151
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Newton AJ, Kirchhausen T, Murthy VN. Inhibition of dynamin completely blocks compensatory synaptic vesicle endocytosis. Proc Natl Acad Sci U S A 2006; 103:17955-60. [PMID: 17093049 PMCID: PMC1693854 DOI: 10.1073/pnas.0606212103] [Citation(s) in RCA: 181] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
The ability of synapses to sustain signal propagation relies on rapid recycling of transmitter-containing presynaptic vesicles. Clathrin- and dynamin-mediated retrieval of vesicular membrane has an undisputed role in synaptic vesicle recycling. There is also evidence for other modes of vesicle retrieval, including bulk retrieval and the so-called kiss-and-run recycling. Whether dynamin in required for these other modes of synaptic vesicle endocytosis remains unclear. Here, we have tested the role of dynamin in synaptic vesicle endocytosis by using a small molecule called dynasore, which rapidly inhibits the GTPase activity of dynamin with high specificity. Endocytosis after sustained or brief stimuli was completely and reversibly blocked by dynasore in cultured hippocampal neurons expressing the fluorescent tracer synaptopHluorin. By contrast, dynasore had no effect on exocytosis. In the presence of dynasore, low-frequency stimulation led to sustained accumulation of synaptopHluorin and other vesicular proteins on the surface membrane at a rate predicted from net exocytosis. These vesicular components remained on surface membranes even after the stimulus was terminated, suggesting that all endocytic events rely on dynamin during low-frequency activity as well as in the period after it. Ultrastructural analysis revealed a reduction in the density of synaptic vesicles and the presence of endocytic structures only at synapses that were stimulated in the presence of dynasore. In sum, our data indicate that dynamin is essential for all forms of compensatory synaptic vesicle endocytosis including any kiss-and-run events.
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Affiliation(s)
- A. Jamila Newton
- *Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138; and
| | - Tom Kirchhausen
- Department of Cell Biology and CBR Institute for Biomedical Research, Harvard Medical School, Boston, MA 02115
| | - Venkatesh N. Murthy
- *Department of Molecular and Cellular Biology, Harvard University, Cambridge, MA 02138; and
- To whom correspondence should be addressed. E-mail:
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152
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Granseth B, Odermatt B, Royle SJ, Lagnado L. Clathrin-mediated endocytosis is the dominant mechanism of vesicle retrieval at hippocampal synapses. Neuron 2006; 51:773-86. [PMID: 16982422 DOI: 10.1016/j.neuron.2006.08.029] [Citation(s) in RCA: 506] [Impact Index Per Article: 28.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2006] [Revised: 08/03/2006] [Accepted: 08/28/2006] [Indexed: 10/24/2022]
Abstract
The maintenance of synaptic transmission requires that vesicles be recycled after releasing neurotransmitter. Several modes of retrieval have been proposed to operate at small synaptic terminals of central neurons, including a fast "kiss-and-run" mechanism that releases neurotransmitter through a fusion pore. Using an improved fluorescent reporter comprising pHluorin fused to synaptophysin, we find that only a slow mode of endocytosis (tau = 15 s) operates at hippocampal synapses when vesicle fusion is triggered by a single nerve impulse or short burst. This retrieval mechanism is blocked by overexpression of the C-terminal fragment of AP180 or by knockdown of clathrin using RNAi, and it is associated with the movement of clathrin and vesicle proteins out of the synapse. These results indicate that clathrin-mediated endocytosis is the major, if not exclusive, mechanism of vesicle retrieval after physiological stimuli.
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Affiliation(s)
- Björn Granseth
- MRC Laboratory of Molecular Biology, Hills Road, Cambridge, CB2 2QH, United Kingdom
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153
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He L, Wu XS, Mohan R, Wu LG. Two modes of fusion pore opening revealed by cell-attached recordings at a synapse. Nature 2006; 444:102-5. [PMID: 17065984 DOI: 10.1038/nature05250] [Citation(s) in RCA: 168] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Accepted: 09/14/2006] [Indexed: 11/09/2022]
Abstract
Fusion of a vesicle with the cell membrane opens a pore that releases transmitter to the extracellular space. The pore can either dilate fully so that the vesicle collapses completely, or close rapidly to generate 'kiss-and-run' fusion. The size of the pore determines the release rate. At synapses, the size of the fusion pore is unclear, 'kiss-and-run' remains controversial, and the ability of 'kiss-and-run' fusion to generate rapid synaptic currents is questionable. Here, by recording fusion pore kinetics during single vesicle fusion, we found both full collapse and 'kiss-and-run' fusion at calyx-type synapses. For full collapse, the initial fusion pore conductance (G(p)) was usually >375 pS and increased rapidly at > or =299 pS ms(-1). 'Kiss-and-run' fusion was seen as a brief capacitance flicker (<2 s) with G(p) >288 pS for most flickers, but within 15-288 pS for the remaining flickers. Large G(p) (>288 pS) might discharge transmitter rapidly and thereby cause rapid synaptic currents, whereas small G(p) might generate slow and small synaptic currents. These results show that 'kiss-and-run' fusion occurs at synapses and that it can generate rapid postsynaptic currents, and suggest that various fusion pore sizes help to control the kinetics and amplitude of synaptic currents.
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Affiliation(s)
- Liming He
- National Institute of Neurological Disorders and Stroke, 35 Convent Drive, Building 35, Room 2B-1012, Bethesda, Maryland 20892, USA
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154
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de Kock CPJ, Cornelisse LN, Burnashev N, Lodder JC, Timmerman AJ, Couey JJ, Mansvelder HD, Brussaard AB. NMDA receptors trigger neurosecretion of 5-HT within dorsal raphe nucleus of the rat in the absence of action potential firing. J Physiol 2006; 577:891-905. [PMID: 17053037 PMCID: PMC1890386 DOI: 10.1113/jphysiol.2006.115311] [Citation(s) in RCA: 45] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Activity and calcium-dependent release of neurotransmitters from the somatodendritic compartment is an important signalling mechanism between neurones throughout the brain. NMDA receptors and vesicles filled with neurotransmitters occur in close proximity in many brain areas. It is unknown whether calcium influx through these receptors can trigger the release of somatodendritic vesicles directly, or whether postsynaptic action potential firing is necessary for release of these vesicles. Here we addressed this question by studying local release of serotonin (5-HT) from dorsal raphé nucleus (DRN) neurones. We performed capacitance measurements to monitor the secretion of vesicles in giant soma patches, in response to short depolarizations and action potential waveforms. Amperometric measurements confirmed that secreted vesicles contained 5-HT. Surprisingly, two-photon imaging of DRN neurones in slices revealed that dendritic calcium concentration changes in response to somatic firing were restricted to proximal dendritic areas. This implied that alternative calcium entry pathways may dominate the induction of vesicle secretion from distal dendrites. In line with this, transient NMDA receptor activation, in the absence of action potential firing, was sufficient to induce capacitance changes. By monitoring GABAergic transmission onto DRN 5-HT neurones in slices, we show that endogenous NMDA receptor activation, in the absence of postsynaptic firing, induced release of 5-HT, which in turn increased the frequency of GABAergic inputs through activation of 5-HT(2) receptors. We propose here that calcium influx through NMDA receptors can directly induce postsynaptic 5-HT release from DRN neurones, which in turn may facilitate GABAergic input onto these cells.
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Affiliation(s)
- C P J de Kock
- Department of Experimental Neurophysiology, Centre for Neurogenomics and Cognitive Research, Vrije Universiteit Amsterdam, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
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155
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Fulop T, Smith C. Physiological stimulation regulates the exocytic mode through calcium activation of protein kinase C in mouse chromaffin cells. Biochem J 2006; 399:111-9. [PMID: 16784416 PMCID: PMC1570168 DOI: 10.1042/bj20060654] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Adrenal medullary chromaffin cells release catecholamines and neuropeptides in an activity-dependent manner controlled by the sympathetic nervous system. Under basal sympathetic tone, catecholamines are preferentially secreted. During acute stress, increased sympathetic firing evokes release of both catecholamines as well as neuropeptides. Both signalling molecules are co-packaged in the same large dense core granules, thus release of neuropeptide transmitters must be regulated after granule fusion with the cell surface. Previous work has indicated this may be achieved through a size-exclusion mechanism whereby, under basal sympathetic firing, the catecholamines are selectively released through a restricted fusion pore, while less-soluble neuropeptides are left behind in the dense core. Only under the elevated firing experienced during the sympathetic stress response do the granules fully collapse to expel catecholamines and neuropeptides. However, mechanistic description and physiological regulation of this process remain to be determined. We employ electrochemical amperometry, fluid-phase dye uptake and electrophysiological capacitance noise analysis to probe the fusion intermediate in mouse chromaffin cells under physiological electrical stimulation. We show that basal firing rates result in the selective release of catecholamines through an Omega-form 'kiss and run' fusion event characterized by a narrow fusion pore. Increased firing raises calcium levels and activates protein kinase C, which then promotes fusion pore dilation until full granule collapse occurs. Our results demonstrate that the transition between 'kiss and run' and 'full collapse' exocytosis serves a vital physiological regulation in neuroendocrine chromaffin cells and help effect a proper acute stress response.
