATP] in the range of 50 microM-1.5 mM. These results suggest a role for inositol 1,4,5-trisphosphate as a second messenger in hormone-induced Ca2+ mobilisation, and that a specific receptor is involved in the Ca2+-release mechanism.

Increased islet blood flow in obese rats: role of the autonomic nervous system

1992 ◽  
Vol 262 (5) ◽  
pp. E736-E740 ◽  
Author(s):  
N. Atef ◽  
A. Ktorza ◽  
L. Picon ◽  
L. Penicaud
Keyword(s):  
Blood Flow ◽  
Insulin Secretion ◽  
Pancreatic Islet ◽  
Ventromedial Hypothalamus ◽  
Zucker Rats ◽  
Islet Blood Flow ◽  
Obese Rats ◽  
Increased Sensitivity ◽  
Obese Zucker Rats

Hyperinsulinemia, a main feature of both human and animal obesity, has been demonstrated to be due to both an increased sensitivity to nutrient secretagogues and an impairment of the nervous regulation of insulin secretion. Recent studies have shown that pancreatic islet blood flow increases under conditions associated with an enhanced insulin secretion. The aim of this study was to determine whether or not changes in islet blood flow are present in hyperinsulinemic obese rats. Using the nonradioactive microsphere technique, we were able to show a significantly higher islet blood flow in obese rats either of the Zucker strain or Wistar rats after lesion of the ventromedial hypothalamus than in their respective lean controls. Subdiaphragmatic vagotomy had no significant effect on basal islet blood flow of lean rats, whereas it decreased significantly that of obese Zucker rats. Conversely, clonidine, an alpha 2-adrenergic agonist, induced a higher decrease of islet blood flow in obese than in lean Zucker rats. The injection of an intravenous bolus of glucose (375 mg/kg iv) increased significantly more islet blood flow in obese than in lean Zucker rats. It is concluded that obese rats present an increased pancreatic islet blood flow, which may result, at least in part, from exaggerated parasympathetic activity and lower than normal sympathetic activity. This could participate in the hyperinsulinemia observed in these rats.

Effect of fatty acids on insulin release: role of chain length and degree of unsaturation

1994 ◽  
Vol 266 (4) ◽  
pp. E635-E639 ◽  
Author(s):  
E. C. Opara ◽  
M. Garfinkel ◽  
V. S. Hubbard ◽  
W. M. Burch ◽  
O. E. Akwari
Keyword(s):  
Fatty Acids ◽  
Insulin Secretion ◽  
Fatty Acid ◽  
Insulin Release ◽  
Glucose Concentration ◽  
Basal Insulin ◽  
Degree Of Unsaturation ◽  
Structural Differences ◽  
Basal Insulin Secretion

The purpose of the present study was to examine the role played by structural differences among fatty acids in their effect on insulin secretion by isolated perifused murine islets. Insulin secretion measured by radioimmunoassay was assessed either as total insulin output (ng.6 islets-1.20 min-1) or as percent of basal insulin secretion. Raising the glucose concentration from a basal 5.5 to 27.7 mM caused an increase of insulin output from 6.69 +/- 1.59 to 19.92 +/- 4.99 ng.6 islets-1.20 min-1 (P < 0.05) in control (untreated) islets. However, after 20-min exposure of islets to 5 mM 16:0 or 18:2, the effect of 27.7 mM glucose was enhanced or diminished, respectively. Basal insulin output (100% basal) changed to 44 +/- 10% basal (P < 0.005) with the addition of 5 mM 4:0 but was not altered when 4:0 was replaced by 6:0. Insulin output increased modestly with 5 mM 8:0 but significantly (P < 0.05) with 10:0 until a maximal of 280 +/- 24% basal with 12:0 (P < 0.01), then fell to 110 +/- 18 and 93 +/- 15% basal (P < 0.05) with 14:0 and 16:0, respectively. The addition of 5 mM 18:0 inhibited insulin secretion to 30 +/- 10% of basal (P < 0.003), and this effect was not caused by fatty acid interference with insulin assay.(ABSTRACT TRUNCATED AT 250 WORDS)

cAMP-secretion coupling is impaired in diabetic GK/Par rat β-cells: a defect counteracted by GLP-1

2011 ◽  
Vol 301 (5) ◽  
pp. E797-E806 ◽  
Author(s):  
Manuel Dolz ◽  
Jamileh Movassat ◽  
Danielle Bailbé ◽  
Hervé Le Stunff ◽  
Marie-Hélène Giroix ◽  
...  
Keyword(s):  
Insulin Secretion ◽  
Insulin Release ◽  
Camp Accumulation ◽  
Camp Content ◽  
Camp Generation ◽  
Stimulus Secretion Coupling ◽  
Glucagon Like Peptide 1 ◽  
The Relationship

