1
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Yang L, Fomina AF. Ca 2+ influx and clearance at hyperpolarized membrane potentials modulate spontaneous and stimulated exocytosis in neuroendocrine cells. Cell Calcium 2020; 87:102184. [PMID: 32151786 DOI: 10.1016/j.ceca.2020.102184] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 02/10/2020] [Accepted: 02/21/2020] [Indexed: 01/09/2023]
Abstract
Neuroendocrine adrenal chromaffin cells release neurohormones catecholamines in response to Ca2+ entry via voltage-gated Ca2+ channels (VGCCs). Adrenal chromaffin cells also express non-voltage-gated channels, which may conduct Ca2+ at negative membrane potentials, whose role in regulation of exocytosis is poorly understood. We explored how modulation of Ca2+ influx at negative membrane potentials affects basal cytosolic Ca2+ concentration ([Ca2+]i) and exocytosis in metabolically intact voltage-clamped bovine adrenal chromaffin cells. We found that in these cells, Ca2+ entry at negative membrane potentials is balanced by Ca2+ extrusion by the Na+/Ca2+ exchanger and that this balance can be altered by membrane hyperpolarization or stimulation with an inflammatory hormone bradykinin. Membrane hyperpolarization or application of bradykinin augmented Ca2+-carrying current at negative membrane potentials, elevated basal [Ca2+]i, and facilitated synchronous exocytosis evoked by the small amounts of Ca2+ injected into the cell via VGCCs (up to 20 pC). Exocytotic responses evoked by the injections of the larger amounts of Ca2+ via VGCCs (> 20 pC) were suppressed by preceding hyperpolarization. In the absence of Ca2+ entry via VGCCs and Ca2+ extrusion via the Na+/Ca2+ exchanger, membrane hyperpolarization induced a significant elevation in [Ca2+]i and asynchronous exocytosis. Our results indicate that physiological interferences, such as membrane hyperpolarization and/or activation of non-voltage-gated Ca2+ channels, modulate basal [Ca2+]i and, consequently, segregation of exocytotic vesicles and their readiness to be released spontaneously and in response to Ca2+ entry via VGCCs. These mechanisms may play role in homeostatic plasticity of neuronal and endocrine cells.
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Affiliation(s)
- Lukun Yang
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, 95616, USA; Department of Anesthesiology, The 5th Affiliated Hospital of SUN YAT-SEN University, Zhuhai, 519000, China.
| | - Alla F Fomina
- Department of Physiology and Membrane Biology, University of California, Davis, Davis, CA, 95616, USA.
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2
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Gillis KD, Liu XA, Marcantoni A, Carabelli V. Electrochemical measurement of quantal exocytosis using microchips. Pflugers Arch 2017; 470:97-112. [PMID: 28866728 DOI: 10.1007/s00424-017-2063-2] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2017] [Revised: 08/21/2017] [Accepted: 08/23/2017] [Indexed: 01/30/2023]
Abstract
Carbon-fiber electrodes (CFEs) are the gold standard for quantifying the release of oxidizable neurotransmitters from single vesicles and single cells. Over the last 15 years, microfabricated devices have emerged as alternatives to CFEs that offer the possibility of higher throughput, subcellular spatial resolution of exocytosis, and integration with other techniques for probing exocytosis including microfluidic cell handling and solution exchange, optical imaging and stimulation, and electrophysiological recording and stimulation. Here we review progress in developing electrochemical electrode devices capable of resolving quantal exocytosis that are fabricated using photolithography.
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Affiliation(s)
- Kevin D Gillis
- Department of Bioengineering, University of Missouri, Columbia, MO, USA.
- Department of Medical Pharmacology and Physiology, University of Missouri, Columbia, MO, USA.
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA.
| | - Xin A Liu
- Dalton Cardiovascular Research Center, University of Missouri, Columbia, MO, USA
| | - Andrea Marcantoni
- Department of Drug Science and "NIS" Inter-departmental Centre, University of Torino, Torino, Italy
| | - Valentina Carabelli
- Department of Drug Science and "NIS" Inter-departmental Centre, University of Torino, Torino, Italy
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3
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Chang CW, Chiang CW, Jackson MB. Fusion pores and their control of neurotransmitter and hormone release. J Gen Physiol 2017; 149:301-322. [PMID: 28167663 PMCID: PMC5339513 DOI: 10.1085/jgp.201611724] [Citation(s) in RCA: 51] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2016] [Revised: 01/06/2017] [Accepted: 01/19/2017] [Indexed: 11/20/2022] Open
Abstract
Chang et al. review fusion pore structure and dynamics and discuss the implications for hormone and neurotransmitter release Ca2+-triggered exocytosis functions broadly in the secretion of chemical signals, enabling neurons to release neurotransmitters and endocrine cells to release hormones. The biological demands on this process can vary enormously. Although synapses often release neurotransmitter in a small fraction of a millisecond, hormone release can be orders of magnitude slower. Vesicles usually contain multiple signaling molecules that can be released selectively and conditionally. Cells are able to control the speed, concentration profile, and content selectivity of release by tuning and tailoring exocytosis to meet different biological demands. Much of this regulation depends on the fusion pore—the aqueous pathway by which molecules leave a vesicle and move out into the surrounding extracellular space. Studies of fusion pores have illuminated how cells regulate secretion. Furthermore, the formation and growth of fusion pores serve as a readout for the progress of exocytosis, thus revealing key kinetic stages that provide clues about the underlying mechanisms. Herein, we review the structure, composition, and dynamics of fusion pores and discuss the implications for molecular mechanisms as well as for the cellular regulation of neurotransmitter and hormone release.
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Affiliation(s)
- Che-Wei Chang
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705
| | - Chung-Wei Chiang
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705
| | - Meyer B Jackson
- Department of Neuroscience, University of Wisconsin-Madison, Madison, WI 53705
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4
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Extrapolating microdomain Ca(2+) dynamics using BK channels as a Ca(2+) sensor. Sci Rep 2016; 6:17343. [PMID: 26776352 PMCID: PMC4726033 DOI: 10.1038/srep17343] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/19/2014] [Accepted: 10/22/2015] [Indexed: 11/17/2022] Open
Abstract
Ca2+ ions play crucial roles in mediating physiological and pathophysiological processes, yet Ca2+ dynamics local to the Ca2+ source, either from influx via calcium permeable ion channels on plasmic membrane or release from internal Ca2+ stores, is difficult to delineate. Large-conductance calcium-activated K+ (BK-type) channels, abundantly distribute in excitable cells and often localize to the proximity of voltage-gated Ca2+ channels (VGCCs), spatially enabling the coupling of the intracellular Ca2+ signal to the channel gating to regulate membrane excitability and spike firing patterns. Here we utilized the sensitivity and dynamic range of BK to explore non-uniform Ca2+ local transients in the microdomain of VGCCs. Accordingly, we applied flash photolysis of caged Ca2+ to activate BK channels and determine their intrinsic sensitivity to Ca2+. We found that uncaging Ca2+ activated biphasic BK currents with fast and slow components (time constants being τf ≈ 0.2 ms and τs ≈ 10 ms), which can be accounted for by biphasic Ca2+ transients following light photolysis. We estimated the Ca2+-binding rate constant kb (≈1.8 × 108 M−1s−1) for mSlo1 and further developed a model in which BK channels act as a calcium sensor capable of quantitatively predicting local microdomain Ca2+ transients in the vicinity of VGCCs during action potentials.
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Lefkowitz JJ, DeCrescenzo V, Duan K, Bellve KD, Fogarty KE, Walsh JV, ZhuGe R. Catecholamine exocytosis during low frequency stimulation in mouse adrenal chromaffin cells is primarily asynchronous and controlled by the novel mechanism of Ca2+ syntilla suppression. J Physiol 2014; 592:4639-55. [PMID: 25128575 DOI: 10.1113/jphysiol.2014.278127] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Adrenal chromaffin cells (ACCs), stimulated by the splanchnic nerve, generate action potentials (APs) at a frequency near 0.5 Hz in the resting physiological state, at times described as 'rest and digest'. How such low frequency stimulation in turn elicits sufficient catecholamine exocytosis to set basal sympathetic tone is not readily explained by the classical mechanism of stimulus-secretion coupling, where exocytosis is synchronized to AP-induced Ca(2+) influx. By using simulated action potentials (sAPs) at 0.5 Hz in isolated patch-clamped mouse ACCs, we show here that less than 10% of all catecholaminergic exocytosis, measured by carbon fibre amperometry, is synchronized to an AP. The asynchronous phase, the dominant phase, of exocytosis does not require Ca(2+) influx. Furthermore, increased asynchronous exocytosis is accompanied by an AP-dependent decrease in frequency of Ca(2+) syntillas (i.e. transient, focal Ca(2+) release from internal stores) and is ryanodine sensitive. We propose a mechanism of disinhibition, wherein APs suppress Ca(2+) syntillas, which themselves inhibit exocytosis as they do in the case of spontaneous catecholaminergic exocytosis.