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Affiliation(s)
- Tiberiu Fulop
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, U.S.A
| | - Corey Smith
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, U.S.A
- To whom correspondence should be addressed (email )
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156
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MacDonald PE, Braun M, Galvanovskis J, Rorsman P. Release of small transmitters through kiss-and-run fusion pores in rat pancreatic beta cells. Cell Metab 2006; 4:283-90. [PMID: 17011501 DOI: 10.1016/j.cmet.2006.08.011] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/30/2006] [Revised: 05/26/2006] [Accepted: 08/23/2006] [Indexed: 11/25/2022]
Abstract
Exocytosis of secretory vesicles begins with a fusion pore connecting the vesicle lumen to the extracellular space. This pore may then expand or it may close to recapture the vesicle intact. The contribution of the latter, termed kiss-and-run, to exocytosis of pancreatic beta cell large dense-core vesicles (LDCVs) is controversial. Examination of single vesicle fusion pores demonstrated that rat beta cell LDCVs can undergo exocytosis by rapid pore expansion, by the formation of stable pores, or via small transient kiss-and-run fusion pores. Elevation of cAMP shifted LDCV fusion pore openings to the transient mode. Under this condition, the small fusion pores were sufficient for release of ATP, stored within LDCVs together with insulin. Individual ATP release events occurred coincident with amperometric "stand alone feet" representing kiss-and-run. Therefore, the LDCV kiss-and-run fusion pores allow small transmitter release but likely retain the larger insulin peptide. This may represent a mechanism for selective intraislet signaling.
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Affiliation(s)
- Patrick E MacDonald
- Oxford Centre for Diabetes Endocrinology and Metabolism, University of Oxford, Churchill Hospital, Oxford OX3 7LJ, United Kingdom.
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157
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Kasai H, Kishimoto T, Nemoto T, Hatakeyama H, Liu TT, Takahashi N. Two-photon excitation imaging of exocytosis and endocytosis and determination of their spatial organization. Adv Drug Deliv Rev 2006; 58:850-77. [PMID: 16996640 DOI: 10.1016/j.addr.2006.07.008] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2006] [Accepted: 07/13/2006] [Indexed: 12/17/2022]
Abstract
Two-photon excitation imaging is the least invasive optical approach to study living tissues. We have established two-photon extracellular polar-tracer (TEP) imaging with which it is possible to visualize and quantify all exocytic events in the plane of focus within secretory tissues. This technology also enables estimate of the precise diameters of vesicles independently of the spatial resolution of the optical microscope, and determination of the fusion pore dynamics at nanometer resolution using TEP-imaging based quantification (TEPIQ). TEP imaging has been applied to representative secretory glands, e.g., exocrine pancreas, endocrine pancreas, adrenal medulla and a pheochromocytoma cell line (PC12), and has revealed unexpected diversity in the spatial organization of exocytosis and endocytosis crucial for the physiology and pathology of secretory tissues and neurons. TEP imaging and TEPIQ analysis are powerful tools for elucidating the molecular and cellular mechanisms of exocytosis and certain related diseases, such as diabetes mellitus, and the development of new therapeutic agents and diagnostic tools.
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Affiliation(s)
- Haruo Kasai
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, The University of Tokyo, Tokyo 113-0033, Japan.
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158
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Harata NC, Aravanis AM, Tsien RW. Kiss-and-run and full-collapse fusion as modes of exo-endocytosis in neurosecretion. J Neurochem 2006; 97:1546-70. [PMID: 16805768 DOI: 10.1111/j.1471-4159.2006.03987.x] [Citation(s) in RCA: 138] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Neurotransmitters and hormones are released from neurosecretory cells by exocytosis (fusion) of synaptic vesicles, large dense-core vesicles and other types of vesicles or granules. The exocytosis is terminated and followed by endocytosis (retrieval). More than fifty years of research have established full-collapse fusion and clathrin-mediated endocytosis as essential modes of exo-endocytosis. Kiss-and-run and vesicle reuse represent alternative modes, but their prevalence and importance have yet to be elucidated, especially in neurons of the mammalian CNS. Here we examine various modes of exo-endocytosis across a wide range of neurosecretory systems. Full-collapse fusion and kiss-and-run coexist in many systems and play active roles in exocytotic events. In small nerve terminals of CNS, kiss-and-run has an additional role of enabling nerve terminals to conserve scarce vesicular resources and respond to high-frequency inputs. Full-collapse fusion and kiss-and-run will each contribute to maintaining cellular communication over a wide range of frequencies.
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Affiliation(s)
- Nobutoshi C Harata
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California, USA
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159
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Abstract
Exocytosis is initiated within a highly localized region of contact between two biological membranes. Small areas of these membranes draw close, molecules on the two surfaces interact, and structural transformations take place. Membrane fusion requires the action of proteins specialized for this task, and these proteins act as a fusion machine. At a critical point in this process, a fusion pore forms within the membrane contact site and then expands as the spherical vesicle merges with the flat target membrane. Hence, the operation of a fusion machine must be realized through the formation and expansion of a fusion pore. Delineating the relation between the fusion machine and the fusion pore thus emerges as a central goal in elucidating the mechanisms of membrane fusion. We summarize present knowledge of fusion machines and fusion pores studied in vitro, in neurons, and in neuroendocrine cells, and synthesize this knowledge into some specific and detailed hypotheses for exocytosis.
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Affiliation(s)
- Meyer B Jackson
- Howard Hughes Medical Institute, 2Department of Physiology, University of Wisconsin, Madison, Wisconsin 53706, USA.
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160
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Jacobowitz DM. Differential effects of polyunsaturated fatty acids on membrane capacitance and exocytosis in rat pheochromocytoma-12 cells. Neurochem Res 2006; 31:125-6. [PMID: 16673172 DOI: 10.1007/s11064-005-9002-x] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/06/2005] [Indexed: 10/25/2022]
Abstract
The fusion of synaptic vesicles with the plasma membrane during exocytosis can be recorded by membrane capacitance measurements under voltage-clamp conditions. These measurements enable high time-resolution quantitation of exocytosis. The present study was carried out using the above technique to elucidate the effects of various polyunsaturated fatty acids on exocytosis in a neuroendocrine cell, the rat pheochromocytoma-12 (PC12) cell. External application of eicosapentaenoic acid and arachidonic acid resulted in an increase in capacitance of PC12 cells, indicating fusion of secretory vesicles with cell membranes and exocytosis. In contrast, docosahexaenoic acid, linoleic acid, oleic acid, and vehicle control had no significant effect on capacitance. The above findings show differential effects of polyunsaturated fatty acids on exocytosis in PC12 cells. It is postulated that besides arachidonic acid, eicosapentaenoic acid could also play an important role in exocytosis and neurotransmitter release, in neurons and hormone-secreting cells.
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Affiliation(s)
- David M Jacobowitz
- Laboratory of Clinical Science, National Institute of Mental Health, Bethesda, MD 20892, USA
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161
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Becherer U, Rettig J. Vesicle pools, docking, priming, and release. Cell Tissue Res 2006; 326:393-407. [PMID: 16819626 DOI: 10.1007/s00441-006-0243-z] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Accepted: 05/09/2006] [Indexed: 10/24/2022]
Abstract
The release of neurotransmitter from synaptic vesicles represents the final event by which presynapses send their chemical signal to the receiving postsynapses. Prior to fusion, synaptic vesicles undergo a series of maturation events, most notably the membrane-delimited docking and priming steps. Physiological and optical experiments with high-time resolution have allowed the distinction of vesicles in different maturation states with respect to fusion, the so-called vesicle pools. In this review, we define the various vesicle pools and discuss pathways leading into and out of these pools. We also provide an overview of an array of proteins that have been identified or are speculated to play a role in the transition between the various vesicle pools.
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Affiliation(s)
- Ute Becherer
- Universität des Saarlandes, Physiologisches Institut, Gebäude 59, Kirrberger Strasse 8, 66421, Homburg/Saar, Germany
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162
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Abstract
Research on calcium-triggered exocytosis has converged on the fusion pore as a critical kinetic intermediate. Using sensitive biophysical methods to record signals from living cells in the act of releasing neurotransmitter or hormone has provided clues about the structure and composition of fusion pores. The dynamics of fusion pore opening, closing, and dilating has revealed how specific proteins transduce a calcium binding signal to catalyze membrane fusion. The fusion pore determines how rapidly neurotransmitter is expelled from a vesicle into the synaptic cleft. This rate places constraints on the form of a synaptic response during different modes of release.
