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Tse A, Lee AK, Takahashi N, Gong A, Kasai H, Tse FW. Strong stimulation triggers full fusion exocytosis and very slow endocytosis of the small dense core granules in carotid glomus cells. J Neurogenet 2018; 32:267-278. [PMID: 30484390 DOI: 10.1080/01677063.2018.1497629] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
Chemosensory glomus cells of the carotid bodies release transmitters, including ATP and dopamine mainly via the exocytosis of small dense core granules (SDCGs, vesicular diameter of ∼100 nm). Using carbon-fiber amperometry, we showed previously that with a modest uniform elevation in cytosolic Ca2+ concentration ([Ca2+]i of ∼0.5 µM), SDCGs of rat glomus cells predominantly underwent a "kiss-and-run" mode of exocytosis. Here, we examined whether a larger [Ca2+]i rise influenced the mode of exocytosis. Activation of voltage-gated Ca2+ channels by a train of voltage-clamped depolarizations which elevated [Ca2+]i to ∼1.6 μM increased the cell membrane capacitance by ∼2.5%. At 30 s after such a stimulus, only 5% of the added membrane was retrieved. Flash photolysis of caged-Ca2+ (which elevated [Ca2+]i to ∼16 μM) increased cell membrane capacitance by ∼13%, and only ∼30% of the added membrane was retrieved at 30 s after the UV flash. When exocytosis and endocytosis were monitored using the two-photon excitation and extracellular polar tracer (TEP) imaging of FM1-43 fluorescence in conjunction with photolysis of caged Ca2+, almost uniform exocytosis was detected over the cell's entire surface and it was followed by slow endocytosis. Immunocytochemistry showed that the cytoplasmic densities of dynamin I, II and clathrin (key proteins that mediate endocytosis) in glomus cells were less than half of those in adrenal chromaffin cells, suggesting that a lower expression of endocytotic machinery may underlie the slow endocytosis in glomus cells. An analysis of the relative change in the signals from two fluorescent dyes that simultaneously monitored the addition of vesicular volume and plasma membrane surface area, suggested that with an intense stimulus, SDCGs of glomus cells underwent full fusion without any significant "compound" exocytosis. Therefore, during a severe hypoxic challenge, glomus granules undergo full fusion for a more complete release of transmitters.
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Affiliation(s)
- Amy Tse
- a Department of Pharmacology and Neuroscience and Metal Health Institute , University of Alberta , Edmonton , Canada
| | - Andy K Lee
- a Department of Pharmacology and Neuroscience and Metal Health Institute , University of Alberta , Edmonton , Canada
| | - Noriko Takahashi
- b Department of Physiology , Kitasato University School of Medicine , Sagamihara , Japan
| | - Alex Gong
- a Department of Pharmacology and Neuroscience and Metal Health Institute , University of Alberta , Edmonton , Canada
| | - Haruo Kasai
- c Laboratory of Structural Physiology, Center for Disease Biology and Integrative Medicine, Faculty of Medicine , The University of Tokyo , Bunkyo-ku , Japan.,d International Research Center for Neurointelligence (WPI-IRCN), UTIAS, The University of Tokyo , Bunkyo-ku , Japan
| | - Frederick W Tse
- a Department of Pharmacology and Neuroscience and Metal Health Institute , University of Alberta , Edmonton , Canada
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2
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Brännmark C, Lövfors W, Komai AM, Axelsson T, El Hachmane MF, Musovic S, Paul A, Nyman E, Olofsson CS. Mathematical modeling of white adipocyte exocytosis predicts adiponectin secretion and quantifies the rates of vesicle exo- and endocytosis. J Biol Chem 2017; 292:20032-20043. [PMID: 28972187 DOI: 10.1074/jbc.m117.801225] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/13/2017] [Revised: 09/22/2017] [Indexed: 11/06/2022] Open
Abstract
Adiponectin is a hormone secreted from white adipocytes and takes part in the regulation of several metabolic processes. Although the pathophysiological importance of adiponectin has been thoroughly investigated, the mechanisms controlling its release are only partly understood. We have recently shown that adiponectin is secreted via regulated exocytosis of adiponectin-containing vesicles, that adiponectin exocytosis is stimulated by cAMP-dependent mechanisms, and that Ca2+ and ATP augment the cAMP-triggered secretion. However, much remains to be discovered regarding the molecular and cellular regulation of adiponectin release. Here, we have used mathematical modeling to extract detailed information contained within our previously obtained high-resolution patch-clamp time-resolved capacitance recordings to produce the first model of adiponectin exocytosis/secretion that combines all mechanistic knowledge deduced from electrophysiological experimental series. This model demonstrates that our previous understanding of the role of intracellular ATP in the control of adiponectin exocytosis needs to be revised to include an additional ATP-dependent step. Validation of the model by introduction of data of secreted adiponectin yielded a very close resemblance between the simulations and experimental results. Moreover, we could show that Ca2+-dependent adiponectin endocytosis contributes to the measured capacitance signal, and we were able to predict the contribution of endocytosis to the measured exocytotic rate under different experimental conditions. In conclusion, using mathematical modeling of published and newly generated data, we have obtained estimates of adiponectin exo- and endocytosis rates, and we have predicted adiponectin secretion. We believe that our model should have multiple applications in the study of metabolic processes and hormonal control thereof.