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Affiliation(s)
- Jason J Lefkowitz
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, 01655, USA
| | - Valerie DeCrescenzo
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, 01655, USA
| | - Kailai Duan
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, 01655, USA
| | - Karl D Bellve
- Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, MA, 01655, USA Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, 01655, USA
| | - Kevin E Fogarty
- Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, MA, 01655, USA Program in Molecular Medicine, University of Massachusetts Medical School, Worcester, MA, 01655, USA
| | - John V Walsh
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, 01655, USA Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, MA, 01655, USA
| | - Ronghua ZhuGe
- Department of Microbiology and Physiological Systems, University of Massachusetts Medical School, Worcester, MA, 01655, USA Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, MA, 01655, USA
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6
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Chiang N, Hsiao YT, Yang HJ, Lin YC, Lu JC, Wang CT. Phosphomimetic mutation of cysteine string protein-α increases the rate of regulated exocytosis by modulating fusion pore dynamics in PC12 cells. PLoS One 2014; 9:e99180. [PMID: 24956274 PMCID: PMC4067274 DOI: 10.1371/journal.pone.0099180] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2014] [Accepted: 05/12/2014] [Indexed: 11/20/2022] Open
Abstract
Background Cysteine string protein-α (CSPα) is a chaperone to ensure protein folding. Loss of CSPα function associates with many neurological diseases. However, its function in modulating regulated exocytosis remains elusive. Although cspα-knockouts exhibit impaired synaptic transmission, overexpression of CSPα in neuroendocrine cells inhibits secretion. These seemingly conflicting results lead to a hypothesis that CSPα may undergo a modification that switches its function in regulating neurotransmitter and hormone secretion. Previous studies implied that CSPα undergoes phosphorylation at Ser10 that may influence exocytosis by altering fusion pore dynamics. However, direct evidence is missing up to date. Methodology/Principal Findings Using amperometry, we investigated how phosphorylation at Ser10 of CSPα (CSPα-Ser10) modulates regulated exocytosis and if this modulation involves regulating a specific kinetic step of fusion pore dynamics. The real-time exocytosis of single vesicles was detected in PC12 cells overexpressing control vector, wild-type CSPα (WT), the CSPα phosphodeficient mutant (S10A), or the CSPα phosphomimetic mutants (S10D and S10E). The shapes of amperometric signals were used to distinguish the full-fusion events (i.e., prespike feet followed by spikes) and the kiss-and-run events (i.e., square-shaped flickers). We found that the secretion rate was significantly increased in cells overexpressing S10D or S10E compared to WT or S10A. Further analysis showed that overexpression of S10D or S10E prolonged fusion pore lifetime compared to WT or S10A. The fraction of kiss-and-run events was significantly lower but the frequency of full-fusion events was higher in cells overexpressing S10D or S10E compared to WT or S10A. Advanced kinetic analysis suggests that overexpression of S10D or S10E may stabilize open fusion pores mainly by inhibiting them from closing. Conclusions/Significance CSPα may modulate fusion pore dynamics in a phosphorylation-dependent manner. Therefore, through changing its phosphorylated state influenced by diverse cellular signalings, CSPα may have a great capacity to modulate the rate of regulated exocytosis.
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Affiliation(s)
- Ning Chiang
- Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan
- Department of Life Science, National Taiwan University, Taipei, Taiwan
- Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan
| | - Yu-Tien Hsiao
- Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan
| | - Hui-Ju Yang
- Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan
| | - Yu-Chun Lin
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan
| | - Juu-Chin Lu
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, Taiwan
- * E-mail: (C-TW); (J-CL)
| | - Chih-Tien Wang
- Institute of Molecular and Cellular Biology, National Taiwan University, Taipei, Taiwan
- Department of Life Science, National Taiwan University, Taipei, Taiwan
- Neurobiology and Cognitive Science Center, National Taiwan University, Taipei, Taiwan
- Genome and Systems Biology Degree Program, National Taiwan University, Taipei, Taiwan
- * E-mail: (C-TW); (J-CL)
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7
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Gosso S, Turturici M, Franchino C, Colombo E, Pasquarelli A, Carbone E, Carabelli V. Heterogeneous distribution of exocytotic microdomains in adrenal chromaffin cells resolved by high-density diamond ultra-microelectrode arrays. J Physiol 2014; 592:3215-30. [PMID: 24879870 DOI: 10.1113/jphysiol.2014.274951] [Citation(s) in RCA: 25] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Here we describe the ability of a high-density diamond microelectrode array targeted to resolve multi-site detection of fast exocytotic events from single cells. The array consists of nine boron-doped nanocrystalline diamond ultra-microelectrodes (9-Ch NCD-UMEA) radially distributed within a circular area of the dimensions of a single cell. The device can be operated in voltammetric or chronoamperometric configuration. Sensitivity to catecholamines, tested by dose-response calibrations, set the lowest detectable concentration of adrenaline to ∼5 μm. Catecholamine release from bovine or mouse chromaffin cells could be triggered by electrical stimulation or external KCl-enriched solutions. Spikes detected from the cell apex using carbon fibre microelectrodes showed an excellent correspondence with events measured at the bottom of the cell by the 9-Ch NCD-UMEA, confirming the ability of the array to resolve single quantal secretory events. Subcellular localization of exocytosis was provided by assigning each quantal event to one of the nine channels based on its location. The resulting mapping highlights the heterogeneous distribution of secretory activity in cell microdomains of 12-27 μm2. In bovine chromaffin cells, secretion was highly heterogeneous with zones of high and medium activity in 54% of the cell surface and zones of low or no activity in the remainder. The 'non-active' ('silent') zones covered 24% of the total and persisted for 6-8 min, indicating stable location. The 9-Ch NCD-UMEA therefore appears suitable for investigating the microdomain organization of neurosecretion with high spatial resolution.
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Affiliation(s)
- Sara Gosso
- Department of Drug Science and Technology, NIS Center, University of Turin, 10125, Turin, Italy
| | - Marco Turturici
- Department of Drug Science and Technology, NIS Center, University of Turin, 10125, Turin, Italy Department of Neuroscience, University of Turin, 10125, Turin, Italy
| | - Claudio Franchino
- Department of Drug Science and Technology, NIS Center, University of Turin, 10125, Turin, Italy
| | - Elisabetta Colombo
- Department of Drug Science and Technology, NIS Center, University of Turin, 10125, Turin, Italy Institute of Electron Devices and Circuits, University of Ulm, 89069, Ulm, Germany
| | - Alberto Pasquarelli
- Institute of Electron Devices and Circuits, University of Ulm, 89069, Ulm, Germany
| | - Emilio Carbone
- Department of Drug Science and Technology, NIS Center, University of Turin, 10125, Turin, Italy
| | - Valentina Carabelli
- Department of Drug Science and Technology, NIS Center, University of Turin, 10125, Turin, Italy
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8
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Amperometric resolution of a prespike stammer and evoked phases of fast release from retinal bipolar cells. J Neurosci 2013; 33:8144-58. [PMID: 23658155 DOI: 10.1523/jneurosci.5062-12.2013] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The neurotransmitter glutamate is used by most neurons in the brain to activate a multitude of different types of glutamate receptors and transporters involved in fast and relatively slower signaling. Synaptic ribbons are large presynaptic structures found in neurons involved in vision, balance, and hearing, which use a large number of glutamate-filled synaptic vesicles to meet their signaling demands. To directly measure synaptic vesicle release events, the ribbon-type presynaptic terminals of goldfish retinal bipolar cells were coaxed to release a false transmitter that could be monitored with amperometry by placing the carbon fiber directly on the larger synaptic terminal. Spontaneous secretion events formed a unimodal charge distribution, but single spike properties were heterogeneous. Larger events rose exponentially without interruption (τ ∼ 30 μs), and smaller events exhibited a stammer in their rising phase that is interpreted as a brief pause in pore dilation, a characteristic commonly associated with large dense core granule fusion pores. These events were entirely Ca(2+)-dependent. Holding the cells at -60 mV halted spontaneous release; and when the voltage was stepped to >-40 mV, secretion ensued. When stepping the voltage to 0 mV, novel kinetic phases of vesicle recruitment were revealed. Approximately 14 vesicles were released per ribbon in two kinetic phases with time constants of 1.5 and 16 ms, which are proposed to represent different primed states within the population of docked vesicles.