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Affiliation(s)
- Meyer B Jackson
- Department of Physiology, University of Wisconsin, Wisconsin, USA.
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163
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Nouvian R, Beutner D, Parsons T, Moser T. Structure and function of the hair cell ribbon synapse. J Membr Biol 2006; 209:153-65. [PMID: 16773499 PMCID: PMC1764598 DOI: 10.1007/s00232-005-0854-4] [Citation(s) in RCA: 149] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2006] [Indexed: 11/30/2022]
Abstract
Faithful information transfer at the hair cell afferent synapse requires synaptic transmission to be both reliable and temporally precise. The release of neurotransmitter must exhibit both rapid on and off kinetics to accurately follow acoustic stimuli with a periodicity of 1 ms or less. To ensure such remarkable temporal fidelity, the cochlear hair cell afferent synapse undoubtedly relies on unique cellular and molecular specializations. While the electron microscopy hallmark of the hair cell afferent synapse — the electron-dense synaptic ribbon or synaptic body — has been recognized for decades, dissection of the synapse’s molecular make-up has only just begun. Recent cell physiology studies have added important insights into the synaptic mechanisms underlying fidelity and reliability of sound coding. The presence of the synaptic ribbon links afferent synapses of cochlear and vestibular hair cells to photoreceptors and bipolar neurons of the retina. This review focuses on major advances in understanding the hair cell afferent synapse molecular anatomy and function that have been achieved during the past years.
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Affiliation(s)
- R. Nouvian
- InnerEarLab, Department of Otolaryngology, Goettingen University Medical School, and Center for Molecular Physiology of the Brain, Robert-Koch-Strasse 40, 37075 Goettingen, Germany
| | - D. Beutner
- InnerEarLab, Department of Otolaryngology, Goettingen University Medical School, and Center for Molecular Physiology of the Brain, Robert-Koch-Strasse 40, 37075 Goettingen, Germany
- Department of Otorhinolaryngology, Head and Neck Surgery, University of Cologne Medical School, Kerpener Straße 62, 50924 Koeln, Germany
| | - T.D. Parsons
- Clinical Studies-New Bolton Center, School of Veterinary Medicine and Otorhinolaryngology-Head and Neck Surgery, School of Medicine, University of Pennsylvania, Philadelphia, PA 19104 USA
| | - T. Moser
- InnerEarLab, Department of Otolaryngology, Goettingen University Medical School, and Center for Molecular Physiology of the Brain, Robert-Koch-Strasse 40, 37075 Goettingen, Germany
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164
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Liu W, Montana V, Bai J, Chapman ER, Mohideen U, Parpura V. Single molecule mechanical probing of the SNARE protein interactions. Biophys J 2006; 91:744-58. [PMID: 16648158 PMCID: PMC1483094 DOI: 10.1529/biophysj.105.073312] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Exocytotic release of neurotransmitters is mediated by the ternary soluble N-ethyl maleimide-sensitive fusion protein attachment protein receptors (SNAREs) complex, comprised of syntaxin (Sx), synaptosome-associated protein of 25 kDa (SNAP25), and synaptobrevin 2 (Sb2). Since exocytosis involves the nonequilibrium process of association and dissociation of bonds between molecules of the SNARE complex, dynamic measurements at the single molecule level are necessary for a detailed understanding of these interactions. To address this issue, we used the atomic force microscope in force spectroscopy mode to show from single molecule investigations of the SNARE complex, that Sx1A and Sb2 are zippered throughout their entire SNARE domains without the involvement of SNAP25. When SNAP25B is present in the complex, it creates a local interaction at the 0 (ionic) layer by cuffing Sx1A and Sb2. Force loading rate studies indicate that the ternary complex interaction is more stable than the Sx1A-Sb2 interaction.
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Affiliation(s)
- W Liu
- Department of Physics, University of California, Riverside, California 92521, USA
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165
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Elhamdani A, Azizi F, Artalejo CR. Double patch clamp reveals that transient fusion (kiss-and-run) is a major mechanism of secretion in calf adrenal chromaffin cells: high calcium shifts the mechanism from kiss-and-run to complete fusion. J Neurosci 2006; 26:3030-6. [PMID: 16540581 PMCID: PMC6673983 DOI: 10.1523/jneurosci.5275-05.2006] [Citation(s) in RCA: 121] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Transient fusion ("kiss-and-run") is accepted as a mode of transmitter release both in central neurons and neuroendocrine cells, but the prevalence of this mechanism compared with full fusion is still in doubt. Using a novel double patch-clamp method (whole cell/cell attached), permitting the recording of unitary capacitance events while stimulating under a variety of conditions including action potentials, we show that transient fusion is the predominant (>90%) mode of secretion in calf adrenal chromaffin cells. Raising intracellular Ca2+ concentration ([Ca]i) from 10 to 200 microM increases the incidence of full fusion events at the expense of transient fusion. Blocking rapid endocytosis that normally terminates transient fusion events also promotes full fusion events. Thus, [Ca]i controls the transition between transient and full fusion, each of which is coupled to different modes of endocytosis.
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Affiliation(s)
- Abdeladim Elhamdani
- Department of Pharmacology, Wayne State University School of Medicine, Detroit, Michigan 48201, USA.
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166
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Yudowski GA, Puthenveedu MA, von Zastrow M. Distinct modes of regulated receptor insertion to the somatodendritic plasma membrane. Nat Neurosci 2006; 9:622-7. [PMID: 16604070 DOI: 10.1038/nn1679] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2006] [Accepted: 03/10/2006] [Indexed: 02/06/2023]
Abstract
Many neural signaling receptors are regulated by endocytosis, but little is known about receptor insertion into the plasma membrane. Time-lapse imaging of the beta2 adrenergic receptor expressed in cultured rat hippocampal neurons, using pH-sensitive green fluorescent protein tagging and total internal reflection fluorescence microscopy, resolved distinct vesicular fusion events mediating receptor insertion into the somatodendritic plasma membrane. A 'transient' insertion mode resulted in rapid lateral dispersion of receptors immediately after insertion. A 'persistent' insertion mode resulted in the retention of inserted receptors in surface-accessible domains, which were relatively immobile for a prolonged 'wait' period before dispersing laterally. Distinct insertion modes were oppositely regulated by receptor activation and by mechanisms differing in their dependence on the signaling effector cyclic AMP-dependent protein kinase. These results reveal a new mechanism for homeostatic regulation of postsynaptic signaling and a 'kiss-and-wait' mode of regulated membrane protein insertion in neurons.
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Affiliation(s)
- Guillermo A Yudowski
- Department of Psychiatry, University of California San Francisco, 600 16th Street, San Francisco, California 94143, USA
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167
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Ting JT, Kelley BG, Sullivan JM. Synaptotagmin IV does not alter excitatory fast synaptic transmission or fusion pore kinetics in mammalian CNS neurons. J Neurosci 2006; 26:372-80. [PMID: 16407532 PMCID: PMC2100427 DOI: 10.1523/jneurosci.3997-05.2006] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptotagmin IV (Syt IV) is a brain-specific isoform of the synaptotagmin family, the levels of which are strongly elevated after seizure activity. The dominant hypothesis of Syt IV function states that Syt IV upregulation is a neuroprotective mechanism for reducing neurotransmitter release. To test this hypothesis in mammalian CNS synapses, Syt IV was overexpressed in cultured mouse hippocampal neurons, and acute effects on fast excitatory neurotransmission were assessed. We found neurotransmission unaltered with respect to basal release probability, Ca2+ dependence of release, short-term plasticity, and fusion pore kinetics. In contrast, expression of a mutant Syt I with diminished Ca2+ affinity (R233Q) reduced release probability and altered the Ca2+ dependence of release, thus demonstrating the sensitivity of the system to changes in neurotransmission resulting from changes to the Ca2+ sensor. Together, these data refute the dominant model that Syt IV functions as an inhibitor of neurotransmitter release in mammalian neurons.