cAMP-raising agents with glucagon-like peptide-1 (GLP-1) as the first in class, exhibit multiple actions that are beneficial for the treatment of type 2 diabetic (T2D) patients, including improvement of glucose-induced insulin secretion (GIIS). To gain additional insight into the role of cAMP in the disturbed stimulus-secretion coupling within the diabetic β-cell, we examined more thoroughly the relationship between changes in islet cAMP concentration and insulin release in the GK/Par rat model of T2D. Basal cAMP content in GK/Par islets was significantly higher, whereas their basal insulin release was not significantly different from that of Wistar (W) islets. Even in the presence of IBMX or GLP-1, their insulin release did not significantly change despite further enhanced cAMP accumulation in both cases. The high basal cAMP level most likely reflects an increased cAMP generation in GK/Par compared with W islets since 1) forskolin dose-dependently induced an exaggerated cAMP accumulation; 2) adenylyl cyclase (AC)2, AC3, and Gsα proteins were overexpressed; 3) IBMX-activated cAMP accumulation was less efficient and PDE-3B and PDE-1C mRNA were decreased. Moreover, the GK/Par insulin release apparatus appears less sensitive to cAMP, since GK/Par islets released less insulin at submaximal cAMP levels and required five times more cAMP to reach a maximal secretion rate no longer different from W. GLP-1 was able to reactivate GK/Par insulin secretion so that GIIS became indistinguishable from that of W. The exaggerated cAMP production is instrumental, since GLP-1-induced GIIS reactivation was lost in the presence the AC blocker 2′,5′-dideoxyadenosine. This GLP-1 effect takes place in the absence of any improvement of the [Ca2+]i response and correlates with activation of the cAMP-dependent PKA-dependent pathway.

scholarly journals Regulation of the localization and activity of inositol 1,4,5-trisphosphate 3-kinase B in intact cells by proteolysis

2005 ◽  
Vol 392 (3) ◽  
pp. 435-441 ◽  
Author(s):  
Jowie C. H. Yu ◽  
Samantha M. Lloyd-Burton ◽  
Robin F. Irvine ◽  
Michael J. Schell
Keyword(s):  
Endoplasmic Reticulum ◽  
Actin Cytoskeleton ◽  
Hela Cells ◽  
Second Messenger ◽  
Full Length ◽  
Intact Cells ◽  
Superior Efficacy ◽  
Inositol 1,4,5 Trisphosphate ◽  
Primary Astrocytes ◽  
Functional Relevance

IP3K (inositol 1,4,5-trisphosphate 3-kinase) catalyses the Ca2+-regulated phosphorylation of the second messenger Ins(1,4,5)P3, thereby inactivating the signal to release Ca2+ and generating Ins(1,3,4,5)P4. Here we have investigated the localization and activity of IP3KB and its modulation by proteolysis. We found that the N- and C-termini (either side of residue 262) of IP3KB localized predominantly to the actin cytoskeleton and ER (endoplasmic reticulum) respectively, both in COS-7 cells and in primary astrocytes. The functional relevance of this was demonstrated by showing that full-length (actin-localized) IP3KB abolished the histamine-induced Ca2+ response in HeLa cells more effectively than truncated constructs localized to the ER or cytosol. The superior efficacy of full-length IP3KB was also attenuated by disruption of the actin cytoskeleton. By transfecting COS-7 cells with double-tagged IP3KB, we show that the translocation from actin to ER may be a physiologically regulated process caused by Ca2+-modulated constitutive proteolysis in intact cells.

scholarly journals Ghrelin’s Effects on Proinflammatory Cytokine Mediated Apoptosis and Their Impact onβ-Cell Functionality

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
Author(s):  
Antonia Diaz-Ganete ◽  
Gloria Baena-Nieto ◽  
Isabel M. Lomas-Romero ◽  
Jose Francisco Lopez-Acosta ◽  
Irene Cozar-Castellano ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Insulin Secretion ◽  
Endoplasmic Reticulum Stress ◽  
Cell Mass ◽  
Slowing Down ◽  
Stress Markers ◽  
Murine Cell Line ◽  
Survival Pathways

Ghrelin is a peptidic hormone, which stimulates cell proliferation and inhibits apoptosis in several tissues, including pancreas. In preclinical stage of type 1 diabetes, proinflammatory cytokines generate a destructive environment forβ-cells known as insulitis, which results in loss ofβ-cell mass and impaired insulin secretion, leading to diabetes. Our aim was to demonstrate that ghrelin could preserveβ-cell viability, turnover rate, and insulin secretion acting as a counter balance of cytokines. In the present work we reproduced proinflammatory milieu found in insulitis stage by treating murine cell line INS-1E and rat islets with a cytokine cocktail including IL-1β, IFNγ, and TNFαand/or ghrelin. Several proteins involved in survival pathways (ERK 1/2 and Akt/PKB) and apoptosis (caspases and Bcl-2 protein family and endoplasmic reticulum stress markers) as well as insulin secretion were analyzed. Our results show that ghrelin alone has no remarkable effects onβ-cells in basal conditions, but interestingly it activates cell survival pathways, downregulates apoptotic mediators and endoplasmic reticulum stress, and restores insulin secretion in response to glucose when beta-cells are cytokine-exposed. These data suggest a potential role of ghrelin in preventing or slowing down the transition from a preclinical to clinically established diabetes by ameliorating the effects of insulitis onβ-cells.