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Affiliation(s)
- Cecilia Brännmark
- Department of Physiology/Metabolic Physiology, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at University of Gothenburg, Medicinaregatan 11, SE-405 30 Göteborg
| | - William Lövfors
- Departments of Biomedical Engineering, SE-581 83 Linköping; Mathematics, Linköping University, SE-581 83 Linköping
| | - Ali M Komai
- Department of Physiology/Metabolic Physiology, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at University of Gothenburg, Medicinaregatan 11, SE-405 30 Göteborg
| | - Tom Axelsson
- Departments of Biomedical Engineering, SE-581 83 Linköping
| | - Mickaël F El Hachmane
- Department of Physiology/Metabolic Physiology, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at University of Gothenburg, Medicinaregatan 11, SE-405 30 Göteborg
| | - Saliha Musovic
- Department of Physiology/Metabolic Physiology, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at University of Gothenburg, Medicinaregatan 11, SE-405 30 Göteborg
| | - Alexandra Paul
- Department of Biology and Biological Engineering, Chalmers University of Technology, Kemivägen 10 SE-412 96 Göteborg
| | - Elin Nyman
- Departments of Biomedical Engineering, SE-581 83 Linköping; Cardiovascular and Metabolic Diseases iMed Biotech Unit, AstraZeneca R&D, 431 83 Gothenburg, Sweden.
| | - Charlotta S Olofsson
- Department of Physiology/Metabolic Physiology, Institute of Neuroscience and Physiology, The Sahlgrenska Academy at University of Gothenburg, Medicinaregatan 11, SE-405 30 Göteborg.
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Yue HY, Bieberich E, Xu J. Promotion of endocytosis efficiency through an ATP-independent mechanism at rat calyx of Held terminals. J Physiol 2017; 595:5265-5284. [PMID: 28555839 DOI: 10.1113/jp274275] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/04/2017] [Accepted: 05/15/2017] [Indexed: 01/14/2023] Open
Abstract
KEY POINTS At rat calyx of Held terminals, ATP was required not only for slow endocytosis, but also for rapid phase of compensatory endocytosis. An ATP-independent form of endocytosis was recruited to accelerate membrane retrieval at increased activity and temperature. ATP-independent endocytosis primarily involved retrieval of pre-existing membrane, which depended on Ca2+ and the activity of neutral sphingomyelinase but not clathrin-coated pit maturation. ATP-independent endocytosis represents a non-canonical mechanism that can efficiently retrieve membrane at physiological conditions without competing for the limited ATP at elevated neuronal activity. ABSTRACT Neurotransmission relies on membrane endocytosis to maintain vesicle supply and membrane stability. Endocytosis has been generally recognized as a major ATP-dependent function, which efficiently retrieves more membrane at elevated neuronal activity when ATP consumption within nerve terminals increases drastically. This paradox raises the interesting question of whether increased activity recruits ATP-independent mechanism(s) to accelerate endocytosis at the same time as preserving ATP availability for other tasks. To address this issue, we studied ATP requirement in three typical forms of endocytosis at rat calyx of Held terminals by whole-cell membrane capacitance measurements. At room temperature, blocking ATP hydrolysis effectively abolished slow endocytosis and rapid endocytosis but only partially inhibited excess endocytosis following intense stimulation. The ATP-independent endocytosis occurred at calyces from postnatal days 8-15, suggesting its existence before and after hearing onset. This endocytosis was not affected by a reduction of exocytosis using the light chain of botulinum toxin C, nor by block of clathrin-coat maturation. It was abolished by EGTA, which preferentially blocked endocytosis of retrievable membrane pre-existing at the surface, and was impaired by oxidation of cholesterol and inhibition of neutral sphingomyelinase. ATP-independent endocytosis became more significant at 34-35°C, and recovered membrane by an amount that, on average, was close to exocytosis. The results of the present study suggest that activity and temperature recruit ATP-independent endocytosis of pre-existing membrane (in addition to ATP-dependent endocytosis) to efficiently retrieve membrane at nerve terminals. This less understood endocytosis represents a non-canonical mechanism regulated by lipids such as cholesterol and sphingomyelinase.