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Affiliation(s)
- Jonathan T Ting
- Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195, USA
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168
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Photowala H, Blackmer T, Schwartz E, Hamm HE, Alford S. G protein betagamma-subunits activated by serotonin mediate presynaptic inhibition by regulating vesicle fusion properties. Proc Natl Acad Sci U S A 2006; 103:4281-6. [PMID: 16537522 PMCID: PMC1449684 DOI: 10.1073/pnas.0600509103] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Neurotransmitters are thought to be released as quanta, where synaptic vesicles deliver packets of neurotransmitter to the synaptic cleft by fusion with the plasma membrane. However, synaptic vesicles may undergo incomplete fusion. We provide evidence that G protein-coupled receptors inhibit release by causing such incomplete fusion. 5-hydroxytryptamine (5-HT) receptor signaling potently inhibits excitatory postsynaptic currents (EPSCs) between lamprey reticulospinal axons and their postsynaptic targets by a direct action on the vesicle fusion machinery. We show that 5-HT receptor-mediated presynaptic inhibition, at this synapse, involves a reduction in EPSC quantal size. Quantal size was measured directly by comparing unitary quantal amplitudes of paired EPSCs before and during 5-HT application and indirectly by determining the effect of 5-HT on the relationship between mean-evoked EPSC amplitude and variance. Results from FM dye-labeling experiments indicate that 5-HT prevents full fusion of vesicles. 5-HT reduces FM1-43 staining of vesicles with a similar efficacy to its effect on the EPSC. However, destaining of FM1-43-labeled vesicles is abolished by lower concentrations of 5-HT that leave a substantial EPSC. The use of a water-soluble membrane impermeant quenching agent in the extracellular space reduced FM1-43 fluorescence during stimulation in 5-HT. Thus vesicles contact the extracellular space during inhibition of synaptic transmission by 5-HT. We conclude that 5-HT, via free Gbetagamma, prevents the collapse of synaptic vesicles into the presynaptic membrane.
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Affiliation(s)
- Huzefa Photowala
- *Department of Biological Sciences, University of Illinois, 840 West Taylor Street, Chicago, IL 60607; and
| | - Trillium Blackmer
- *Department of Biological Sciences, University of Illinois, 840 West Taylor Street, Chicago, IL 60607; and
| | - Eric Schwartz
- *Department of Biological Sciences, University of Illinois, 840 West Taylor Street, Chicago, IL 60607; and
| | - Heidi E. Hamm
- Department of Pharmacology, Vanderbilt University Medical School, 23rd Avenue South at Pierce, Nashville, TN 37232
| | - Simon Alford
- *Department of Biological Sciences, University of Illinois, 840 West Taylor Street, Chicago, IL 60607; and
- To whom correspondence should be addressed. E-mail:
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169
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Harata NC, Choi S, Pyle JL, Aravanis AM, Tsien RW. Frequency-dependent kinetics and prevalence of kiss-and-run and reuse at hippocampal synapses studied with novel quenching methods. Neuron 2006; 49:243-56. [PMID: 16423698 DOI: 10.1016/j.neuron.2005.12.018] [Citation(s) in RCA: 133] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/06/2005] [Revised: 10/12/2005] [Accepted: 12/21/2005] [Indexed: 11/29/2022]
Abstract
The kinetics of exo-endocytotic recycling could restrict information transfer at central synapses if neurotransmission were entirely reliant on classical full-collapse fusion. Nonclassical fusion retrieval by kiss-and-run would be kinetically advantageous but remains controversial. We used a hydrophilic quencher, bromophenol blue (BPB), to help detect nonclassical events. Upon stimulation, extracellular BPB entered synaptic vesicles and quenched FM1-43 fluorescence, indicating retention of FM dye beyond first fusion. BPB also quenched fluorescence of VAMP (synaptobrevin-2)-EGFP, thus indicating the timing of first fusion of vesicles in the total recycling pool. Comparison with FM dye destaining revealed that kiss-and-run strongly prevailed over full-collapse fusion at low frequency, giving way to a near-even balance at high frequency. Quickening of kiss-and-run vesicle reuse was also observed at higher frequency in the average single vesicle fluorescence response. Kiss-and-run and reuse could enable hippocampal nerve terminals to conserve scarce vesicular resources when responding to widely varying input patterns.
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Affiliation(s)
- Nobutoshi C Harata
- Department of Molecular and Cellular Physiology, Stanford University School of Medicine, Stanford, California 94305, USA
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170
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Nolan S, Cowan AE, Koppel DE, Jin H, Grote E. FUS1 regulates the opening and expansion of fusion pores between mating yeast. Mol Biol Cell 2006; 17:2439-50. [PMID: 16495338 PMCID: PMC1446097 DOI: 10.1091/mbc.e05-11-1015] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Mating yeast cells provide a genetically accessible system for the study of cell fusion. The dynamics of fusion pores between yeast cells were analyzed by following the exchange of fluorescent markers between fusion partners. Upon plasma membrane fusion, cytoplasmic GFP and DsRed diffuse between cells at rates proportional to the size of the fusion pore. GFP permeance measurements reveal that a typical fusion pore opens with a burst and then gradually expands. In some mating pairs, a sudden increase in GFP permeance was found, consistent with the opening of a second pore. In contrast, other fusion pores closed after permitting a limited amount of cytoplasmic exchange. Deletion of FUS1 from both mating partners caused a >10-fold reduction in the initial permeance and expansion rate of the fusion pore. Although fus1 mating pairs also have a defect in degrading the cell wall that separates mating partners before plasma membrane fusion, other cell fusion mutants with cell wall remodeling defects had more modest effects on fusion pore permeance. Karyogamy is delayed by >1 h in fus1 mating pairs, possibly as a consequence of retarded fusion pore expansion.
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Affiliation(s)
- Scott Nolan
- Department of Biochemistry and Molecular Biology, Johns Hopkins Bloomberg School of Public Health, Baltimore, MD 21205, USA
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171
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Fulop T, Radabaugh S, Smith C. Activity-dependent differential transmitter release in mouse adrenal chromaffin cells. J Neurosci 2006; 25:7324-32. [PMID: 16093382 PMCID: PMC6725304 DOI: 10.1523/jneurosci.2042-05.2005] [Citation(s) in RCA: 176] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Chromaffin cells of the adrenal medulla are a primary neuroendocrine output of the sympathetic nervous system. When stimulated, they secrete a host of transmitter molecules, including catecholamines and neuropeptides, through the fusion of dense core secretory granules with the cell surface. At basal firing rates, set by the sympathetic tone, chromaffin cells selectively release catecholamines at a modest rate. Stress-mediated sympathetic activation leads to elevated catecholamine secretion and also evokes neuropeptide release. Catecholamines and neuropeptides are copackaged in the same granules; thus, it is unclear how this activity-dependent differential transmitter release is achieved. In this report, we use electrophysiological, electrochemical, fluorescence, and immunocytochemical approaches to quantify transmitter release under physiological electrical stimulation at the single cell level. We provide data to show that chromaffin cells selectively release catecholamine under basal firing conditions but release both neuropeptides and catecholamines under conditions that match acute stress. We further show that this differential transmitter release is achieved through a regulated activity-dependent dilation of the granule fusion pore. Thus, chromaffin cells may regulate release of different transmitters through a simple size-exclusion mechanism.
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Affiliation(s)
- Tiberiu Fulop
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, Ohio 44106-4970, USA
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172
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Sokac AM, Bement WM. Kiss-and-coat and compartment mixing: coupling exocytosis to signal generation and local actin assembly. Mol Biol Cell 2006; 17:1495-502. [PMID: 16436510 PMCID: PMC1415325 DOI: 10.1091/mbc.e05-10-0908] [Citation(s) in RCA: 67] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Regulated exocytosis is thought to occur either by "full fusion," where the secretory vesicle fuses with the plasma membrane (PM) via a fusion pore that then dilates until the secretory vesicle collapses into the PM; or by "kiss-and-run," where the fusion pore does not dilate and instead rapidly reseals such that the secretory vesicle is retrieved almost fully intact. Here, we describe growing evidence for a third form of exocytosis, dubbed "kiss-and-coat," which is characteristic of a broad variety of cell types that undergo regulated exocytosis. Kiss-and-coat exocytosis entails prolonged maintenance of a dilated fusion pore and assembly of actin filament (F-actin) coats around the exocytosing secretory vesicles followed by direct retrieval of some fraction of the emptied vesicle membrane. We propose that assembly of the actin coats results from the union of the secretory vesicle membrane and PM and that this compartment mixing represents a general mechanism for generating local signals via directed membrane fusion.
