scholarly journals Sequential exocytosis of insulin granules is associated with redistribution of SNAP25

2004 ◽  
Vol 165 (2) ◽  
pp. 255-262 ◽  
Author(s):  
Noriko Takahashi ◽  
Hiroyasu Hatakeyama ◽  
Haruo Okado ◽  
Akiko Miwa ◽  
Takuya Kishimoto ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Fluorescent Protein ◽  
Snare Protein ◽  
Β Cells ◽  
Fluorescent Tracer ◽  
Two Photon ◽  
Sulforhodamine B ◽  
Photon Excitation ◽  
Insulin Granules ◽  
Enhanced Cyan Fluorescent Protein

We have investigated sequential exocytosis in β cells of intact pancreatic islets with the use of two-photon excitation imaging of a polar fluorescent tracer, sulforhodamine B, and a fusion protein comprising enhanced cyan fluorescent protein (ECFP) and the SNARE protein SNAP25 (synaptosome-associated protein of 25 kD) transfected with an adenoviral vector. Sequential exocytosis was found to account for <10% of exocytic events in β cells stimulated either with glucose under various conditions or by photolysis of a caged-Ca2+ compound. Multigranular exocytosis, in which granule-to-granule fusion occurs before exocytosis, was rarely found. We detected redistribution of ECFP-SNAP25 from the plasma membrane into the membrane of the fused granule occurred in a large proportion (54%) of sequential exocytic events but in only a small fraction (5%) of solitary fusion events. Removal of cholesterol in the plasma membrane by methyl-β-cyclodextrin facilitated both redistribution of ECFP-SNAP25 and sequential exocytosis by threefold. These observations support the hypothesis that SNAP25 is a plasma membrane factor that is responsible for sequential exocytosis.

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.

scholarly journals Secretory-granule dynamics visualized in vivo with a phogrin–green fluorescent protein chimaera

1998 ◽  
Vol 333 (1) ◽  
pp. 193-199 ◽  
Author(s):  
Aristea E. POULI ◽  
Evaggelia EMMANOUILIDOU ◽  
Chao ZHAO ◽  
Christina WASMEIER ◽  
John C. HUTTON ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Green Fluorescent Protein ◽  
Pc12 Cells ◽  
Secretory Granule ◽  
Fluorescent Protein ◽  
Secretory Granules ◽  
Dense Core ◽  
Β Cells ◽  
Green Fluorescent ◽  
Insulinoma Cells

To image the behaviour in real time of single secretory granules in neuroendocrine cells we have expressed cDNA encoding a fusion construct between the dense-core secretory-granule-membrane glycoprotein, phogrin (phosphatase on the granule of insulinoma cells), and enhanced green fluorescent protein (EGFP). Expressed in INS-1 β-cells and pheochromocytoma PC12 cells, the chimaera was localized efficiently (up to 95%) to dense-core secretory granules (diameter 200–1000 nm), identified by co-immunolocalization with anti-(pro-)insulin antibodies in INS-1 cells and dopamine β-hydroxylase in PC12 cells. Using laser-scanning confocal microscopy and digital image analysis, we have used this chimaera to monitor the effects of secretagogues on the dynamics of secretory granules in single living cells. In unstimulated INS-1 β-cells, granule movement was confined to oscillatory movement (dithering) with period of oscillation 5–10 s and mean displacement < 1 µm. Both elevated glucose concentrations (30 mM), and depolarization of the plasma membrane with K+, provoked large (5–10 µm) saltatory excursions of granules across the cell, which were never observed in cells maintained at low glucose concentration. By contrast, long excursions of granules occurred in PC12 cells without stimulation, and occurred predominantly from the cell body towards the cell periphery and neurite extensions. Purinergic-receptor activation with ATP provoked granule movement towards the membrane of PC12 cells, resulting in the transfer of fluorescence to the plasma membrane consistent with fusion of the granule and diffusion of the chimaera in the plasma membrane. These results illustrate the potential use of phogrin–EGFP chimeras in the study of secretory-granule dynamics, the regulation of granule–cytoskeletal interactions and the trafficking of a granule-specific transmembrane protein during the cycle of exocytosis and endocytosis.

scholarly journals Mechanisms and Physiological Significance of the Cholinergic Control of Pancreatic β-Cell Function

2001 ◽  
Vol 22 (5) ◽  
pp. 565-604 ◽  
Author(s):  
Patrick Gilon ◽  
Jean-Claude Henquin
Keyword(s):  
Plasma Membrane ◽  
Cell Function ◽  
Β Cells ◽  
Insulin Granules ◽  
M3 Receptors ◽  
Voltage Dependent ◽  
Β Cell Function ◽  
Insulinotropic Effect ◽  
Ca2 Channels ◽  
Glucose Dependence