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9
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Kasai H, Takahashi N, Tokumaru H. Distinct Initial SNARE Configurations Underlying the Diversity of Exocytosis. Physiol Rev 2012; 92:1915-64. [DOI: 10.1152/physrev.00007.2012] [Citation(s) in RCA: 120] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
The dynamics of exocytosis are diverse and have been optimized for the functions of synapses and a wide variety of cell types. For example, the kinetics of exocytosis varies by more than five orders of magnitude between ultrafast exocytosis in synaptic vesicles and slow exocytosis in large dense-core vesicles. However, in all cases, exocytosis is mediated by the same fundamental mechanism, i.e., the assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. It is often assumed that vesicles need to be docked at the plasma membrane and SNARE proteins must be preassembled before exocytosis is triggered. However, this model cannot account for the dynamics of exocytosis recently reported in synapses and other cells. For example, vesicles undergo exocytosis without prestimulus docking during tonic exocytosis of synaptic vesicles in the active zone. In addition, epithelial and hematopoietic cells utilize cAMP and kinases to trigger slow exocytosis of nondocked vesicles. In this review, we summarize the manner in which the diversity of exocytosis reflects the initial configurations of SNARE assembly, including trans-SNARE, binary-SNARE, unitary-SNARE, and cis-SNARE configurations. The initial SNARE configurations depend on the particular SNARE subtype (syntaxin, SNAP25, or VAMP), priming proteins (Munc18, Munc13, CAPS, complexin, or snapin), triggering proteins (synaptotagmins, Doc2, and various protein kinases), and the submembraneous cytomatrix, and they are the key to determining the kinetics of subsequent exocytosis. These distinct initial configurations will help us clarify the common SNARE assembly processes underlying exocytosis and membrane trafficking in eukaryotic cells.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Noriko Takahashi
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
| | - Hiroshi Tokumaru
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Graduate School of Medicine, The University of Tokyo, Tokyo, Japan; and Faculty of Pharmaceutical Sciences at Kagawa, Tokushima Bunri University, Kagawa, Japan
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10
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11
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Cans AS, Ewing AG. Highlights of 20 years of electrochemical measurements of exocytosis at cells and artificial cells. J Solid State Electrochem 2011. [DOI: 10.1007/s10008-011-1369-9] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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12
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van Kempen GTH, vanderLeest H, van den Berg R, Eilers P, Westerink R. Three distinct modes of exocytosis revealed by amperometry in neuroendocrine cells. Biophys J 2011; 100:968-77. [PMID: 21320441 PMCID: PMC3037570 DOI: 10.1016/j.bpj.2011.01.010] [Citation(s) in RCA: 40] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2010] [Revised: 12/30/2010] [Accepted: 01/04/2011] [Indexed: 11/19/2022] Open
Abstract
Neurotransmission requires Ca(2+)-dependent release of secretory products through fusion pores that open and reclose (partial membrane distention) or open irreversibly (complete membrane distention). It has been challenging to distinguish between these release modes; however, in the work presented here, we were able to deduce different modes of depolarization-evoked exocytosis in neuroendocrine chromaffin and PC12 cells solely by analyzing amperometric recordings. After we determined the quantal size (Q), event half-width (t(50)), event amplitude (I(peak)), and event decay time constant (τ(decay)), we fitted scatter plots of log-transformed data with a mixture of one- and two-dimensional Gaussian distributions. Our analysis revealed three distinct and differently shaped clusters of secretory events, likely corresponding to different modes of exocytosis. Complete membrane distention, through fusion pores of widely varying conductances, accounted for 70% of the total amount of released catecholamine. Two different kinds of partial membrane distention (kiss-and-run and kiss-and-stay exocytosis), characterized by mode-specific fusion pores with unitary conductances, accounted for 20% and 10%, respectively. These results show that our novel one- and two-dimensional analysis of amperometric data reveals new release properties and enables one to distinguish at least three different modes of exocytosis solely by analyzing amperometric recordings.
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Affiliation(s)
- G. Th. H. van Kempen
- Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - H.T. vanderLeest
- Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - R.J. van den Berg
- Department of Molecular Cell Biology, Leiden University Medical Center, Leiden, The Netherlands
| | - P. Eilers
- Department of Biostatistics, Erasmus University, Rotterdam, The Netherlands
| | - R.H.S. Westerink
- Neurotoxicology Research Group, Toxicology Division, Institute for Risk Assessment Sciences, Utrecht University, Utrecht, The Netherlands
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13
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Affiliation(s)
- Sascha Martens
- Max F. Perutz Laboratories, University of Vienna, Vienna, Austria
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14
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Galvanovskis J, Braun M, Rorsman P. Exocytosis from pancreatic β-cells: mathematical modelling of the exit of low-molecular-weight granule content. Interface Focus 2010; 1:143-52. [PMID: 22419980 DOI: 10.1098/rsfs.2010.0006] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2010] [Accepted: 11/11/2010] [Indexed: 11/12/2022] Open
Abstract
Pancreatic β-cells use Ca(2+)-dependent exocytosis of large dense core vesicles to release insulin. Exocytosis in β-cells has been studied biochemically, biophysically and optically. We have previously developed a biophysical method to monitor release of endogenous intragranular constituents that are co-released with insulin. This technique involves the expression of ionotropic membrane receptors in the β-cell plasma membrane and enables measurements of exocytosis of individual vesicles with sub-millisecond resolution. Like carbon fibre amperometry, this method allows fine details of the release process, like the expansion of the fusion pore (the narrow connection between the granule lumen and the extracellular space), to be monitored. Here, we discuss experimental data obtained with this method within the framework of a simple mathematical model that describes the release of low-molecular constituents during exocytosis of the insulin granules. Our findings suggest that the fusion pore functions as a molecular sieve, allowing differential release of low- and high-molecular-weight granule constituents.
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Affiliation(s)
- Juris Galvanovskis
- Department of Physiology, Anatomy and Genetics, University of Oxford, Henry Wellcome Building, Parks Road, Oxford OX1 3PT , UK
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15
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Zhang Z, Jackson MB. Membrane bending energy and fusion pore kinetics in Ca(2+)-triggered exocytosis. Biophys J 2010; 98:2524-34. [PMID: 20513396 DOI: 10.1016/j.bpj.2010.02.043] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2009] [Revised: 02/15/2010] [Accepted: 02/26/2010] [Indexed: 11/30/2022] Open
Abstract
A fusion pore composed of lipid is an obligatory kinetic intermediate of membrane fusion, and its formation requires energy to bend membranes into highly curved shapes. The energetics of such deformations in viral fusion is well established, but the role of membrane bending in Ca(2+)-triggered exocytosis remains largely untested. Amperometry recording showed that during exocytosis in chromaffin and PC12 cells, fusion pores formed by smaller vesicles dilated more rapidly than fusion pores formed by larger vesicles. The logarithm of 1/(fusion pore lifetime) varied linearly with vesicle curvature. The vesicle size dependence of fusion pore lifetime quantitatively accounted for the nonexponential fusion pore lifetime distribution. Experimentally manipulating vesicle size failed to alter the size dependence of fusion pore lifetime. Manipulations of membrane spontaneous curvature altered this dependence, and applying the curvature perturbants to the opposite side of the membrane reversed their effects. These effects of curvature perturbants were opposite to those seen in viral fusion. These results indicate that during Ca(2+)-triggered exocytosis membrane bending opposes fusion pore dilation rather than fusion pore formation. Ca(2+)-triggered exocytosis begins with a proteinaceous fusion pore with less stressed membrane, and becomes lipidic as it dilates, bending membrane into a highly curved shape.
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Affiliation(s)
- Zhen Zhang
- Department of Physiology, University of Wisconsin, School of Medicine and Public Health, Madison, Wisconsin, USA
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16
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Lefkowitz JJ, Fogarty KE, Lifshitz LM, Bellve KD, Tuft RA, ZhuGe R, Walsh JV, De Crescenzo V. Suppression of Ca2+ syntillas increases spontaneous exocytosis in mouse adrenal chromaffin cells. ACTA ACUST UNITED AC 2010; 134:267-80. [PMID: 19786582 PMCID: PMC2757764 DOI: 10.1085/jgp.200910285] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
A central concept in the physiology of neurosecretion is that a rise in cytosolic [Ca2+] in the vicinity of plasmalemmal Ca2+ channels due to Ca2+ influx elicits exocytosis. Here, we examine the effect on spontaneous exocytosis of a rise in focal cytosolic [Ca2+] in the vicinity of ryanodine receptors (RYRs) due to release from internal stores in the form of Ca2+ syntillas. Ca2+ syntillas are focal cytosolic transients mediated by RYRs, which we first found in hypothalamic magnocellular neuronal terminals. (scintilla, Latin for spark; found in nerve terminals, normally synaptic structures.) We have also observed Ca2+ syntillas in mouse adrenal chromaffin cells. Here, we examine the effect of Ca2+ syntillas on exocytosis in chromaffin cells. In such a study on elicited exocytosis, there are two sources of Ca2+: one due to influx from the cell exterior through voltage-gated Ca2+ channels, and that due to release from intracellular stores. To eliminate complications arising from Ca2+ influx, we have examined spontaneous exocytosis where influx is not activated. We report here that decreasing syntillas leads to an increase in spontaneous exocytosis measured amperometrically. Two independent lines of experimentation each lead to this conclusion. In one case, release from stores was blocked by ryanodine; in another, stores were partially emptied using thapsigargin plus caffeine, after which syntillas were decreased. We conclude that Ca2+ syntillas act to inhibit spontaneous exocytosis, and we propose a simple model to account quantitatively for this action of syntillas.