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Affiliation(s)
- Anna M Sokac
- Department of Molecular Biology, Princeton University, Princeton, NJ 08544, USA
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173
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Dickman DK, Horne JA, Meinertzhagen IA, Schwarz TL. A slowed classical pathway rather than kiss-and-run mediates endocytosis at synapses lacking synaptojanin and endophilin. Cell 2005; 123:521-33. [PMID: 16269341 DOI: 10.1016/j.cell.2005.09.026] [Citation(s) in RCA: 155] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/21/2005] [Revised: 07/27/2005] [Accepted: 09/20/2005] [Indexed: 02/05/2023]
Abstract
The extent to which a "kiss-and-run" mode of endocytosis contributes to synaptic-vesicle recycling remains controversial. The only genetic evidence for kiss-and-run at the synapse comes from mutations in the genes encoding synaptojanin and endophilin, proteins that together function to uncoat vesicles in classical clathrin-mediated endocytosis. Here we have characterized the endocytosis that persists in null alleles of Drosophila synaptojanin and endophilin. In response to high-frequency stimulation, the synaptic-vesicle pool can be reversibly depleted in these mutants. Recovery from this depletion is slow and indicates the persistence of an impaired form of classical endocytosis. Steady-state exocytosis rates reveal that endocytosis saturates in mutant neuromuscular terminals at approximately 80 vesicles/s, 10%-20% of the wild-type rate. Analyses of quantal size, FM1-43 loading, and dynamin function further demonstrate that, even in the absence of synaptojanin or endophilin, vesicles undergo full fusion and re-formation. Therefore, no genetic evidence remains to indicate that synaptic vesicles undergo kiss-and-run.
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Affiliation(s)
- Dion K Dickman
- Division of Neuroscience, Children,s Hospital and Department of Neurobiology, Harvard Medical School, Boston, Massachusetts 02115, USA
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174
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MacDonald PE, Eliasson L, Rorsman P. Calcium increases endocytotic vesicle size and accelerates membrane fission in insulin-secreting INS-1 cells. J Cell Sci 2005; 118:5911-20. [PMID: 16317049 DOI: 10.1242/jcs.02685] [Citation(s) in RCA: 60] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
In many cells, endocytotic membrane retrieval is accelerated by Ca2+. The effect of Ca2+ on single endocytotic vesicles and fission pore kinetics was examined by measuring capacitance and conductance changes in small membrane patches of insulin-secreting INS-1 cells. In intact cells, elevation of Ca2+ by glucose stimulation induced a 1.8-fold increase in membrane internalisation. This surprisingly resulted from an increased unitary capacitance of endocytotic vesicles whereas the frequency of endocytosis was unaltered. This effect of glucose was prevented by inhibition of L- or R-type Ca2+ channels. Extracellular (pipette) Ca2+ was found to regulate endocytotic vesicle capacitance in a bimodal manner. Vesicle capacitance was increased at intermediate Ca2+ (2.6 mM), but not at high Ca2+ (10 mM). Similar results were obtained upon direct application of 100 nM and 0.5 mM Ca2+ to the intracellular surface of inside-out excised membrane patches, and in these experiments the increase in vesicle capacitance was prevented by the calcineurin inhibitor deltamethrin. Endocytotic fission pore kinetics were accelerated by Ca2+ in both the intact cells and isolated membrane patches; however, the effect in this case was neither bimodal nor deltamethrin sensitive. Membrane retrieval can therefore be upregulated by a Ca2+-dependent increase in endocytotic vesicle size and acceleration of membrane fission in insulin-secreting INS-1 cells.
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Affiliation(s)
- Patrick E MacDonald
- Division of Diabetes, Metabolism and Endocrinology, Lund University, 221 84 Lund, Sweden.
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175
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Abstract
Compound exocytosis occurs in many cell types. It represents a specialized form of secretion in which vesicles undergo fusion with each other as well as with the plasma membrane. In most cases, compound exocytosis occurs sequentially, with deeper-lying vesicles fusing, after a delay, with vesicles that have already fused with the plasma membrane. However, in some cells, vesicles can also apparently fuse with each other intracellularly before any interaction with the plasma membrane. In this review, we discuss the general features of compound exocytosis, and the features that are specific to particular cells. We consider mechanisms that might impose the requirement for vesicles to fuse with the plasma membrane before they become able to fuse with each other, the possibility that there are biochemical differences between vesicle-plasma membrane fusion events and subsequent secondary homotypic vesicle fusion events, and the role that cytoskeletal elements might play in the stabilization of fused vesicles, in order to permit secondary fusion events. Finally, we discuss the likely physiological significance of compound exocytosis in the various cell types in which it exists.
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Affiliation(s)
- James A Pickett
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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176
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Liu TT, Kishimoto T, Hatakeyama H, Nemoto T, Takahashi N, Kasai H. Exocytosis and endocytosis of small vesicles in PC12 cells studied with TEPIQ (two-photon extracellular polar-tracer imaging-based quantification) analysis. J Physiol 2005; 568:917-29. [PMID: 16150796 PMCID: PMC1464175 DOI: 10.1113/jphysiol.2005.094011] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2005] [Accepted: 09/01/2005] [Indexed: 11/08/2022] Open
Abstract
We investigated exocytosis of PC12 cells using two-photon excitation imaging and extracellular polar tracers (TEP imaging) in the lateral membranes not facing the glass-cover slip. Upon photolysis of a caged Ca2+ compound, TEP imaging with FM1-43 (a polar membrane tracer) detected massive exocytosis of vesicles with a time constant of about 1 s. TEPIQ (two-photon extracellular polar-tracer imaging-based quantification) analysis revealed that the diameter of vesicles was small (55 nm). Extensive exocytosis of small vesicles (SVs) was shown to be mediated by the transient opening of a fusion pore with a diameter less than about 1.6 nm, and to be followed by direct ('kiss-and-run') endocytosis and translocation of the endocytic vesicles (EVs) deep into the cytoplasm. These processes were unaffected by GTP-gamma-S. In contrast, constitutive endocytic vesicles exhibited a diameter of 90 nm, took up molecules with a diameter of > 12 nm, and their formation was blocked by GTP-gamma-S. Electron-microscopic investigation with photoconversion of diaminobenzidine using FM1-43 confirmed an abundance of EVs with a diameter of 54 nm in stimulated cells. They rapidly translocated into the cytosol, and fused with endosomal organelles. The number of SV exocytosis events vastly exceeded the number of SVs morphologically docked at the plasma membrane. Simultaneous capacitance and FM1-43 measurements indicated that TEP imaging detected most SV exocytosis, and the fusion pore was closed within 2 s. Thus, we have, for the first time, directly visualized massive exocytosis of small vesicles in a non-synaptic preparation, and have revealed their fusion-pore mediated exocytosis and endocytosis.
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Affiliation(s)
- Ting-Ting Liu
- Department of Cell Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan
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177
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Giraudo CG, Hu C, You D, Slovic AM, Mosharov EV, Sulzer D, Melia TJ, Rothman JE. SNAREs can promote complete fusion and hemifusion as alternative outcomes. ACTA ACUST UNITED AC 2005; 170:249-60. [PMID: 16027221 PMCID: PMC2171417 DOI: 10.1083/jcb.200501093] [Citation(s) in RCA: 110] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Using a cell fusion assay, we show here that in addition to complete fusion SNAREs also promote hemifusion as an alternative outcome. Approximately 65% of events resulted in full fusion, and the remaining 35% in hemifusion; of those, approximately two thirds were permanent and approximately one third were reversible. We predict that this relatively close balance among outcomes could be tipped by binding of regulatory proteins to the SNAREs, allowing for dynamic physiological regulation between full fusion and reversible kiss-and-run–like events.
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Affiliation(s)
- Claudio G Giraudo
- Department of Physiology and Cellular Biophysics, Columbia University College of Physicians and Surgeons, New York, NY 10032, USA
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178
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Dernick G, Gong LW, Tabares L, Alvarez de Toledo G, Lindau M. Patch amperometry: high-resolution measurements of single-vesicle fusion and release. Nat Methods 2005; 2:699-708. [PMID: 16118641 DOI: 10.1038/nmeth0905-699] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Affiliation(s)
- Gregor Dernick
- School of Applied and Engineering Physics, Cornell University, Ithaca, New York 14850, USA
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179
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Grabner CP, Price SD, Lysakowski A, Fox AP. Mouse chromaffin cells have two populations of dense core vesicles. J Neurophysiol 2005; 94:2093-104. [PMID: 15944233 DOI: 10.1152/jn.00316.2005] [Citation(s) in RCA: 76] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
The quantal hypothesis states that neurotransmitter is released in discrete packages, quanta, thought to represent the neurotransmitter content of individual vesicles. If true, then vesicle size should influence quantal size. Although chromaffin cells are generally thought to have a single population of secretory vesicles, our electron microscopy analysis suggested two populations as the size distribution was best described as the sum of two Gaussians. The average volume difference was fivefold. To test whether this difference in volume affected quantal size, neurotransmitter release from permeabilized cells exposed to 100 microM Ca2+ was measured with amperometry. Quantal content was bimodally distributed with both large and small events; the distribution of vesicle sizes predicted by amperometry was extremely similar to those measured with electron microscopy. In addition, each population of events exhibited distinct release kinetics. These results suggest that chromaffin cells have two populations of dense core vesicles (DCV) with unique secretory properties and which may represent two distinct synthetic pathways for DCV biogenesis or alternatively they may represent different stages of biosynthesis.