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Affiliation(s)
- Hai-Yuan Yue
- Departments of Neuroscience and Regenerative Medicine, Augusta University, USA
| | - Erhard Bieberich
- Departments of Neuroscience and Regenerative Medicine, Augusta University, USA
| | - Jianhua Xu
- Departments of Neuroscience and Regenerative Medicine, Augusta University, USA.,Department of Neurology, Medical College of Georgia, Augusta University, USA
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Yue HY, Xu J. Cholesterol regulates multiple forms of vesicle endocytosis at a mammalian central synapse. J Neurochem 2015; 134:247-60. [PMID: 25893258 DOI: 10.1111/jnc.13129] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/11/2014] [Revised: 03/01/2015] [Accepted: 03/31/2015] [Indexed: 01/10/2023]
Abstract
Endocytosis in synapses sustains neurotransmission by recycling vesicle membrane and maintaining the homeostasis of synaptic membrane. A role of membrane cholesterol in synaptic endocytosis remains controversial because of conflicting observations, technical limitations in previous studies, and potential interference from non-specific effects after cholesterol manipulation. Furthermore, it remains unclear whether cholesterol participates in distinct forms of endocytosis that function under different activity levels. In this study, applying the whole-cell membrane capacitance measurement to monitor endocytosis in real time at the rat calyx of Held terminals, we found that disrupting cholesterol with dialysis of cholesterol oxidase or methyl-β-cyclodextrin impaired three different forms of endocytosis, including slow endocytosis, rapid endocytosis, and endocytosis of the retrievable membrane that exists at the surface before stimulation. The effects were observed when disruption of cholesterol was mild enough not to change Ca(2+) channel current or vesicle exocytosis, indicative of stringent cholesterol requirement in synaptic endocytosis. Extracting cholesterol with high concentrations of methyl-β-cyclodextrin reduced exocytosis, mainly by decreasing the readily releasable pool and the vesicle replenishment after readily releasable pool depletion. Our study suggests that cholesterol is an important, universal regulator in multiple forms of vesicle endocytosis at mammalian central synapses.
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Affiliation(s)
- Hai-Yuan Yue
- Department of Neuroscience and Regenerative Medicine, Georgia Regents University, Augusta, Georgia, USA
| | - Jianhua Xu
- Department of Neuroscience and Regenerative Medicine, Georgia Regents University, Augusta, Georgia, USA.,Department of Neurology, Medical College of Georgia, Georgia Regents University, Augusta, Georgia, USA
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Bulk-like endocytosis plays an important role in the recycling of insulin granules in pancreatic beta cells. Protein Cell 2012; 3:618-26. [PMID: 22729398 DOI: 10.1007/s13238-012-2938-0] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2012] [Accepted: 05/10/2012] [Indexed: 10/28/2022] Open
Abstract
Although bulk endocytosis has been found in a number of neuronal and endocrine cells, the molecular mechanism and physiological function of bulk endocytosis remain elusive. In pancreatic beta cells, we have observed bulk-like endocytosis evoked both by flash photolysis and trains of depolarization. Bulk-like endocytosis is a clathrin-independent process that is facilitated by enhanced extracellular Ca(2+) entry and suppressed by the inhibition of dynamin function. Moreover, defects in bulk-like endocytosis are accompanied by hyperinsulinemia in primary beta cells dissociated from diabetic KKAy mice, which suggests that bulk-like endocytosis plays an important role in maintaining the exo-endocytosis balance and beta cell secretory capability.