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Affiliation(s)
- Jason J Lefkowitz
- Department of Physiology, University of Massachusetts Medical School, Worcester, 01655, USA
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Kasai H, Hatakeyama H, Ohno M, Takahashi N. Exocytosis in islet beta-cells. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 654:305-38. [PMID: 20217504 DOI: 10.1007/978-90-481-3271-3_14] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The development of technologies that allow for live optical imaging of exocytosis from beta-cells has greatly improved our understanding of insulin secretion. Two-photon imaging, in particular, has enabled researchers to visualize the exocytosis of large dense-core vesicles (LDCVs) containing insulin from beta-cells in intact islets of Langerhans. These studies have revealed that high glucose levels induce two phases of insulin secretion and that this release is dependent upon cytosolic Ca(2+) and cAMP. This technology has also made it possible to examine the spatial profile of insulin exocytosis in these tissues and compare that profile with those of other secretory glands. Such studies have led to the discovery of the massive exocytosis of synaptic-like microvesicles (SLMVs) in beta-cells. These imaging studies have also helped clarify facets of insulin exocytosis that cannot be properly addressed using the currently available electrophysiological techniques. This chapter provides a concise introduction to the field of optical imaging for those researchers who wish to characterize exocytosis from beta-cells in the islets of Langerhans.
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Affiliation(s)
- Haruo Kasai
- Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, The University of Tokyo, Hongo, Tokyo 113-0033, Japan.
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Monitoring of vesicular exocytosis from single cells using micrometer and nanometer-sized electrochemical sensors. Anal Bioanal Chem 2009; 394:17-32. [PMID: 19274456 DOI: 10.1007/s00216-009-2703-2] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Revised: 02/07/2009] [Accepted: 02/10/2009] [Indexed: 02/05/2023]
Abstract
Communication between cells by release of specific chemical messengers via exocytosis plays crucial roles in biological process. Electrochemical detection based on ultramicroelectrodes (UMEs) has become one of the most powerful techniques in real-time monitoring of an extremely small number of released molecules during very short time scales, owing to its intrinsic advantages such as fast response, excellent sensitivity, and high spatiotemporal resolution. Great successes have been achieved in the use of UME methods to obtain quantitative and kinetic information about released chemical messengers and to reveal the molecular mechanism in vesicular exocytosis. In this paper, we review recent developments in monitoring exocytosis by use of UMEs-electrochemical-based techniques including electrochemical detection using micrometer and nanometer-sized sensors, scanning electrochemical microscopy (SECM), and UMEs implemented in lab-on-a-chip (LOC) microsystems. These advances are of great significance in obtaining a better understanding of vesicular exocytosis and chemical communications between cells, and will facilitate developments in many fields, including analytical chemistry, biological science, and medicine. Furthermore, future developments in electrochemical probing of exocytosis are also proposed.
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Quantal ATP release in rat beta-cells by exocytosis of insulin-containing LDCVs. Pflugers Arch 2008; 458:389-401. [PMID: 19018564 DOI: 10.1007/s00424-008-0610-6] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/08/2008] [Accepted: 10/25/2008] [Indexed: 10/21/2022]
Abstract
Quantal release of adenosine triphosphate (ATP) was monitored in rat pancreatic beta-cells expressing P2X(2) receptors. Stimulation of exocytosis evoked rapidly activating and deactivating ATP-dependent transient inward currents (TICs). The unitary charge (q) of the events recorded at 0.2 microM [Ca(2+)](i) averaged 4.3 pC. The distribution of the 3 square root q of these events could be described by a single Gaussian. The rise times averaged approximately 5 ms over a wide range of TIC amplitudes. In beta-cells preloaded with 5-hydroxytryptamine (5-HT; accumulating in insulin granules), ATP was coreleased with 5-HT during >90% of the release events. Following step elevation of [Ca(2+)](i) to approximately 5 microM by photo release of caged Ca(2+), an increase in membrane capacitance was observed after 33 ms, whereas ATP release first became detectable after 43 ms. The step increase in [Ca(2+)](i) produced an initial large TIC followed by a series of smaller events that echoed the changes in membrane capacitance (DeltaC(m)). Mathematical modeling suggests that the large initial TIC reflects the superimposition of many unitary events. Exocytosis, measured as DeltaC(m) or TICs, was complete within 2 s after elevation of [Ca(2+)](i) with no sign of endocytosis masking the capacitance increase. The relationship between total charge (Q) and DeltaC(m) was linear with a slope of approximately 1.2 pC/fF. The latter value predicts a capacitance increase of 3.6 fF for the observed mean value of q, close to that expected for exocytosis of individual insulin granules. Our results indicate that measurements of ATP release and DeltaC(m) principally (> or =85-95%) report exocytosis of insulin granules.
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Li ZY, Zhou W, Wu ZX, Zhang RY, Xu T. Fabrication of size-controllable ultrasmall-disk electrode: monitoring single vesicle release kinetics at tiny structures with high spatio-temporal resolution. Biosens Bioelectron 2008; 24:1358-64. [PMID: 18804366 DOI: 10.1016/j.bios.2008.07.073] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2008] [Revised: 07/27/2008] [Accepted: 07/29/2008] [Indexed: 11/25/2022]
Abstract
Size-controllable micron or nano-disk carbon fiber electrode (CFE) is prepared and demonstrated to be excellent for extra-cellular transmitter release detection at tiny structures and vesicle fusion kinetics analysis with high spatio-temporal resolution. An improved electrochemical etching procedure was employed, for the first time, to fabricate cylindrical fiber with controlled micron or nano-diameter. Afterwards, a facile insulation with polypropylene sheath was employed to completely insulate the whole body of the thinned fiber, and an ultrasmall-disk sensing area was finally produced by cutting of the insulated fibers. Scanning electron microscopy (SEM) was employed to characterize the ultrasmall geometry size of the fabricated electrode and to show the tight adherence of the insulation sheath on the fiber. The cut ends of the electrodes were also shown to be smooth, clean and without obvious jagged layer. The fabricated micron or nano-disk carbon electrodes show ideal steady-state voltammetric behavior with satisfying reversibility. Subsequently, the performance of the ultrasmall-disk CFE for amperometric detection of cell secretion was characterized. Results showed that, compared to the conventional micro-disk CFE, the etched small disk CFE possesses higher sensitivity due to its obviously improved signal-to-noise level, which enables minute amounts of 3000 oxidizable molecules to be detectable. The nano-disk CFE was shown to be particularly ideal for analysis of fusion kinetics, due to its avoidance of diffusion broadening of the detected spikes, which is the inherent defect of the conventional micro-CFE technique.
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Affiliation(s)
- Zhao-Yu Li
- Key Laboratory of Molecular Biophysics of the Ministry of Education, College of Life Science and Technology, Huazhong University of Science and Technology, Wuhan 430074, PR China
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22
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Amatore C, Arbault S, Guille M, Lemaître F. Electrochemical Monitoring of Single Cell Secretion: Vesicular Exocytosis and Oxidative Stress. Chem Rev 2008; 108:2585-621. [DOI: 10.1021/cr068062g] [Citation(s) in RCA: 316] [Impact Index Per Article: 19.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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23
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Affiliation(s)
- Graham C. R. Ellis-Davies
- Department of Pharmacology and Physiology, Drexel University College of Medicine, 245 North 15th Street, Philadelphia, Pennsylvania 19102
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Liao H, Zhang J, Shestopal S, Szabo G, Castle A, Castle D. Nonredundant function of secretory carrier membrane protein isoforms in dense core vesicle exocytosis. Am J Physiol Cell Physiol 2008; 294:C797-809. [DOI: 10.1152/ajpcell.00493.2007] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Five secretory carrier membrane proteins (SCAMP-1, -2, -3, -4, and -5) have been characterized in mammalian cells. Previously, SCAMP-1 and -2 have been implicated to function in exocytosis. RNA inhibitor-mediated deficiency of one or both of these SCAMPs interferes with dense core vesicle (DCV) exocytosis in neuroendocrine PC12 cells as detected by amperometry. Knockdowns of these SCAMPs each decreased the number and frequency of depolarization-induced exocytotic events. SCAMP-2 but not SCAMP-1 depletion also delayed the onset of exocytosis. Both knockdowns, however, altered fusion pore dynamics, increasing rapid pore closure and decreasing pore dilation. In contrast, knockdowns of SCAMP-3 and -5 only interfered with the frequency of fusion pore opening and did not affect the dynamics of newly opened pores. None of the knockdowns noticeably affected upstream events, including the distribution of DCVs near the plasma membrane and calcium signaling kinetics, although norepinephrine uptake/storage was moderately decreased by deficiency of SCAMP-1 and -5. Thus, SCAMP-1 and -2 are most closely linked to the final events of exocytosis. Other SCAMPs collaborate in regulating fusion sites, but the roles of individual isoforms appear at least partially distinct.