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Affiliation(s)
- Chad P Grabner
- Department of Neurobiology, Pharmacology, and Physiology, The University of Chicago, 947 E. 58 St., Chicago, Illinois 60637, USA.
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180
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Richards DA, Bai J, Chapman ER. Two modes of exocytosis at hippocampal synapses revealed by rate of FM1-43 efflux from individual vesicles. ACTA ACUST UNITED AC 2005; 168:929-39. [PMID: 15767463 PMCID: PMC2171786 DOI: 10.1083/jcb.200407148] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
We have examined the kinetics by which FM1-43 escapes from individual synaptic vesicles during exocytosis at hippocampal boutons. Two populations of exocytic events were observed; small amplitude events that lose dye slowly, which made up more than half of all events, and faster, larger amplitude events with a fluorescence intensity equivalent to single stained synaptic vesicles. These populations of destaining events are distinct in both brightness and kinetics, suggesting that they result from two distinct modes of exocytosis. Small amplitude events show tightly clustered rate constants of dye release, whereas larger events have a more scattered distribution. Kinetic analysis of the association and dissociation of FM1-43 with membranes, in combination with a simple pore permeation model, indicates that the small, slowly destaining events may be mediated by a narrow ∼1-nm fusion pore.
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Affiliation(s)
- David A Richards
- Department of Physiology, University of Wisconsin-Madison, Madison, WI 53706, USA
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181
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Li Z, Burrone J, Tyler WJ, Hartman KN, Albeanu DF, Murthy VN. Synaptic vesicle recycling studied in transgenic mice expressing synaptopHluorin. Proc Natl Acad Sci U S A 2005; 102:6131-6. [PMID: 15837917 PMCID: PMC1087931 DOI: 10.1073/pnas.0501145102] [Citation(s) in RCA: 124] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Synaptic vesicles are recycled locally within presynaptic specializations. We examined how vesicles are reused after endocytosis, using transgenic mice expressing the genetically encoded fluorescent indicator synaptopHluorin in subsets of neurons. At both excitatory and inhibitory synapses in cultured hippocampal neurons, newly endocytosed vesicles did not preferentially enter the releasable pool of vesicles. Rather, they entered the reserve pool first and subsequently the readily releasable pool over a period of several minutes. All vesicles in the recycling pool could be accessed by spaced stimuli, arguing against preferential local reuse of the readily releasable vesicles. Interestingly, nearly half the vesicles at excitatory synapses, and a third at inhibitory synapses, could not be recruited for release even by sustained stimuli. We conclude that, at presynaptic terminals in the hippocampus, most vesicles vacate release sites after exocytosis and are replaced by existing vesicles from the reserve pool, placing constraints on kiss-and-run recycling.
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Affiliation(s)
- Zhiying Li
- Department of Molecular and Cellular Biology, Harvard University, 16 Divinity Avenue, Cambridge, MA 02138, USA
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182
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Amatore C, Arbault S, Bonifas I, Bouret Y, Erard M, Ewing AG, Sombers LA. Correlation between vesicle quantal size and fusion pore release in chromaffin cell exocytosis. Biophys J 2005; 88:4411-20. [PMID: 15792983 PMCID: PMC1305668 DOI: 10.1529/biophysj.104.053736] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A significant number of exocytosis events recorded with amperometry demonstrate a prespike feature termed a "foot" and this foot has been correlated with messengers released via a transitory fusion pore before full exocytosis. We have compared amperometric spikes with a foot with spikes without a foot at chromaffin cells and found that the probability of detecting a distinct foot event is correlated to the amount of catecholamine released. The mean charge of the spikes with a foot was found to be twice that of the spikes without a foot, and the frequency of spikes displaying a foot was zero for small spikes increasing to approximately 50% for large spikes. It is hypothesized that in chromaffin cells, where the dense core is believed to nearly fill the vesicle, the expanding core is a controlling factor in opening the fusion pore, that prefusion of two smaller vesicles leads to excess membrane, and that this slows pore expansion leading to an increased observation of events with a foot. Clearly, the physicochemical properties of vesicles are key factors in the control of the dynamics of release through the fusion pore and the high and variable frequency of this release makes it highly significant.
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Affiliation(s)
- Christian Amatore
- Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640 PASTEUR, Paris, France.
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183
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Abstract
Neurons communicate with one another through the release of molecules from synaptic vesicles and large dense core granules through the process of exocytosis. During exocytosis, molecules are released to the extracellular space through a fusion pore, which can either dilate, resulting in full fusion, or close, resulting in incomplete exocytosis, often referred to as 'kiss and run' exocytosis. Recently, there has been much interest in the regulation of this process in both neurons and neuroendocrine cells. There has been much recent work that addresses the existence of incomplete exocytosis in neurons and neuroendocrine cells, as well as recent work probing the molecular components and modulation of the fusion pore.
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Affiliation(s)
- Seong An
- Yale University School of Medicine, Department of Cellular and Molecular Physiology, Sterling Hall of Medicine, B-147, 333 Cedar St, New Haven, Connecticut 06520, USA
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184
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MacDonald PE, Obermüller S, Vikman J, Galvanovskis J, Rorsman P, Eliasson L. Regulated exocytosis and kiss-and-run of synaptic-like microvesicles in INS-1 and primary rat beta-cells. Diabetes 2005; 54:736-43. [PMID: 15734850 DOI: 10.2337/diabetes.54.3.736] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022]
Abstract
We have applied cell-attached capacitance measurements to investigate whether synaptic-like microvesicles (SLMVs) undergo regulated exocytosis in insulinoma and primary pancreatic beta-cells. SLMV and large dense-core vesicle (LDCV) exocytosis was increased 1.6- and 2.4-fold upon stimulation with 10 mmol/l glucose in INS-1 cells. Exocytosis of both types of vesicles was coupled to Ca(2+) entry through l-type channels. Thirty percent of SLMV exocytosis in INS-1 and rat beta-cells was associated with transient capacitance increases consistent with kiss-and-run. Elevation of intracellular cAMP (5 micromol/l forskolin) increased SLMV exocytosis 1.6-fold and lengthened the duration of kiss-and-run events in rat beta-cells. Experiments using isolated inside-out patches of INS-1 cells revealed that the readily releasable pool (RRP) of SLMVs preferentially undergoes kiss-and-run exocytosis (67%), is proportionally larger than the LDCV RRP, and is depleted more quickly upon Ca(2+) stimulation. We conclude that SLMVs undergo glucose-regulated exocytosis and are capable of high turnover. Following kiss-and-run exocytosis, the SLMV RRP may be reloaded with gamma-aminobutyric acid and undergo several cycles of exo- and endocytosis. Our observations support a role for beta-cell SLMVs in a synaptic-like function of rapid intra-islet signaling.
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Affiliation(s)
- Patrick E MacDonald
- Section of Diabetes, Metabolism and Endocrinology, Lund University, Lund, Sweden.
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185
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Kebir S, Aristizabal F, Maysinger D, Glavinović MI. Rapid change of quantal size in PC-12 cells detected by neural networks. J Neurosci Methods 2005; 142:231-42. [PMID: 15698663 DOI: 10.1016/j.jneumeth.2004.08.014] [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] [Received: 05/05/2004] [Revised: 08/12/2004] [Accepted: 08/19/2004] [Indexed: 11/17/2022]
Abstract
The basic building block of synaptic transmission-the number of molecules released per vesicle (quantal size (QS)) often changes with stimulation, but there is no agreement about what factors regulate it. To throw more light on this problem spontaneous quantal release was recorded amperometrically in PC-12 cells. Amperometric current spikes, representing single vesicle release, were detected by thresholding and were separated from spurious events on the basis of their amplitude and time course using a pattern recognition system based on the principal component neural network methods. The frequency of current spikes, their amplitude, quantal size, rise time and decay time were typically non-stationary, even in the absence of stimulation. Their running values changed much more than those of memoryless stationary random data with the same probability density distribution. Irrespective of how much the quantal size, rise and decay times varied, their amplitude dependence remained constant, or changed with a very different time course. In conclusion, the quantal size is highly labile in PC-12 cells. The lability does not appear to result from the changes of fusion pore dynamics or the mechanism of release of vesicular content, but because of the preferential release of large vesicles.
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Affiliation(s)
- S Kebir
- Department of Physiology, McGill University, Montreal, Canada
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186
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Abstract
Communication between cells reaches its highest degree of specialization at chemical synapses. Some synapses talk in a 'whisper'; others 'shout'. The 'louder' the synapse, the more synaptic vesicles are needed to maintain effective transmission, ranging from a few hundred (whisperers) to nearly a million (shouters). These vesicles reside in different 'pools', which have been given a bewildering array of names. In this review, we focus on five tissue preparations in which synaptic vesicle pools have been identified and thoroughly characterized. We argue that, in each preparation, each vesicle can be assigned to one of three distinct pools.