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6
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Tse A, Lee AK, Tse FW. Ca2+ signaling and exocytosis in pituitary corticotropes. Cell Calcium 2012; 51:253-9. [PMID: 22225940 DOI: 10.1016/j.ceca.2011.12.007] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2011] [Revised: 12/08/2011] [Accepted: 12/10/2011] [Indexed: 10/14/2022]
Abstract
The secretion of adrenocorticotrophin (ACTH) from corticotropes is a key component in the endocrine response to stress. The resting potential of corticotropes is set by the basal activities of TWIK-related K(+) (TREK)-1 channel. Corticotrophin-releasing hormone (CRH), the major ACTH secretagogue, closes the background TREK-1 channels via the cAMP-dependent pathway, resulting in depolarization and a sustained rise in cytosolic [Ca(2+)] ([Ca(2+)](i)). By contrast, arginine vasopressin and norepinephrine evoke Ca(2+) release from the inositol trisphosphate (IP(3))-sensitive store, resulting in the activation of small conductance Ca(2+)-activated K(+) channels and hyperpolarization. Following [Ca(2+)](i) rise, cytosolic Ca(2+) is taken into the mitochondria via the uniporter. Mitochondrial inhibition slows the decay of the Ca(2+) signal and enhances the depolarization-triggered exocytotic response. Both voltage-gated Ca(2+) channel activation and intracellular Ca(2+) release generate spatial Ca(2+) gradients near the exocytic sites such that the local [Ca(2+)] is ~3-fold higher than the average [Ca(2+)](i). The stimulation of mitochondrial metabolism during the agonist-induced Ca(2+) signal and the robust endocytosis following stimulated exocytosis enable corticotropes to maintain sustained secretion during the diurnal ACTH surge. Arachidonic acid (AA) which is generated during CRH stimulation activates TREK-1 channels and causes hyperpolarization. Thus, corticotropes may regulate ACTH release via an autocrine feedback mechanism.
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Affiliation(s)
- Amy Tse
- Department of Pharmacology, University of Alberta, Edmonton, Alberta, Canada.
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He Z, Fan J, Kang L, Lu J, Xue Y, Xu P, Xu T, Chen L. Ca2+Triggers a Novel Clathrin-Independent but Actin-Dependent Fast Endocytosis in Pancreatic Beta Cells. Traffic 2008; 9:910-23. [DOI: 10.1111/j.1600-0854.2008.00730.x] [Citation(s) in RCA: 33] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Onganer PU, Djamgoz MBA, Whyte K, Greenfield SA. An acetylcholinesterase-derived peptide inhibits endocytic membrane activity in a human metastatic breast cancer cell line. Biochim Biophys Acta Gen Subj 2006; 1760:415-20. [PMID: 16469451 DOI: 10.1016/j.bbagen.2005.12.016] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/15/2005] [Revised: 12/14/2005] [Accepted: 12/19/2005] [Indexed: 12/11/2022]
Abstract
Acetylcholinesterase (AChE) is well established as having non-cholinergic functions and is also expressed in breast tumours where its function(s) is not known. Recently, a candidate peptide sequence towards the C-terminal of the AChE molecule has been identified, as the salient site remote from normal catalysis in neurons, and possibly other cells. The main aim of this study was to explore the possibility that 'AChE-peptide' might also affect human breast cancer cells. Uptake of the non-cytotoxic tracer horseradish peroxidase (HRP) was used as an index of endocytosis, a key component of the metastatic cascade, representing exocytosis/secretory membrane activity and/or plasma membrane protein turnover. AChE-peptide had no affect on the weakly metastatic MCF-7 human breast cancer cell line. By contrast, application of AChE-peptide to the strongly metastatic MDA-MB-231 cells resulted in a dose-dependent inhibition of HRP uptake; treatment with a scrambled variant of the peptide of comparable amino acid length was ineffective. The action of AChE-peptide was suppressed by lowering the extracellular Ca2+ concentration and co-applying a selective antagonist of alpha7, but not alpha4/beta2, nicotinic receptor. The results suggest that AChE-peptide has a novel, selective bioactivity on breast cancer cells and can potentiate metastatic cell behaviour.
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Affiliation(s)
- Pinar U Onganer
- Neuroscience Solutions to Cancer Research Group, Division of Cell and Molecular Biology, Sir Alexander Fleming Building, Imperial College London, South Kensington Campus, London SW7 2AZ, UK
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Bauer RA, Overlease RL, Lieber JL, Angleson JK. Retention and stimulus-dependent recycling of dense core vesicle content in neuroendocrine cells. J Cell Sci 2004; 117:2193-202. [PMID: 15126621 DOI: 10.1242/jcs.01093] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/30/2022] Open
Abstract
We have used fluorescence imaging of individual exocytic events in combination with immunogold electron microscopy and FM1-43 photoconversion to study the stimulus-dependent recycling of dense core vesicle content in isolated rat pituitary lactotrophs. Secretory stimulation with high external [K+] resulted in 100 exocytic sites per cell that were labeled by extracellular antibodies against the peptide hormone prolactin. Morphological analysis demonstrated that the prolactin was retained and internalized in intact dense cores. Vesicles containing non-secreted, internalized prolactin did not colocalize with DiI-LDL that had been chased into lysosomes but did transiently colocalize with internalized transferrin. The recycling vesicles also trafficked through a syntaxin 6-positive compartment but not the TGN38-positive trans-Golgi. Recycling vesicles, which returned to the cell surface in a slow basal manner, could also be stimulated to undergo exocytosis with a high release probability during subsequent exocytic stimulation with external K+. These studies suggest a functional role for recycling vesicles that retain prolactin.
