Contribution of the endoplasmic reticulum to the glucose-induced [Ca2+]c response in mouse pancreatic islets

2002 ◽  
Vol 282 (5) ◽  
pp. E982-E991 ◽  
Author(s):  
Abdelilah Arredouani ◽  
Jean-Claude Henquin ◽  
Patrick Gilon
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Membrane Potential ◽  
Glucose Concentration ◽  
Buffering Capacity ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucose Stimulation ◽  
Mouse Pancreatic Islets ◽  
Fast Oscillations

Thapsigargin (TG), a blocker of Ca2+ uptake by the endoplasmic reticulum (ER), was used to evaluate the contribution of the organelle to the oscillations of cytosolic Ca2+ concentration ([Ca2+]c) induced by repetitive Ca2+ influx in mouse pancreatic β-cells. Because TG depolarized the plasma membrane in the presence of glucose alone, extracellular K+ was alternated between 10 and 30 mM in the presence of diazoxide to impose membrane potential (MP) oscillations. In control islets, pulses of K+, mimicking regular MP oscillations elicited by 10 mM glucose, induced [Ca2+]c oscillations whose nadir remained higher than basal [Ca2+]c. Increasing the depolarization phase of the pulses while keeping their frequency constant (to mimic the effects of a further rise of the glucose concentration on MP) caused an upward shift of the nadir of [Ca2+]c oscillations that was reproduced by raising extracellular Ca2+ (to increase Ca2+influx) without changing the pulse protocol. In TG-pretreated islets, the imposed [Ca2+]c oscillations were of much larger amplitude than in control islets and occurred on basal levels. During intermittent trains of depolarizations, control islets displayed mixed [Ca2+]c oscillations characterized by a summation of fast oscillations on top of slow ones, whereas no progressive summation of the fast oscillations was observed in TG-pretreated islets. In conclusion, the buffering capacity of the ER in pancreatic β-cells limits the amplitude of [Ca2+]c oscillations and may explain how the nadir between oscillations remains above baseline during regular oscillations or gradually increases during mixed [Ca2+]c oscillations, two types of response observed during glucose stimulation.

scholarly journals Dominant Role of Sarcoendoplasmic Reticulum Ca2+-ATPase Pump in Ca2+ Homeostasis and Exocytosis in Rat Pancreatic β-Cells

Endocrinology ◽  
2006 ◽  
Vol 147 (3) ◽  
pp. 1396-1407 ◽  
Author(s):  
Elizabeth Hughes ◽  
Andy K. Lee ◽  
Amy Tse
Keyword(s):  
Plasma Membrane ◽  
Insulin Secretion ◽  
Membrane Potential ◽  
Simultaneous Measurement ◽  
Dominant Role ◽  
Capacitance Measurement ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Serca Pump

The exocytosis of insulin-containing granules from pancreatic β-cells is tightly regulated by changes in cytosolic Ca2+ concentration ([Ca2+]i). We investigated the role of the sarcoendoplasmic reticulum Ca2+-ATPase (SERCA) pump, Na+/Ca2+ exchanger, and plasma membrane Ca2+-ATPase pump in the Ca2+ dynamics of single rat pancreatic β-cells. When the membrane potential was voltage clamped at −70 mV (in 3 mm glucose at ∼22 or 35 C), SERCA pump inhibition dramatically slowed (∼4-fold) cytosolic Ca2+ clearance and caused a sustained rise in basal [Ca2+]i via the activation of capacitative Ca2+ entry. SERCA pump inhibition increased (∼1.8-fold) the amplitude of the depolarization-triggered Ca2+ transient at approximately 22 C. Inhibition of the Na+/Ca2+ exchanger or plasma membrane Ca2+-ATPase pump had only minor effects on Ca2+ dynamics. Simultaneous measurement of [Ca2+]i and exocytosis (with capacitance measurement) revealed that SERCA pump inhibition increased the magnitude of depolarization-triggered exocytosis. This enhancement in exocytosis was not due to the slowing of the cytosolic Ca2+ clearance but was closely correlated to the increase in the peak of the depolarization-triggered Ca2+ transient. When compared at similar [Ca2+]i with controls, the rise in basal [Ca2+]i during SERCA pump inhibition did not cause any enhancement in the magnitude of the ensuing depolarization-triggered exocytosis. Therefore, we conclude that in rat pancreatic β-cells, the rapid uptake of Ca2+ by SERCA pump limits the peak amplitude of depolarization-triggered [Ca2+]i rise and thus controls the amount of insulin secretion.

scholarly journals The endoplasmic reticulum-plasma membrane tethering protein TMEM24 is a regulator of cellular Ca2+ homeostasis

2021 ◽  
Author(s):  
Beichen Xie ◽  
Styliani Panagiotou ◽  
Jing Cen ◽  
Patrick Gilon ◽  
Peter Bergsten ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Plasma Membrane ◽  
Insulin Secretion ◽  
Lipid Transfer Protein ◽  
Underlying Mechanism ◽  
Lipid Transfer ◽  
Β Cells ◽  
Transfer Protein ◽  
Lipid Exchange ◽  
Membrane Tethering