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Affiliation(s)
- Silvio O Rizzoli
- Max-Planck-Institut für biophysikalische Chemie, Göttingen, Germany
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187
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Santos-Sacchi J. Determination of cell capacitance using the exact empirical solution of partial differential Y/partial differential Cm and its phase angle. Biophys J 2005; 87:714-27. [PMID: 15240504 PMCID: PMC1304394 DOI: 10.1529/biophysj.103.033993] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Measures of membrane capacitance offer insight into a variety of cellular processes. Unfortunately, popular methodologies rely on model simplifications that sensitize them to interference from inevitable changes in resistive components of the traditional cell-clamp model. Here I report on a novel method to measure membrane capacitance that disposes of the usual simplifications and assumptions, yet is immune to such interference and works on the millisecond timescale. It is based on the exact empirical determination of the elusive partial derivative, partial differential Y/partial differential C(m), which heretofore had been approximated. Furthermore, I illustrate how this method extends to the vesicle fusion problem by permitting the determination of partial differential Y(v)/partial differential C(v), thereby providing estimates of fusion pore conductance and vesicle capacitance. Finally, I provide simulation examples and physiological examples of how the method can be used to study processes that are routinely interrogated by measures of membrane capacitance.
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Affiliation(s)
- Joseph Santos-Sacchi
- Otolaryngology and Neurobiology, Yale University School of Medicine, New Haven, Connecticut 06510, USA.
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188
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Pickett JA, Thorn P, Edwardson JM. The Plasma Membrane Q-SNARE Syntaxin 2 Enters the Zymogen Granule Membrane during Exocytosis in the Pancreatic Acinar Cell. J Biol Chem 2005; 280:1506-11. [PMID: 15536072 DOI: 10.1074/jbc.m411967200] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During exocytosis in the pancreatic acinar cell, zymogen granules fuse directly with the apical plasma membrane and also with granules that have themselves fused with the plasma membrane. Together, these primary and secondary fusion events constitute the process of compound exocytosis. It has been suggested that the sequential nature of primary and secondary fusion is a consequence of the requirement for plasma membrane soluble N-ethylmaleimide-sensitive fusion protein attachment protein receptors, such as syntaxin 2, to enter the membrane of the primary fused granule. We have tested this possibility by determining the location of syntaxin 2 in unstimulated and stimulated pancreatic acini. Syntaxin 2 was imaged by confocal immunofluorescence microscopy. Fused granules were detected both through their filling with the aqueous dye lysine-fixable Texas Red-dextran and through the decoration of their cytoplasmic surfaces with filamentous actin. In unstimulated cells, syntaxin 2 was exclusively present on the apical plasma membrane. In contrast, after stimulation, syntaxin 2 had moved into the membranes of fused granules, as judged by its location around dye-filled structures of 1-mum diameter that were coated with filamentous actin. At long times of stimulation (5 min), the majority (85%) of dye-filled granules were also positive for syntaxin 2. In contrast, at shorter times (1 min), more dye-filled granules (29%) were syntaxin 2-negative. We conclude that syntaxin 2 enters the membrane of a fused zymogen granule after the opening of the fusion pore, and we suggest that this movement might permit the onset of secondary fusion.
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Affiliation(s)
- James A Pickett
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, United Kingdom
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189
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Han X, Jackson MB. Response to Comment on "Transmembrane Segments of Syntaxin Line the Fusion Pore of Ca
2+
-Triggered Exocytosis". Science 2004. [DOI: 10.1126/science.1102272] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Affiliation(s)
- Xue Han
- Department of Physiology, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA
| | - Meyer B. Jackson
- Department of Physiology, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA
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190
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Edmonds BW, Gregory FD, Schweizer FE. Evidence that fast exocytosis can be predominantly mediated by vesicles not docked at active zones in frog saccular hair cells. J Physiol 2004; 560:439-50. [PMID: 15308677 PMCID: PMC1665261 DOI: 10.1113/jphysiol.2004.066035] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
The prevailing model of neurotransmitter release stipulates that Ca2+ influx triggers the rapid fusion of vesicles that are docked at presynaptic active zones. Under this model, slower tonic release is supported by vesicles clustered nearby that have to translocate to the release sites before fusion. We have examined this hypothesis at the afferent synapse of saccular hair cells of the leopard frog, Rana pipiens. Detailed morphological measurements at this ribbon synapse show that on average 32 vesicles are docked at each active zone. We show that at this 'graded' synapse, depolarization produces an exocytotic 'burst' that is largely complete within 20 ms after fusion of 280 vesicles per active zone, almost an order of magnitude more than expected. Recovery from paired pulse depression occurs with a time constant of 29 ms, indicating that replenishment of this fast-fusing pool of vesicles is also fast. Our results suggest that non-docked vesicles are capable of fast fusion and that these vesicles constitute the vast majority of the fast-fusing pool. The view that the population of fast-fusing presynaptic vesicles is limited to docked vesicles therefore requires re-evaluation. We propose that compound fusion, i.e. the fusion of vesicles with each other before and/or after they fuse with the membrane can explain multivesicular release at this synapse.
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Affiliation(s)
- Brian W Edmonds
- Department of Neurobiology, David Geffen School of Medicine at UCLA, University of California, Los Angeles, 650 Charles E. Young Drive South, Los Angeles, CA 90095, USA
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191
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Fisher JL, Levitan I, Margulies SS. Plasma Membrane Surface Increases with Tonic Stretch of Alveolar Epithelial Cells. Am J Respir Cell Mol Biol 2004; 31:200-8. [PMID: 15016618 DOI: 10.1165/rcmb.2003-0224oc] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Cyclic stretch stimulates numerous responses in alveolar epithelial cells--some beneficial, some injurious--often through mechanosensitive membrane-associated proteins such as stretch-activated ion channels. Tonic stretch, in contrast, stimulates only some of these responses. In this study, we hypothesized that the plasma membranes of alveolar epithelial cells expand during tonic stretch, not only through cell surface unfolding, but also through recruitment of additional phospholipids. Such plasma membrane expansion would reduce membrane tension and decrease stimulation of mechanosensitive membrane proteins. Primary rat alveolar epithelial cells were isolated, cultured for 48 h, and stretched between 3 and 40% change in basal membrane surface area. Gross changes in total cell surface area were obtained from stacks of thin fluorescent confocal micrographs; fine changes in plasma membrane area were measured via whole cell capacitance. A 1:1 correspondence linked changes in basal and total cell surface area, implying that cell surface area change is dominated by stretch of the attached basal surface. We also found that plasma membrane increased proportionally with surface area within 5 min of tonic stretch, showing that, given time to occur, plasma membrane expansion via lipid recruitment preponderates the changes in cell surface shape and size demanded by stretching the cell. Similarly, in cells tonically stretched 10 min to allow lipid insertion and then returned to an unstretched state, reabsorption of excess lipid occurred within 5 min. Finally, we found that lipid insertion induced by tonic stretch was unaffected by F-actin disassembly, ATP depletion, and calcium deprivation.
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Affiliation(s)
- Jacob L Fisher
- Department of Bioengineering, University of Pennsylvania, 3320 Smith Walk, Philadelphia, PA 19104-6392, USA
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192
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Abstract
How synapses change their strength in response to impinging neural activity is a fundamental issue for understanding how the brain molds its circuitry in response to behavioral experience. Although a growing number of studies reveal the involvement of postsynaptic changes contributing to synaptic plasticity in brain circuits, the involvement of presynaptic factors has been implied by several studies. Most recently, several works point to the mechanism of vesicle fusion as a new possible locus for the modification of presynaptic synaptic strength. However, it is not yet clear to what extent such changes affect the simplest form of information transfer in the brain--the transmission of a single action potential.
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Affiliation(s)
- Boris Krupa
- Picower Center for Learning and Memory, RIKEN-MIT Neuroscience Research Center, Department of Brain and Cognitive Sciences, MIT, Cambridge, MA 02139, USA
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193
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Zhang C, Xiong W, Zheng H, Wang L, Lu B, Zhou Z. Calcium- and dynamin-independent endocytosis in dorsal root ganglion neurons. Neuron 2004; 42:225-36. [PMID: 15091339 DOI: 10.1016/s0896-6273(04)00189-8] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Revised: 01/12/2004] [Accepted: 03/10/2004] [Indexed: 10/26/2022]
Abstract
Synaptic vesicle endocytosis is believed to require calcium and the GTPase dynamin. We now report a form of rapid endocytosis (RE) in dorsal root ganglion (DRG) neurons that, unlike previously described forms of endocytosis, is independent of calcium and dynamin. The RE is tightly coupled to calcium-independent but voltage-dependent secretion (CIVDS). Using FM dye and capacitance measurements, we show that membrane depolarization induces RE in the absence of calcium. Inhibition of dynamin function does not affect RE. The magnitude of RE is proportional to that of preceding CIVDS and stimulation frequency. Inhibitors of protein kinase A (PKA) suppress RE induced by high-frequency depolarization, while PKA activators enhance RE induced by low-frequency depolarization. Biochemical experiments demonstrate that depolarization directly upregulates PKA activity in calcium-free medium. These results reveal a calcium- and dynamin-independent form of endocytosis, which is controlled by neuronal activity and PKA-dependent phosphorylation, in DRG neurons.