scholarly journals Role of ERLINs in the Control of Cell Fate through Lipid Rafts

Cells ◽  
2021 ◽  
Vol 10 (9) ◽  
pp. 2408
Author(s):  
Valeria Manganelli ◽  
Agostina Longo ◽  
Vincenzo Mattei ◽  
Serena Recalchi ◽  
Gloria Riitano ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Cell Fate ◽  
Lipid Raft ◽  
Protein Markers ◽  
Ip3 Receptors ◽  
Pathological Conditions ◽  
The Family ◽  
Inositol 1,4,5 Trisphosphate ◽  
And Function

ER lipid raft-associated protein 1 (ERLIN1) and 2 (ERLIN2) are 40 kDa transmembrane glycoproteins belonging to the family of prohibitins, containing a PHB domain. They are generally localized in the endoplasmic reticulum (ER), where ERLIN1 forms a heteroligomeric complex with its closely related ERLIN2. Well-defined functions of ERLINS are promotion of ER-associated protein degradation, mediation of inositol 1,4,5-trisphosphate (IP3) receptors, processing and regulation of lipid metabolism. Until now, ERLINs have been exclusively considered protein markers of ER lipid raft-like microdomains. However, under pathophysiological conditions, they have been described within mitochondria-associated endoplasmic reticulum membranes (MAMs), tethering sites between ER and mitochondria, characterized by the presence of specialized raft-like subdomains enriched in cholesterol and gangliosides, which play a key role in the membrane scrambling and function. In this context, it is emerging that ER lipid raft-like microdomains proteins, i.e., ERLINs, may drive mitochondria-ER crosstalk under both physiological and pathological conditions by association with MAMs, regulating the two main processes underlined, survival and death. In this review, we describe the role of ERLINs in determining cell fate by controlling the “interchange” between apoptosis and autophagy pathways, considering that their alteration has a significant impact on the pathogenesis of several human diseases.

scholarly journals GTP mobilization of Ca2+ from the endoplasmic reticulum of islets. Comparison with myo-inositol 1,4,5-trisphosphate

1987 ◽  
Vol 242 (1) ◽  
pp. 137-141 ◽  
Author(s):  
B A Wolf ◽  
J Florholmen ◽  
J R Colca ◽  
M L McDaniel
Keyword(s):  
Endoplasmic Reticulum ◽  
Additive Effect ◽  
Guanine Nucleotide ◽  
Rapid Release ◽  
Inositol 1,4,5 Trisphosphate ◽  
Hydrolysis Of

The effect of the guanine nucleotide GTP on Ca2+ release from the endoplasmic reticulum of digitonin-permeabilized islets was investigated. maximal and half-maximal Ca2+ release were observed at 5 microM- and 2.5 microM-GTP respectively. GTP caused a rapid release of Ca2+ from the endoplasmic reticulum, which was complete within 1 min. GTP-induced Ca2+ release was structurally specific and required the hydrolysis of GTP. The combination of maximal concentrations of GTP (10 microM) and myo-inositol 1,4,5-trisphosphate (IP3) (10 microM) resulted in an additive effect on Ca2+ release from the endoplasmic reticulum. GDP (100 microM), which inhibits GTP-induced Ca2+ release, did not affect IP3-induced Ca2+ release. Furthermore, GTP-induced Ca2+ release was not independent on submicromolar free Ca2+ concentrations, unlike IP3-induced Ca2+ release. These observations suggest that mechanistically GTP-induced Ca2+ release is different from IP3-induced Ca2+ release from the endoplasmic reticulum.

scholarly journals Calcium Signaling in Cholangiocytes: Methods, Mechanisms, and Effects

2018 ◽  
Vol 19 (12) ◽  
pp. 3913 ◽  
Author(s):  
Michele Rodrigues ◽  
Dawidson Gomes ◽  
Michael Nathanson
Keyword(s):  
Calcium Signaling ◽  
Second Messenger ◽  
Experimental Models ◽  
Cell Type ◽  
Release Channel ◽  
Cellular Processes ◽  
Inositol 1,4,5 Trisphosphate ◽  
Regulation Of Secretion ◽  
Trisphosphate Receptor

Calcium (Ca2+) is a versatile second messenger that regulates a number of cellular processes in virtually every type of cell. The inositol 1,4,5-trisphosphate receptor (ITPR) is the only intracellular Ca2+ release channel in cholangiocytes, and is therefore responsible for Ca2+-mediated processes in these cells. This review will discuss the machinery responsible for Ca2+ signals in these cells, as well as experimental models used to investigate cholangiocyte Ca2+ signaling. We will also discuss the role of Ca2+ in the normal and abnormal regulation of secretion and apoptosis in cholangiocytes, two of the best characterized processes mediated by Ca2+ in this cell type.

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