Endoplasmic reticulum (ER) - plasma membrane (PM) contacts are sites of lipid exchange and Ca2+ transport, and both lipid transport proteins and Ca2+ channels specifically accumulate at these locations. In pancreatic β-cells, both lipid- and Ca2+ signaling are essential for insulin secretion. The recently characterized lipid transfer protein TMEM24 dynamically localize to ER-PM contact sites and provide phosphatidylinositol, a precursor of PI(4)P and PI(4,5)P2, to the plasma membrane. β-cells lacking TMEM24 exhibit markedly suppressed glucose-induced Ca2+ oscillations and insulin secretion but the underlying mechanism is not known. We now show that TMEM24 only weakly interact with the PM, and dissociates in response to both diacylglycerol and nanomolar elevations of cytosolic Ca2+. Release of TMEM24 into the bulk ER membrane also enables direct interactions with mitochondria, and we report that loss of TMEM24 results in excessive accumulation of Ca2+ in both the ER and mitochondria and in impaired mitochondria function.

scholarly journals Mitochondrial–Endoplasmic Reticulum Interplay: A Lifelong On–Off Relationship?

Contact ◽  
2019 ◽  
Vol 2 ◽  
pp. 251525641986122 ◽  
Author(s):  
Corina T. Madreiter-Sokolowski ◽  
Roland M. Malli ◽  
Wolfgang F. Graier
Keyword(s):  
Endoplasmic Reticulum ◽  
Adenosine Triphosphate ◽  
Therapeutic Strategies ◽  
Mitochondrial Activity ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Potential Target ◽  
Pathological Conditions ◽  
Elevated Glucose ◽  
Stimulation Of

This article comments recent publications that highlight an intriguing importance of specific settings in the interaction between the mitochondria and the endoplasmic reticulum to ensure cell-specific functions like the responsiveness to elevated glucose in pancreatic β-cells. Hence, alterations of the mitochondria–endoplasmic reticulum communications under various pathological conditions like aging or cancer often come with enhanced Ca2+ transfer that, in turn, yields stimulation of basal mitochondrial activity to meet the increasing adenosine triphosphate demand of the very cell. Such observations identify mitochondria-associated membranes as potential target for new therapeutic strategies against aging or cancer.

scholarly journals Glucagon-Like Peptide-1 Agonists Protect Pancreatic β-Cells From Lipotoxic Endoplasmic Reticulum Stress Through Upregulation of BiP and JunB

Diabetes ◽  
2009 ◽  
Vol 58 (12) ◽  
pp. 2851-2862 ◽  
Author(s):  
Daniel A. Cunha ◽  
Laurence Ladrière ◽  
Fernanda Ortis ◽  
Mariana Igoillo-Esteve ◽  
Esteban N. Gurzov ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Endoplasmic Reticulum Stress ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Glucagon Like Peptide ◽  
Glucagon Like Peptide 1

Sirtuin-3 (SIRT3) protects pancreatic β-cells from endoplasmic reticulum (ER) stress-induced apoptosis and dysfunction

2016 ◽  
Vol 420 (1-2) ◽  
pp. 95-106 ◽  
Author(s):  
Hao-Hao Zhang ◽  
Xiao-Jun Ma ◽  
Li-Na Wu ◽  
Yan-Yan Zhao ◽  
Peng-Yu Zhang ◽  
...  
Keyword(s):  
Endoplasmic Reticulum ◽  
Er Stress ◽  
Sirtuin 3 ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Induced Apoptosis

scholarly journals The Rab27a effector exophilin7 promotes fusion of secretory granules that have not been docked to the plasma membrane

2013 ◽  
Vol 24 (3) ◽  
pp. 319-330 ◽  
Author(s):  
Hao Wang ◽  
Ray Ishizaki ◽  
Jun Xu ◽  
Kazuo Kasai ◽  
Eri Kobayashi ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Knockout Mice ◽  
Secretory Granules ◽  
Small Gtpase ◽  
Membrane Phospholipids ◽  
Β Cells ◽  
Β Cell ◽  
Pancreatic Β Cells ◽  
Insulin Granules ◽  
Insulin Exocytosis

Granuphilin, an effector of the small GTPase Rab27a, mediates the stable attachment (docking) of insulin granules to the plasma membrane and inhibits subsequent fusion of docked granules, possibly through interaction with a fusion-inhibitory Munc18-1/syntaxin complex. However, phenotypes of insulin exocytosis differ considerably between Rab27a- and granuphilin-deficient pancreatic β cells, suggesting that other Rab27a effectors function in those cells. We found that one of the putative Rab27a effector family proteins, exophilin7/JFC1/Slp1, is expressed in β cells; however, unlike granuphilin, exophilin7 overexpressed in the β-cell line MIN6 failed to show granule-docking or fusion-inhibitory activity. Furthermore, exophilin7 has no affinities to either Munc18-1 or Munc18-1–interacting syntaxin-1a, in contrast to granuphilin. Although β cells of exophilin7-knockout mice show no apparent abnormalities in intracellular distribution or in ordinary glucose-induced exocytosis of insulin granules, they do show impaired fusion in response to some stronger stimuli, specifically from granules that have not been docked to the plasma membrane. Exophilin7 appears to mediate the fusion of undocked granules through the affinity of its C2A domain toward the plasma membrane phospholipids. These findings indicate that the two Rab27a effectors, granuphilin and exophilin7, differentially regulate the exocytosis of either stably or minimally docked granules, respectively.

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