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Affiliation(s)
- Chen Zhang
- Institute of Neuroscience, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences, Shanghai 200031, China
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194
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Abstract
During exocytosis, the lumen of secretory vesicles connects with the extracellular space. In some vesicles, this connection closes again, causing the vesicle to be recaptured mostly intact. The degree to which the bilayers of such vesicles mix with the plasma membrane is unknown. Work supporting the kiss-and-run model of transient exocytosis implies that synaptic vesicles allow neither lipid nor protein to escape into the plasma membrane, suggesting that the two bilayers never merge. Here, we test whether neuroendocrine granules behave similarly. Using two-color evanescent field microscopy, we imaged the lipid probe FM4-64 and fluorescent proteins in single dense core granules. During exocytosis, granules lost FM4-64 into the plasma membrane in small fractions of a second. Although FM4-64 was lost, granules retained the membrane protein, GFP-phogrin. By using GFP-phogrin as a probe for resealing, it was found that even granules that reseal lose FM4-64. We conclude that the lipid bilayers of the granule and the plasma membrane become continuous even when exocytosis is transient.
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Affiliation(s)
- Justin W Taraska
- Vollum Institute, Oregon Health and Sciences University, 3181 Southwest Sam Jackson Park Road, Portland, OR 97239, USA
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195
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Nielsen TA, DiGregorio DA, Silver RA. Modulation of Glutamate Mobility Reveals the Mechanism Underlying Slow-Rising AMPAR EPSCs and the Diffusion Coefficient in the Synaptic Cleft. Neuron 2004; 42:757-71. [PMID: 15182716 DOI: 10.1016/j.neuron.2004.04.003] [Citation(s) in RCA: 174] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2003] [Revised: 03/19/2004] [Accepted: 04/28/2004] [Indexed: 11/16/2022]
Abstract
Fast- and slow-rising AMPA receptor-mediated EPSCs occur at central synapses. Fast-rising EPSCs are thought to be mediated by rapid local release of glutamate. However, two controversial mechanisms have been proposed to underlie slow-rising EPSCs: prolonged local release of transmitter via a fusion pore, and spillover of transmitter released rapidly from distant sites. We have investigated the mechanism underlying slow-rising EPSCs and the diffusion coefficient of glutamate in the synaptic cleft (Dglut) at cerebellar mossy fiber-granule cell synapses using a combination of diffusion modeling and patch-clamp recording. Simulations show that modulating Dglut has different effects on the peak amplitudes and time courses of EPSCs mediated by these two mechanisms. Slowing diffusion with the macromolecule dextran slowed slow-rising EPSCs and had little effect on their amplitude, indicating that glutamate spillover underlies these currents. Our results also suggest that under control conditions Dglut is approximately 3-fold lower than in free solution.
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Affiliation(s)
- Thomas A Nielsen
- Department of Physiology, University College London, Gower Street, London WC1E 6BT, United Kingdom
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196
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Fernández-Alfonso T, Ryan TA. The kinetics of synaptic vesicle pool depletion at CNS synaptic terminals. Neuron 2004; 41:943-53. [PMID: 15046726 DOI: 10.1016/s0896-6273(04)00113-8] [Citation(s) in RCA: 187] [Impact Index Per Article: 9.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2003] [Revised: 02/02/2004] [Accepted: 02/13/2004] [Indexed: 11/19/2022]
Abstract
During sustained action potential (AP) firing at nerve terminals, the rates of endocytosis compared to exocytosis determine how quickly the available synaptic vesicle pool is depleted, in turn influencing presynaptic efficacy. Mechanisms, including rapid kiss-and-run endocytosis as well as local, preferential recycling of docked vesicles, have been proposed as a means to allow endocytosis and recycling to keep up with stimulation. We show here that, for CNS nerve terminals at physiological temperatures, endocytosis is sufficiently fast to avoid vesicle pool depletion during continuous AP firing at 10 Hz. This endocytosis-exocytosis balance persists for turnover of the entire releasable pool of vesicles and allows for efficient escape of FM 4-64, indicating that it is a non-kiss-and-run endocytic event. Thus, under physiological conditions, the sustained speed of vesicle membrane retrieval for the entire releasable pool appears to be sufficiently fast to compensate for exocytosis, avoiding significant vesicle pool depletion during robust synaptic activity.
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Affiliation(s)
- Tomás Fernández-Alfonso
- Department of Biochemistry, The Weill Medical College of Cornell University, New York, NY 10021, USA
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197
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Pawlu C, DiAntonio A, Heckmann M. Postfusional Control of Quantal Current Shape. Neuron 2004; 42:607-18. [PMID: 15157422 DOI: 10.1016/s0896-6273(04)00269-7] [Citation(s) in RCA: 94] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2002] [Revised: 02/17/2004] [Accepted: 04/05/2004] [Indexed: 11/18/2022]
Abstract
Whether glutamate is released rapidly, in an all-or-none manner, or more slowly, in a regulated manner, is a matter of debate. We analyzed the time course of excitatory postsynaptic currents (EPSCs) at glutamatergic neuromuscular junctions of Drosophila and found that the decay phase of EPSCs was protracted to a variable extent. The protraction was more pronounced in evoked and spontaneous quantal EPSCs than in action potential-evoked multiquantal EPSCs; reduced in quantal EPSCs from endophilin null mutants, which maintain release via kiss-and-run; and dependent on synaptotagmin isoform, calcium, and protein phosphorylation. Our data indicate that glutamate is released from individual synaptic vesicles for milliseconds through a fusion pore. Quantal glutamate discharge time course depends on presynaptic calcium inflow and the molecular composition of the release machinery.
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Affiliation(s)
- Christian Pawlu
- Physiologisches Institut, Universität Freiburg, D-79104 Freiburg, Germany
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198
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Heifetz Y, Wolfner MF. Mating, seminal fluid components, and sperm cause changes in vesicle release in the Drosophila female reproductive tract. Proc Natl Acad Sci U S A 2004; 101:6261-6. [PMID: 15071179 PMCID: PMC395957 DOI: 10.1073/pnas.0401337101] [Citation(s) in RCA: 72] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/22/2003] [Indexed: 11/18/2022] Open
Abstract
Mating induces changes in female insects, including in egg production, ovulation and laying, sperm storage, and behavior. Several molecules and effects that induce these changes have been identified, but their proximate effects on females remain unexplored. We examined whether vesicle release occurs as a consequence of mating; we used transgenic Drosophila that allow monitoring of secretory granule release at nerve termini. Changes in release occur at specific times postmating in different regions of the female reproductive tract: soon after mating in the lower reproductive tract, and later in the upper reproductive tract. Some changes are triggered by receipt of sperm, others by male seminal proteins, and still others by the act of mating itself (or other unidentified effectors). Our findings indicate that the female reproductive tract is a multi-organ system whose regions are modulated separately by mating and mating components. This modulation could create an environment conducive to increased reproductive capacity.
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Affiliation(s)
- Yael Heifetz
- Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14853, USA
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199
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200
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Han X, Wang CT, Bai J, Chapman ER, Jackson MB. Transmembrane segments of syntaxin line the fusion pore of Ca2+-triggered exocytosis. Science 2004; 304:289-92. [PMID: 15016962 DOI: 10.1126/science.1095801] [Citation(s) in RCA: 247] [Impact Index Per Article: 12.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/02/2022]
Abstract
The fusion pore of regulated exocytosis is a channel that connects and spans the vesicle and plasma membranes. The molecular composition of this important intermediate structure of exocytosis is unknown. Here, we found that mutations of some residues within the transmembrane segment of syntaxin (Syx), a plasma membrane protein essential for exocytosis, altered neurotransmitter flux through fusion pores and altered pore conductance. The residues that influenced fusion-pore flux lay along one face of an alpha-helical model. Thus, the fusion pore is formed at least in part by a circular arrangement of 5 to 8 Syx transmembrane segments in the plasma membrane.
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Affiliation(s)
- Xue Han
- Department of Physiology, University of Wisconsin, 1300 University Avenue, Madison, WI 53706, USA
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