Abstract Acetylcholine (ACh), the major parasympathetic neurotransmitter, is released by intrapancreatic nerve endings during the preabsorptive and absorptive phases of feeding. In β-cells, ACh binds to muscarinic M3 receptors and exerts complex effects, which culminate in an increase of glucose (nutrient)-induced insulin secretion. Activation of PLC generates diacylglycerol. Activation of PLA2 produces arachidonic acid and lysophosphatidylcholine. These phospholipid-derived messengers, particularly diacylglycerol, activate PKC, thereby increasing the efficiency of free cytosolic Ca2+ concentration ([Ca2+]c) on exocytosis of insulin granules. IP3, also produced by PLC, causes a rapid elevation of [Ca2+]c by mobilizing Ca2+ from the endoplasmic reticulum; the resulting fall in Ca2+ in the organelle produces a small capacitative Ca2+ entry. ACh also depolarizes the plasma membrane of β-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 [Ca2+]c. Surprisingly, ACh can also inhibit voltage-dependent Ca2+ channels and stimulate Ca2+ efflux when [Ca2+]c is elevated. However, under physiological conditions, the net effect of ACh on [Ca2+]c is always positive. The insulinotropic effect of ACh results from two mechanisms: one involves a rise in [Ca2+]c and the other involves a marked, PKC-mediated increase in the efficiency of Ca2+ on exocytosis. The paper also discusses the mechanisms explaining the glucose dependence of the effects of ACh on insulin release.

scholarly journals A practical method for monitoring FRET-based biosensors in living animals using two-photon microscopy

2015 ◽  
Vol 309 (11) ◽  
pp. C724-C735 ◽  
Author(s):  
Wen Tao ◽  
Michael Rubart ◽  
Jennifer Ryan ◽  
Xiao Xiao ◽  
Chunping Qiao ◽  
...  
Keyword(s):  
Cell Biology ◽  
Fluorescent Protein ◽  
Resonance Energy Transfer ◽  
Resonance Energy ◽  
Practical Method ◽  
Two Photon Microscopy ◽  
Cellular Processes ◽  
Two Photon ◽  
Photon Excitation ◽  
Wide Range

The commercial availability of multiphoton microscope systems has nurtured the growth of intravital microscopy as a powerful technique for evaluating cell biology in the relevant context of living animals. In parallel, new fluorescent protein (FP) biosensors have become available that enable studies of the function of a wide range of proteins in living cells. Biosensor probes that exploit Förster resonance energy transfer (FRET) are among the most sensitive indicators of an array of cellular processes. However, differences between one-photon and two-photon excitation (2PE) microscopy are such that measuring FRET by 2PE in the intravital setting remains challenging. Here, we describe an approach that simplifies the use of FRET-based biosensors in intravital 2PE microscopy. Based on a systematic comparison of many different FPs, we identified the monomeric (m) FPs mTurquoise and mVenus as particularly well suited for intravital 2PE FRET studies, enabling the ratiometric measurements from linked FRET probes using a pair of experimental images collected simultaneously. The behavior of the FPs is validated by fluorescence lifetime and sensitized emission measurements of a set of FRET standards. The approach is demonstrated using a modified version of the AKAR protein kinase A biosensor, first in cells in culture, and then in hepatocytes in the liver of living mice. The approach is compatible with the most common 2PE microscope configurations and should be applicable to a variety of different FRET probes.

scholarly journals Two-Photon Calcium Imaging of Network Activity in XFP-Expressing Neurons in the Mouse

2007 ◽  
Vol 97 (4) ◽  
pp. 3118-3125 ◽  
Author(s):  
Jennifer M. Wilson ◽  
Daniel A. Dombeck ◽  
Manuel Díaz-Ríos ◽  
Ronald M. Harris-Warrick ◽  
Robert M. Brownstone
Keyword(s):  
Spinal Cord ◽  
Laser Scanning ◽  
Fluorescent Protein ◽  
Laser Scanning Microscopy ◽  
Network Activity ◽  
Spatiotemporal Pattern ◽  
Two Photon ◽  
Physiological Investigation ◽  
Photon Excitation