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Neco P, Fernández-Peruchena C, Navas S, Gutiérrez LM, de Toledo GA, Alés E. Myosin II contributes to fusion pore expansion during exocytosis. J Biol Chem 2008; 283:10949-57. [PMID: 18283106 DOI: 10.1074/jbc.m709058200] [Citation(s) in RCA: 80] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
During exocytosis, the fusion pore expands to allow release of neurotransmitters and hormones to the extracellular space. To understand the process of synaptic transmission, it is of outstanding importance to know the properties of the fusion pore and how these properties affect the release process. Many proteins have been implicated in vesicle fusion; however, there is little evidence for proteins involved in fusion pore expansion. Myosin II has been shown to participate in the transport of vesicles and, surprisingly, in the final phases of exocytosis, affecting the kinetics of catecholamine release in adrenal chromaffin cells as measured by amperometry. Here, we have studied single vesicle exocytosis in chromaffin cells overexpressing an unphosphorylatable form (T18AS19A RLC-GFP) of myosin II that produces an inactive protein by patch amperometry. This method allows direct determination of fusion pore expansion by measuring its conductance, whereas the release of catecholamines is recorded simultaneously by amperometry. Here we demonstrated that the fusion pore is of critical importance to control the release of catecholamines during single vesicle secretion in chromaffin cells. We proved that myosin II acts as a molecular motor on the fusion pore expansion by hindering its dilation when it lacks the phosphorylation sites.
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Affiliation(s)
- Patricia Neco
- Departamento Fisiología Médica y Biofísica, Universidad de Sevilla, Sevilla 41009, Spain
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26
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Zhang Z, Jackson MB. Temperature dependence of fusion kinetics and fusion pores in Ca2+-triggered exocytosis from PC12 cells. ACTA ACUST UNITED AC 2008; 131:117-24. [PMID: 18195388 PMCID: PMC2213568 DOI: 10.1085/jgp.200709891] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The temperature dependence of Ca2+-triggered exocytosis was studied using carbon fiber amperometry to record the release of norepinephrine from PC12 cells. Single-vesicle fusion events were examined at temperatures varying from 12 to 28°C, and with release elicited by depolarization. Measurements were made of the initial and maximum frequencies of exocytotic events, of fusion pore lifetime, flux through the open fusion pore, kiss-and-run versus full-fusion probability, and parameters associated with the shapes of amperometric spikes. The fusion pore open-state flux, and all parameters associated with spike shape, including area, rise time, and decay time, had weak temperature dependences and activation energies in the range expected for bulk diffusion in an aqueous solution. Kiss-and-run events also varied with temperature, with lower temperatures increasing the relative probability of kiss-and-run events by ∼50%. By contrast, kinetic parameters relating to the frequency of exocytotic events and fusion pore transitions depended much more strongly on temperature, suggesting that these processes entail structural rearrangements of proteins or lipids or both. The weak temperature dependence of spike shape suggests that after the fusion pore has started to expand, structural transitions of membrane components are no longer kinetically limiting. This indicates that the content of a vesicle is expelled completely after fusion pore expansion.
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Affiliation(s)
- Zhen Zhang
- Department of Physiology, University of Wisconsin School of Medicine and Publis Health, Madison 53706, USA
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27
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Chen X, Gao Y, Hossain M, Gangopadhyay S, Gillis KD. Controlled on-chip stimulation of quantal catecholamine release from chromaffin cells using photolysis of caged Ca2+ on transparent indium-tin-oxide microchip electrodes. LAB ON A CHIP 2008; 8:161-9. [PMID: 18094774 PMCID: PMC2489207 DOI: 10.1039/b715308m] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/16/2023]
Abstract
Photorelease of caged Ca(2+) is a uniquely powerful tool to study the dynamics of Ca(2+)-triggered exocytosis from individual cells. Using photolithography and other microfabrication techniques, we have developed transparent microchip devices to enable photorelease of caged Ca(2+), together with electrochemical detection of quantal catecholamine secretion from individual cells or cell arrays as a step towards developing high-throughput experimental devices. A 100 nm thick transparent indium-tin-oxide (ITO) film was sputter-deposited onto glass coverslips, which were then patterned into 24 cell-sized working electrodes (approximately 20 microm by 20 microm). We loaded bovine chromaffin cells with acetoxymethyl (AM) ester derivatives of the Ca(2+) cage NP-EGTA and Ca(2+) indicator dye fura-4F, then transferred these cells onto the working ITO electrodes for amperometric recordings. Upon flash photorelease of caged Ca(2+), a uniform rise of [Ca(2+)](i) within the target cell leads to quantal release of oxidizable catecholamines measured amperometrically by the underlying ITO electrode. We observed a burst of amperometric spikes upon rapid elevation of [Ca(2+)](i) and a "priming" effect of sub-stimulatory [Ca(2+)](i) on the response of cells to subsequent [Ca(2+)](i) elevation, similar to previous reports using different techniques. We conclude that UV photolysis of caged Ca(2+) is a suitable stimulation technique for higher-throughput studies of Ca(2+)-dependent exocytosis on transparent electrochemical microelectrode arrays.
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Affiliation(s)
- Xiaohui Chen
- Department of Biological Engineering, University of Missouri, Columbia, MO 65211, USA
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28
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29
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30
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Hatakeyama H, Takahashi N, Kishimoto T, Nemoto T, Kasai H. Two cAMP-dependent pathways differentially regulate exocytosis of large dense-core and small vesicles in mouse beta-cells. J Physiol 2007; 582:1087-98. [PMID: 17510178 PMCID: PMC2075257 DOI: 10.1113/jphysiol.2007.135228] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
It has been reported that cAMP regulates Ca(2+)-dependent exocytosis via protein kinase A (PKA) and exchange proteins directly activated by cAMP (Epac) in neurons and secretory cells. It has, however, never been clarified how regulation of Ca(2+)-dependent exocytosis by cAMP differs depending on the involvement of PKA and Epac, and depending on two types of secretory vesicles, large dense-core vesicles (LVs) and small vesicles (SVs). In this study, we have directly visualized Ca(2+)-dependent exocytosis of both LVs and SVs with two-photon imaging in mouse pancreatic beta-cells. We found that marked exocytosis of SVs occurred with a time constant of 0.3 s, more than three times as fast as LV exocytosis, on stimulation by photolysis of a caged-Ca(2+) compound. The diameter of SVs was identified as approximately 80 nm with two-photon imaging, which was confirmed by electron-microscopic investigation with photoconversion of diaminobenzidine. Calcium-dependent exocytosis of SVs was potentiated by the cAMP-elevating agent forskolin, and the potentiating effect was unaffected by antagonists of PKA and was mimicked by the Epac-selective agonist 8-(4-chlorophenylthio)-2'-O-methyl cAMP, unlike that on LVs. Moreover, high-glucose stimulation induced massive exocytosis of SVs in addition to LVs, and photolysis of caged cAMP during glucose stimulation caused potentiation of exocytosis with little delay for SVs but with a latency of 5 s for LVs. Thus, Epac and PKA selectively regulate exocytosis of SVs and LVs, respectively, in beta-cells, and Epac can regulate exocytosis more rapidly than PKA.
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Affiliation(s)
- Hiroyasu Hatakeyama
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Bunkyo-ku, Tokyo, 113-0033 Japan
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31
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Awatramani GB, Boyd JD, Delaney KR, Murphy TH. Effective release rates at single rat Schaffer collateral-CA1 synapses during sustained theta-burst activity revealed by optical imaging. J Physiol 2007; 582:583-95. [PMID: 17463045 PMCID: PMC2075339 DOI: 10.1113/jphysiol.2007.130286] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
To understand how information is coded at single hippocampal synapses during high-frequency activity, we imaged NMDA receptor-mediated Ca(2+) responses in spines of CA1 neurons using two-photon microscopy. Although discrete quantal events were not readily apparent during continuous theta-burst stimulation (TBS), we found that the steady-state dendritic Ca(2+) response was spatially restricted (half-width < 1 microm), voltage dependent and sensitive to MK-801, indicating that that it was mediated by activation of NMDA receptors at single synapses. Partial antagonism of NMDA receptors caused a similar reduction of NMDA EPSCs (measured at the soma) and local dendritic Ca(2+) signals, suggesting that, like EPSCs, the steady-state Ca(2+) signal was made up of a linear addition of quantal events. Statistical analyses of the steady-response suggested that the quantal size did not change dramatically during TBS. Deconvolution of TBS-evoked Ca(2+) responses revealed a heterogeneous population of synapses differing in their capacity to signal high-frequency information, with an average effective steady-state release rate of approximately 2.6 vesicles synapse(-1)s(-1). To assess how the optically determined release rates compare with population measures we analysed the rate of decay of peak EPSCs during train stimulation. From these studies, we estimated a unitary vesicular replenishment rate of 0.02 s(-1), which corresponds to an average release rate of approximately 0.8-2 vesicles s(-1) at individual synapses. Additionally, extracellular recordings from single Schaffer collaterals revealed that spikes propagate reliably during TBS. Hence, during high-frequency activity, Schaffer collaterals conduct spikes with high fidelity, but release quanta with relatively lower efficiency, leaving NMDA receptor function largely intact and synapse specific. Heterogeneity in release rates between synapses suggests that similar patterns of presynaptic action potentials could trigger different forms of plasticity at individual synapses.