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Affiliation(s)
- Roslyn A Bauer
- Department of Biological Sciences, University of Denver, Denver, CO 80208, USA
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Mycielska ME, Fraser SP, Szatkowski M, Djamgoz MBA. Contribution of functional voltage-gated Na+ channel expression to cell behaviors involved in the metastatic cascade in rat prostate cancer: II. Secretory membrane activity. J Cell Physiol 2003; 195:461-9. [PMID: 12704656 DOI: 10.1002/jcp.10265] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The secretory membrane activities of two rat prostate cancer cell lines of markedly different metastatic potential, and corresponding electrophysiological characteristics, were studied in a comparative approach. In particular, voltage-gated Na(+) channels (VGSCs) were expressed in the strongly metastatic MAT-LyLu but not in the closely related, but weakly metastatic, AT-2 cells. Uptake and release of the non-cytotoxic marker horseradish peroxidase (HRP) were used as indices of general endocytotic and exocytotic membrane activity, respectively. The amount of tracer present in a given experimental condition was quantified by light microscopic digital imaging. The uptake of HRP was an active process, abolished completely by incubating the cells at low temperature (5 degrees C) and suppressed by disrupting the cytoskeleton. Interestingly, the extent of HRP uptake into the strongly metastatic MAT-LyLu cells was almost twice that into the weakly metastatic AT-2 cells. Vesicular uptake of HRP occurred in a fast followed by a slow phase; these appeared to correspond to cytoplasmic and perinuclear pools, respectively. Importantly, the overall quantitative difference in the uptake disappeared in the presence of 1 microM tetrodotoxin which significantly reduced the uptake of HRP into the MAT-LyLu cells. There was no effect on the AT-2 cells, consistent with functional VGSC expression occurring selectively in the former. A similar effect was observed in Na(+)-free medium. The uptake was partially dependent upon extracellular Ca(2+) but was not affected by raising the extracellular K(+) concentration. We suggest that functional VGSC expression could potentiate prostate cancer cells' metastatic ability by enhancing their secretory membrane activity.
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Affiliation(s)
- M E Mycielska
- Department of Biological Sciences, Sir Alexander Fleming Building, Imperial College of Science, Technology, and Medicine, London, United Kingdom
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Feng D, Crane K, Rozenvayn N, Dvorak AM, Flaumenhaft R. Subcellular distribution of 3 functional platelet SNARE proteins: human cellubrevin, SNAP-23, and syntaxin 2. Blood 2002; 99:4006-14. [PMID: 12010801 DOI: 10.1182/blood.v99.11.4006] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Morphologic studies have demonstrated a process by which alpha-granule contents are released from platelets. Studies aimed at defining the molecular mechanisms of this release have demonstrated that SNARE proteins are required for alpha-granule secretion. These observations raise the possibility that morphologic features of alpha-granule secretion may be influenced by the subcellular distribution of SNARE proteins in the platelet. To evaluate this possibility, we analyzed the subcellular distribution of 3 functional platelet SNARE proteins-human cellubrevin, SNAP-23, and syntaxin 2. Exposure of streptolysin O-permeabilized platelets to antihuman cellubrevin antibody inhibited Ca(++)-induced alpha-granule secretion by approximately 50%. Inhibition of alpha-granule secretion by antihuman cellubrevin was reversed by a blocking peptide. Syntaxin 2 and SNAP-23 have previously been demonstrated to mediate platelet granule secretion. The subcellular localization of the 3 SNARE proteins was determined by ultrastructural studies, using a pre-embedding immunonanogold method, and by immunoblot analysis of subcellular fractions. Immunonanogold localization demonstrated that approximately 80% of human cellubrevin in resting platelets was localized to platelet granule membranes. In contrast, SNAP-23 localized predominantly to plasma membrane, whereas syntaxin 2 was more evenly distributed among membranes of alpha-granules, the open canalicular system, and plasma membrane. Thus, each of these SNARE proteins has a distinct subcellular distribution in platelets, and each of these membrane compartments demonstrates a unique SNARE protein composition. This distribution provides a basis for several characteristics of alpha-granule secretion that include homotypic alpha-granule fusion and the fusion of alpha-granules with the open canalicular system and plasma membrane.
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Affiliation(s)
- Dian Feng
- Department of Medicine, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA 02215, USA
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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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