Fluorescent protein (XFP) expression in postnatal neurons allows the anatomical and physiological investigation of identified subpopulations of interneurons with established techniques. However, the spatiotemporal pattern of activity of these XFP neurons within a network and their role in the functional output of the network are more challenging issues to investigate. Here we apply two-photon excitation laser scanning microscopy to mouse spinal cord locomotor networks and present the methodology by which calcium activity can be recorded in XFP-expressing neurons. Such activity can be studied both in relation to neighboring non-XFP neurons in a spinal cord slice preparation and in relation to functional locomotor output monitored by ventral root activity in the intact in vitro spinal cord. Thus the network properties and functional correlates with locomotion of identified populations of interneurons can be studied simultaneously.

scholarly journals TIRF imaging of docking and fusion of single insulin granule motion in primary rat pancreatic β-cells: different behaviour of granule motion between normal and Goto–Kakizaki diabetic rat β-cells

2004 ◽  
Vol 381 (1) ◽  
pp. 13-18 ◽  
Author(s):  
Mica OHARA-IMAIZUMI ◽  
Chiyono NISHIWAKI ◽  
Toshiteru KIKUTA ◽  
Shintaro NAGAI ◽  
Yoko NAKAMICHI ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Insulin Release ◽  
Secretory Granules ◽  
Dynamic Change ◽  
Second Phase ◽  
Β Cells ◽  
Gk Rat ◽  
Pancreatic Β Cells ◽  
Insulin Granules ◽  
Granule Motion

We imaged and analysed the motion of single insulin secretory granules near the plasma membrane in live pancreatic β-cells, from normal and diabetic Goto–Kakizaki (GK) rats, using total internal reflection fluorescence microscopy (TIRFM). In normal rat primary β-cells, the granules that were fusing during the first phase originate from previously docked granules, and those during the second phase originate from ‘newcomers’. In diabetic GK rat β-cells, the number of fusion events from previously docked granules were markedly reduced, and, in contrast, the fusion from newcomers was still preserved. The dynamic change in the number of docked insulin granules showed that, in GK rat β-cells, the total number of docked insulin granules was markedly decreased to 35% of the initial number after glucose stimulation. Immunohistochemistry with anti-insulin antibody observed by TIRFM showed that GK rat β-cells had a marked decline of endogenous insulin granules docked to the plasma membrane. Thus our results indicate that the decreased number of docked insulin granules accounts for the impaired insulin release during the first phase of insulin release in diabetic GK rat β-cells.

scholarly journals ELKS, a Protein Structurally Related to the Active Zone-associated Protein CAST, Is Expressed in Pancreatic β Cells and Functions in Insulin Exocytosis: Interaction of ELKS with Exocytotic Machinery Analyzed by Total Internal Reflection Fluorescence Microscopy

2005 ◽  
Vol 16 (7) ◽  
pp. 3289-3300 ◽  
Author(s):  
Mica Ohara-Imaizumi ◽  
Toshihisa Ohtsuka ◽  
Satsuki Matsushima ◽  
Yoshihiro Akimoto ◽  
Chiyono Nishiwaki ◽  
...  
Keyword(s):  
Plasma Membrane ◽  
Fluorescence Microscopy ◽  
Active Zone ◽  
Total Internal Reflection ◽  
Internal Reflection ◽  
Total Internal Reflection Fluorescence ◽  
Β Cells ◽  
Pancreatic Β Cells ◽  
Insulin Granules ◽  
Insulin Exocytosis

The cytomatrix at the active zone (CAZ) has been implicated in defining the site of Ca2+-dependent exocytosis of neurotransmitters. Here, we demonstrate the expression and function of ELKS, a protein structurally related to the CAZ protein CAST, in insulin exocytosis. The results of confocal and immunoelectron microscopic analysis showed that ELKS is present in pancreatic β cells and is localized close to insulin granules docked on the plasma membrane-facing blood vessels. Total internal reflection fluorescence microscopy imaging in insulin-producing clonal cells revealed that the ELKS clusters are less dense and unevenly distributed than syntaxin 1 clusters, which are enriched in the plasma membrane. Most of the ELKS clusters were on the docking sites of insulin granules that were colocalized with syntaxin 1 clusters. Total internal reflection fluorescence images of single-granule motion showed that the fusion events of insulin granules mostly occurred on the ELKS cluster, where repeated fusion was sometimes observed. When the Bassoon-binding region of ELKS was introduced into the cells, the docking and fusion of insulin granules were markedly reduced. Moreover, attenuation of ELKS expression by small interfering RNA reduced the glucose-evoked insulin release. These data suggest that the CAZ-related protein ELKS functions in insulin exocytosis from pancreatic β cells.

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