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Affiliation(s)
- G B Awatramani
- University of British Columbia, 2255 Wesbrook Mall, Vancouver, British Columbia, Canada
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Amatore C, Arbault S, Lemaître F, Verchier Y. Comparison of apex and bottom secretion efficiency at chromaffin cells as measured by amperometry. Biophys Chem 2007; 127:165-71. [PMID: 17316959 DOI: 10.1016/j.bpc.2007.01.007] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/01/2006] [Revised: 01/26/2007] [Accepted: 01/26/2007] [Indexed: 11/16/2022]
Abstract
In chromaffin cells, the exocytosis of neuromediators involves the fusion between a secretory vesicle and the cell membrane. Many techniques based on electrophysiology, electrochemistry and fluorescence microscopy allow the study of such a complex process at active zones of single immobilized cells. These techniques can provide an effective analysis either at the apex, either at the base of the cell adhering onto a substrate. For instance, patch-clamp (electrophysiology) and amperometry (electrochemistry) deal with detection at the exposed top of the cell, whereas evanescent field microscopy concerns mainly its bottom, i.e., the zone on which the cell rests onto the surface. However, in chromaffin cells, comparison between the two sets of methods remains to be established and whether apex fusion events are comparable or not to those observed at the base of the cell is an open question. In this work, we compare both active zones upon using the same measurement method, viz., by performing electrochemical detection at these both poles (top and bottom) of bovine chromaffin cells. This is performed upon using carbon fiber microelectrodes (apical analysis) and planar ITO transparent (basal analysis) electrodes, respectively. Our results indicate that the processes monitored at each pole differ though the same technique is used.
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Affiliation(s)
- Christian Amatore
- Ecole Normale Supérieure, Département de Chimie, UMR CNRS-ENS-UPMC 8640 PASTEUR, 24 rue Lhomond, 75231 Paris cedex 05. France.
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Lichtenberger J, Fromherz P. A cell-semiconductor synapse: transistor recording of vesicle release in chromaffin cells. Biophys J 2006; 92:2262-8. [PMID: 17189317 PMCID: PMC1861798 DOI: 10.1529/biophysj.106.096446] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The release of dense-core vesicles in bovine chromaffin cells is a model for the presynaptic process in neurons. It is usually studied by microamperometry of catecholamines with carbon fibers. Here we introduce transistor recording as a tool to study vesicle release. When we stimulate a chromaffin cell placed on a field-effect transistor, the gate voltage exhibits peaks that correlate with a simultaneously performed amperometric recording. We attribute the transistor signal to a release of protons from the extruded matrix of vesicles that lowers the extracellular pH and changes the electrical surface potential of the gate oxide. The rise time of the transistor signals is similar to that of amperometric responses, whereas their duration is distinctly longer. In a model computation, the rise time is identified with the extrusion of vesicle matrix into the narrow extracellular space between cell and gate oxide, and the decay time is attributed to pH equilibration through slow diffusion in the extruded matrix. Because the transistor recording relies on protons, it can be applied to acidic vesicles with electrochemically inactive hormones or transmitters.
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Affiliation(s)
- Janosch Lichtenberger
- Department of Membrane and Neurophysics, Max Planck Institute for Biochemistry, Martinsried/Munich, D 82152 Germany
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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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De Crescenzo V, Fogarty KE, ZhuGe R, Tuft RA, Lifshitz LM, Carmichael J, Bellvé KD, Baker SP, Zissimopoulos S, Lai FA, Lemos JR, Walsh JV. Dihydropyridine receptors and type 1 ryanodine receptors constitute the molecular machinery for voltage-induced Ca2+ release in nerve terminals. J Neurosci 2006; 26:7565-74. [PMID: 16855084 PMCID: PMC6674279 DOI: 10.1523/jneurosci.1512-06.2006] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Ca2+ stores were studied in a preparation of freshly dissociated terminals from hypothalamic magnocellular neurons. Depolarization from a holding level of -80 mV in the absence of extracellular Ca2+ elicited Ca2+ release from intraterminal stores, a ryanodine-sensitive process designated as voltage-induced Ca2+ release (VICaR). The release took one of two forms: an increase in the frequency but not the quantal size of Ca2+ syntillas, which are brief, focal Ca2+ transients, or an increase in global [Ca2+]. The present study provides evidence that the sensors of membrane potential for VICaR are dihydropyridine receptors (DHPRs). First, over the range of -80 to -60 mV, in which there was no detectable voltage-gated inward Ca2+ current, syntilla frequency was increased e-fold per 8.4 mV of depolarization, a value consistent with the voltage sensitivity of DHPR-mediated VICaR in skeletal muscle. Second, VICaR was blocked by the dihydropyridine antagonist nifedipine, which immobilizes the gating charge of DHPRs but not by Cd2+ or FPL 64176 (methyl 2,5 dimethyl-4[2-(phenylmethyl)benzoyl]-1H-pyrrole-3-carboxylate), a non-dihydropyridine agonist specific for L-type Ca2+ channels, having no effect on gating charge movement. At 0 mV, the IC50 for nifedipine blockade of VICaR in the form of syntillas was 214 nM in the absence of extracellular Ca2+. Third, type 1 ryanodine receptors, the type to which DHPRs are coupled in skeletal muscle, were detected immunohistochemically at the plasma membrane of the terminals. VICaR may constitute a new link between neuronal activity, as signaled by depolarization, and a rise in intraterminal Ca2+.
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Ardiles AO, Maripillán J, Lagos VL, Toro R, Mora IG, Villarroel L, Alés E, Borges R, Cárdenas AM. A rapid exocytosis mode in chromaffin cells with a neuronal phenotype. J Neurochem 2006; 99:29-41. [PMID: 16889641 DOI: 10.1111/j.1471-4159.2006.04080.x] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
We have used astrocyte-conditioned medium (ACM) to promote the transdifferentiation of bovine chromaffin cells and study modifications in the exocytotic process when these cells acquire a neuronal phenotype. In the ACM-promoted neuronal phenotype, secretory vesicles and intracellular Ca2+ rise were preferentially distributed in the neurite terminals. Using amperometry, we observed that the exocytotic events also occurred mainly in the neurite terminals, wherein the individual exocytotic events had smaller quantal size than in undifferentiated cells. Additionally, duration of pre-spike current was significantly shorter, suggesting that ACM also modifies the fusion pore stability. After long exposure (7-9 days) to ACM, the kinetics of catecholamine release from individual vesicles was markedly accelerated. The morphometric analysis of vesicle diameters suggests that the rapid exocytotic events observed in neurites of ACM-treated cells correspond to the exocytosis of large dense-core vesicles (LDCV). On the other hand, experiments performed in EGTA-loaded cells suggest that ACM treatment promotes a better coupling between voltage-gated calcium channels (VGCC) and LDCV. Thus, our findings reveal that ACM promotes a neuronal phenotype in chromaffin cells, wherein the exocytotic kinetics is accelerated. Such rapid exocytosis mode could be caused at least in part by a better coupling between secretory vesicles and VGCC.
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Affiliation(s)
- Alvaro O Ardiles
- Centro de Neurociencia de Valparaíso, Universidad de Valparaíso, Chile
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37
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Nagy G, Kim JH, Pang ZP, Matti U, Rettig J, Südhof TC, Sørensen JB. Different effects on fast exocytosis induced by synaptotagmin 1 and 2 isoforms and abundance but not by phosphorylation. J Neurosci 2006; 26:632-43. [PMID: 16407561 PMCID: PMC6674391 DOI: 10.1523/jneurosci.2589-05.2006] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Synaptotagmins comprise a large protein family, of which synaptotagmin 1 (Syt1) is a Ca2+ sensor for fast exocytosis, and its close relative, synaptotagmin 2 (Syt2), is assumed to serve similar functions. Chromaffin cells express Syt1 but not Syt2. We compared secretion from chromaffin cells from Syt1 null mice overexpressing either Syt isoform. High time-resolution capacitance measurement showed that Syt1 null cells lack the exocytotic phase corresponding to the readily-releasable pool (RRP) of vesicles. Comparison with the amperometric signal confirmed that the missing phase of exocytosis consists of catecholamine-containing vesicles. Overexpression of Syt1 rescued the RRP and increased its size above wild-type values, whereas the size of the slowly releasable pool decreased, indicating that the availability of Syt1 regulates the relative size of the two releasable pools. The RRP was also rescued by Syt2 overexpression, but the kinetics of fusion was slightly slower than in cells expressing Syt1. Biochemical experiments showed that Syt2 has a slightly lower Ca2+ affinity for phospholipid binding than Syt1 because of a difference in the C2A domain. These data constitute evidence for the function of Syt1 and Syt2 as alternative, but not identical, calcium-sensors for RRP fusion. By overexpression of Syt1 mutated in the shared PKC/calcium/calmodulin-dependent kinase phosphorylation site, we show that phorbol esters act independently and upstream of Syt1 to regulate the size of the releasable pools. We conclude that exocytosis from mouse chromaffin cells can be modified by the differential expression of Syt isoforms and by Syt abundance but not by phosphorylation of Syt1.
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Affiliation(s)
- Gábor Nagy
- Max-Planck-Institute for Biophysical Chemistry, D-37077 Göttingen, Germany
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38
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ZhuGe R, DeCrescenzo V, Sorrentino V, Lai FA, Tuft RA, Lifshitz LM, Lemos JR, Smith C, Fogarty KE, Walsh JV. Syntillas release Ca2+ at a site different from the microdomain where exocytosis occurs in mouse chromaffin cells. Biophys J 2006; 90:2027-37. [PMID: 16387759 PMCID: PMC1386781 DOI: 10.1529/biophysj.105.071654] [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] [Received: 07/29/2005] [Accepted: 12/08/2005] [Indexed: 11/18/2022] Open
Abstract
Spontaneous, short-lived, focal cytosolic Ca2+ transients were found for the first time and characterized in freshly dissociated chromaffin cells from mouse. Produced by release of Ca2+ from intracellular stores and mediated by type 2 and perhaps type 3 ryanodine receptors (RyRs), these transients are quantitatively similar in magnitude and duration to Ca2+ syntillas in terminals of hypothalamic neurons, suggesting that Ca2+ syntillas are found in a variety of excitable, exocytotic cells. However, unlike hypothalamic nerve terminals, chromaffin cells do not display syntilla activation by depolarization of the plasma membrane, nor do they have type 1 RyRs. It is widely thought that focal Ca2+ transients cause "spontaneous" exocytosis, although there is no direct evidence for this view. Hence, we monitored catecholamine release amperometrically while simultaneously imaging Ca2+ syntillas, the first such simultaneous measurements. Syntillas failed to produce exocytotic events; and, conversely, spontaneous exocytotic events were not preceded by syntillas. Therefore, we suggest that a spontaneous syntilla, at least in chromaffin cells, releases Ca2+ into a cytosolic microdomain distinct from the microdomains containing docked, primed vesicles. Ryanodine (100 microM) reduced the frequency of Ca2+ syntillas by an order of magnitude but did not alter the frequency of spontaneous amperometric events, suggesting that syntillas are not involved in steps preparatory to spontaneous exocytosis. Surprisingly, ryanodine also increased the total charge of individual amperometric events by 27%, indicating that intracellular Ca2+ stores can regulate quantal size.
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Affiliation(s)
- Ronghua ZhuGe
- Department of Physiology, and Biomedical Imaging Group, University of Massachusetts Medical School, Worcester, Massachusetts 01655, USA
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39
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Kishimoto T, Kimura R, Liu TT, Nemoto T, Takahashi N, Kasai H. Vacuolar sequential exocytosis of large dense-core vesicles in adrenal medulla. EMBO J 2006; 25:673-82. [PMID: 16467850 PMCID: PMC1383564 DOI: 10.1038/sj.emboj.7600983] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/31/2005] [Accepted: 01/11/2006] [Indexed: 11/08/2022] Open
Abstract
Individual exocytic events in intact adrenal medulla were visualized by two-photon extracellular polar-tracer imaging. Exocytosis of chromaffin vesicles often occurred in a sequential manner, involving first vesicles located at the cell periphery and then those present deeper within the cytoplasm. Sequential exocytosis occurred preferentially at regions of the plasma membrane facing the intercellular space. The compound vesicles swelled to more than five times their original volume and formed vacuolar exocytic lumens as a result of expansion of intravesicular gels and their confinement within the lumen by the fusion pore and the narrow intercellular space. Such luminal swelling greatly promoted sequential exocytosis. The SNARE protein SNAP25 rapidly migrated from the plasma membrane to the membrane of fused vesicles. These data indicate that vesicles present deeper within the cytoplasm can be fusion ready like those at the cell periphery, and that swelling of exocytic lumens promotes assembly of the fusion machinery. We suggest the existence of two molecular configurations for fusion-ready states in Ca2+ -dependent exocytosis.
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Affiliation(s)
- Takuya Kishimoto
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo, Japan
- Department of Cell Physiology, National Institute for Physiological Sciences, and Graduate University of Advanced Studies (SOKENDAI), Myodaiji, Okazaki, Japan
| | - Ryoichi Kimura
- Department of Cell Physiology, National Institute for Physiological Sciences, and Graduate University of Advanced Studies (SOKENDAI), Myodaiji, Okazaki, Japan
- Department of Physiology, Hirosaki University School of Medicine, Hirosaki, Japan
| | - Ting-Ting Liu
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo, Japan
- Genome Research Center, National Yang-Ming University, Taipei, Taiwan
| | - Tomomi Nemoto
- Department of Cell Physiology, National Institute for Physiological Sciences, and Graduate University of Advanced Studies (SOKENDAI), Myodaiji, Okazaki, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi, Saitama, Japan
| | - Noriko Takahashi
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo, Japan
- Department of Cell Physiology, National Institute for Physiological Sciences, and Graduate University of Advanced Studies (SOKENDAI), Myodaiji, Okazaki, Japan
- Precursory Research for Embryonic Science and Technology (PRESTO), Japan Science and Technology Agency, Kawaguchi, Saitama, Japan
| | - Haruo Kasai
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo, Japan
- Department of Cell Physiology, National Institute for Physiological Sciences, and Graduate University of Advanced Studies (SOKENDAI), Myodaiji, Okazaki, Japan
- Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo 113-0033, Japan. Tel.: +81 3 5841 1439; Fax: +81 3 5841 1442; E-mail:
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40
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Wang CT, Bai J, Chang PY, Chapman ER, Jackson MB. Synaptotagmin-Ca2+ triggers two sequential steps in regulated exocytosis in rat PC12 cells: fusion pore opening and fusion pore dilation. J Physiol 2005; 570:295-307. [PMID: 16293646 PMCID: PMC1464313 DOI: 10.1113/jphysiol.2005.097378] [Citation(s) in RCA: 88] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Synaptotagmin I (Syt I), the putative Ca(2+) sensor in regulated exocytosis, has two Ca(2+)-binding modules, the C2A and C2B domains, and a number of putative effectors to which Syt I binds in a Ca(2+)-dependent fashion. The role of Ca(2+) binding to these domains remains unclear, as efforts to address questions about Ca(2+)-triggered effector interactions have led to conflicting results. We have studied the effects of Ca(2+) on fusion pores using amperometry to follow the exocytosis of single vesicles in real time and analyse the kinetics of fusion pore transitions. Elevating [Ca(2+)] in permeabilized cells reduced the fusion pore lifetime, indicating an action of Ca(2+) during the actual fusion process. Analysing the Ca(2+) dependence of the fusion pore lifetime, together with the frequency of pore openings and the proportion of openings that close without dilating (kiss-and-run events) enabled us to resolve exocytosis into a sequence of kinetic steps representing functional transitions in the fusion pore. Fusion pore opening and dilation were both accelerated by Ca(2+), indicating separate Ca(2+) control over each of these steps. Ca(2+) ligand mutations in either the C2A or C2B domains of Syt I reduced fusion pore opening, but had opposite actions on the rate of fusion pore closure. These studies resolve two separate and distinct Ca(2+)-triggered steps during regulated exocytosis. The C2A and C2B domains of Syt I have different actions during these steps, and these actions may be linked to their distinctive effector interactions.
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Affiliation(s)
- Chih-Tien Wang
- Department of Physiology, University of Wisconsin, Madison, 53706, USA
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41
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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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42
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Kishimoto T, Liu TT, Hatakeyama H, Nemoto T, Takahashi N, Kasai H. Sequential compound exocytosis of large dense-core vesicles in PC12 cells studied with TEPIQ (two-photon extracellular polar-tracer imaging-based quantification) analysis. J Physiol 2005; 568:905-15. [PMID: 16150797 PMCID: PMC1464190 DOI: 10.1113/jphysiol.2005.094003] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
We investigated exocytosis of PC12 cells using two-photon excitation imaging and extracellular polar tracers (TEP imaging) at the basal region of PC12 cells adjacent to the glass cover slip. TEPIQ (two-photon extracellular polar-tracer imaging-based quantification) analysis revealed that most exocytosis was mediated by large dense-core vesicles (LVs) with a mean diameter of 220 nm, and that exocytosis of LVs occurred slowly with a mean latency of approximately 7 s even though exocytosis was induced with large increases in cytosolic Ca2+ concentration by uncaging of a caged-Ca2+ compound. We also found that 97% of exocytic LVs remained poised at the plasma membrane, 72% maintained their fusion pores in an open conformation for more than 30 s, and 76% triggered sequential compound exocytosis of vesicles that were located deeper in the cytosol. Sequential compound exocytosis by PC12 cells was confirmed by electron microscopic investigation with photoconversion of diaminobenzidine by FM1-43 (a polar membrane tracer). Our data suggest that pre-stimulus docking of LVs to the plasma membrane does not necessarily hasten the fusion reaction, while docking and resulting stability of exocytic LVs facilitates sequential compound exocytosis, and thereby allowing mobilization of deep vesicles.
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Affiliation(s)
- Takuya Kishimoto
- Department of Cell Physiology, National Institute for Physiological Sciences, Myodaiji, Okazaki 444-8787, Japan
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43
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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: 77] [Impact Index Per Article: 4.1] [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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44
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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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45
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Chan SA, Polo-Parada L, Smith C. Action potential stimulation reveals an increased role for P/Q-calcium channel-dependent exocytosis in mouse adrenal tissue slices. Arch Biochem Biophys 2005; 435:65-73. [PMID: 15680908 DOI: 10.1016/j.abb.2004.12.005] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2004] [Revised: 11/22/2004] [Indexed: 11/28/2022]
Abstract
Chromaffin cells of the adrenal medulla receive cholinergic input from the splanchnic nerve. Upon sympathetic activity, chromaffin cells fire action potentials that open voltage-gated calcium channels and evoke the exocytic release of catecholamines. Catecholamines then regulate homeostatic processes such as cardiac output and vascular tone. Thus control of the Ca(2+) influx in chromaffin cells represents a target for the regulation of multiple physiological functions. Previous reports utilized square pulse depolarizations to quantify the proportional exocytic response as a function of Ca(2+) channel subtype. In this study, we use perforated patch voltage clamp and action potential waveforms to depolarize cells in situ. We analyze Ca(2+) current components under conditions that match the dynamic native cell behavior. This approach revealed a greater role for P/Q-type calcium channels in evoked exocytosis than previously reported. Thus, the P/Q-type channels represent a more important control point for the regulation of catecholamine-dependent processes than previously believed.
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Affiliation(s)
- Shyue-An Chan
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106, USA
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46
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Harkins AB, Cahill AL, Powers JF, Tischler AS, Fox AP. Deletion of the synaptic protein interaction site of the N-type (CaV2.2) calcium channel inhibits secretion in mouse pheochromocytoma cells. Proc Natl Acad Sci U S A 2004; 101:15219-24. [PMID: 15471993 PMCID: PMC524046 DOI: 10.1073/pnas.0401001101] [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: 12/17/2022] Open
Abstract
Presynaptic N-type Ca2+ channels (CaV2.2, alpha1B) are thought to bind to SNARE (SNAP-25 receptor) complex proteins through a synaptic protein interaction (synprint) site on the intracellular loop between domains II and III of the alpha1B subunit. Whether binding of syntaxin to the N-type Ca2+ channels is required for coupling Ca2+ ion influx to rapid exocytosis has been the subject of considerable investigation. In this study, we deleted the synprint site from a recombinant alpha1B Ca2+ channel subunit and transiently transfected either the wild-type alpha1B or the synprint deletion mutant into mouse pheochromocytoma (MPC) cell line 9/3L, a cell line that has the machinery required for rapid stimulated exocytosis but lacks endogenous voltage-dependent Ca2+ channels. Secretion was elicited by activation of exogenously transfected Ca2+ channel subunits. The current-voltage relationship was similar for the wild-type and mutant alpha1B-containing Ca2+ channels. Although total Ca2+ entry was slightly larger for the synprint deletion channel, compared with the wild-type channel, when Ca2+ entry was normalized to cell size and limited to cells with similar Ca2+ entry (approximately 150 x 10(6) Ca2+ ions/pF cell size), total secretion and the rate of secretion, determined by capacitance measurements, were significantly reduced in cells expressing the synprint deletion mutant channels, compared with wild-type channels. Furthermore, the amount of endocytosis was significantly reduced in cells with the alpha1B synprint deletion mutant, compared with the wild-type subunit. These results suggest that the synprint site is necessary for efficient coupling of Ca2+ influx through alpha1B-containing Ca2+ channels to exocytosis.
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Affiliation(s)
- Amy B Harkins
- Department of Pharmacological and Physiological Science, Saint Louis University School of Medicine, 1402 South Grand Boulevard, St. Louis, MO 63104, USA.
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47
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Xia S, Xu L, Bai L, Xu ZQD, Xu T. Labeling and dynamic imaging of synaptic vesicle-like microvesicles in PC12 cells using TIRFM. Brain Res 2004; 997:159-64. [PMID: 14706868 DOI: 10.1016/j.brainres.2003.10.052] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Total internal reflection fluorescence microscopy (TIRFM) was employed to study the trafficking and exocytosis of synaptic vesicle-like microvesicles (SLMVs) in PC12 cells. SLMVs were labeled with vesicular acetylcholine transporter (VAChT) tagged with enhanced green fluorescent protein (EGFP), which displayed punctuate distribution under TIRFM and confocal microscopy. Immunofluorescence analysis confirmed the colocalization of EGFP and VAChT. No significant difference was observed in the distribution or sorting of VAChT when fused either at the N- or the C-terminus. Thus, tagging with GFP does not appear to impair or change the traffic of the VAChT in PC12 cells. Under TIRFM, EGFP-labeled spots moved in a restrained fashion, which resembled that of secretory granules and underwent exocytosis upon stimulation. Together, these data indicate that EGFP-tagged VAChT can be used to explore SLMVs trafficking using TIRFM.
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Affiliation(s)
- Sheng Xia
- Institute of Biophysics and Biochemistry, Huazhong University of Science and Technology, Wuhan, Hubei, (430074), PR China
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48
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Abstract
Several caged calciums have been synthesized since 1986, and three are commercially available: DM-nitrophen, NP-EGTA, and nitr-5. Each of these caged compounds has uniquely useful properties, making the choice of which cage to use dependent on the specific experiment (i.e., the cell type and divalent cation requirements of the experiments within purview). Significantly, methods have been developed for all three cages that permit their quantitative use inside many cell types, including those with some of the most demanding of requirements for experiments with caged calcium, namely, in relating presynaptic [Ca] to postsynaptic function. The success of such experiments using DM-nitrophen and NP-EGTA suggests that caged calcium is now a mature tool for cellular physiology and neurobiology.
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Affiliation(s)
- Graham C R Ellis-Davies
- Department of Pharmacology and Physiology, Drexel University College of Medicine, Philadelphia, Pennsylvania 19102, USA
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49
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Chan SA, Smith C. Physiological stimuli evoke two forms of endocytosis in bovine chromaffin cells. J Physiol 2001; 537:871-85. [PMID: 11744761 PMCID: PMC2279013 DOI: 10.1111/j.1469-7793.2001.00871.x] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022] Open
Abstract
1. Exocytosis and endocytosis were measured following single, or trains of, simulated action potentials (sAP) in bovine adrenal chromaffin cells. Catecholamine secretion was measured by oxidative amperometry and cell membrane turnover was measured by voltage clamp cell capacitance measurements. 2. The sAPs evoked inward Na(+) and Ca(2+) currents that were statistically identical to those evoked by native action potential waveforms. On average, a single secretory granule underwent fusion following sAP stimulation. An equivalent amount of membrane was then quickly internalised (tau = 560 ms). 3. Stimulation with sAP trains revealed a biphasic relationship between cell firing rate and endocytic activity. At basal stimulus frequencies (single to 0.5 Hz) cells exhibited a robust membrane internalisation that then diminished as firing increased to intermediate levels (1.9 and 6 Hz). However at the higher stimulation rates (10 and 16 Hz) endocytic activity rebounded and was again able to effectively maintain cell surface near pre-stimulus levels. 4. Treatment with cyclosporin A and FK506, inhibitors of the phosphatase calcineurin, left endocytosis characteristics unaltered at the lower basal stimulus levels, but blocked the resurgence in endocytosis seen in control cells at higher sAP frequencies. 5. Based on these findings we propose that, under physiological electrical stimulation, chromaffin cells internalise membrane via two distinct pathways that are separable. One is prevalent at basal stimulus frequencies, is lessened with increased firing, and is insensitive to cyclosporin A and FK506. A second endocytic form is activated by increased firing frequencies, and is selectively blocked by cyclosporin A and FK506.
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Affiliation(s)
- S A Chan
- Department of Physiology and Biophysics, Case Western Reserve University, Cleveland, OH 44106-4970, USA
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50
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Henkel AW, Kang G, Kornhuber J. A common molecular machinery for exocytosis and the ‘kiss-and-run’ mechanism in chromaffin cells is controlled by phosphorylation. J Cell Sci 2001; 114:4613-20. [PMID: 11792825 DOI: 10.1242/jcs.114.24.4613] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Exocytosis and ‘kiss-and-run’ secretion coexist in chromaffin cells. Our findings suggest that these mechanisms are closely related, based on their common molecular machinery. Here we present a model that describes how chromaffin cells regulate catecholamine release by switching the mode of secretion between the two pathways, a process controlled by phosphorylation. Stimulation-dependent vesicle-plasma membrane interactions in chromaffin cells were analysed by simultaneous ‘on-cell’ capacitance and conductance measurements, a technique that allows the monitoring of single vesicles. Capacitance steps represent fusions of large dense-core vesicles with the plasma membrane, whereas capacitance flickers correspond to transient connections of the vesicle lumen with the extracellular space. All these events require the presence of extracellular calcium in millimolar concentrations. ‘Kiss-and-run’ type of release is enhanced by the kinase inhibitor staurosporine, which suggests that this secretion mode is regulated by protein phosphorylation. We also observed capacitance bursts, which most probably represent ‘hot spots’ of secretion and we found that ‘kiss-and-run’ is the prevalent mechanism during these episodes. The significance of ‘kiss-and run’ for neurohormone release is even higher at physiological temperature, because up to half of all secretion events are mediated by this mechanism.
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Affiliation(s)
- A W Henkel
- Department of Psychiatry, University of Erlangen, Schwabachanlage 6, 91054 Erlangen, Germany.
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