We thank the NINDS Intramural Research Programs (ZIA NS003009-13 and ZIA NS003105-08) for supporting this work.

<ol>
	<li>Wu, L. G., Hamid, E., Shin, W., Chiang, H. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exocytosis+and+endocytosis:+modes,+functions,+and+coupling+mechanisms.">Exocytosis and endocytosis: modes, functions, and coupling mechanisms.</a> Annual Review of Physiology. 76, 301-331 (2014).</li><li>Chang, C. W., Chiang, C. W., Jackson, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Fusion+pores+and+their+control+of+neurotransmitter+and+hormone+release.">Fusion pores and their control of neurotransmitter and hormone release.</a> Journal of General Physiology. 149 (3), 301-322 (2017).</li><li>Harrison, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Viral+membrane+fusion.">Viral membrane fusion.</a> Nature Structural &amp; Molecular Biology. 15 (7), 690-698 (2008).</li><li>Zhao, W. D., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Hemi-fused+structure+mediates+and+controls+fusion+and+fission+in+live+cells.">Hemi-fused structure mediates and controls fusion and fission in live cells.</a> Nature. 534 (7608), 548-552 (2016).</li><li>Klyachko, V. A., Jackson, M. B. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Capacitance+steps+and+fusion+pores+of+small+and+large-dense-core+vesicles+in+nerve+terminals.">Capacitance steps and fusion pores of small and large-dense-core vesicles in nerve terminals.</a> Nature. 418 (6893), 89-92 (2002).</li><li>Albillos, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+exocytotic+event+in+chromaffin+cells+revealed+by+patch+amperometry.">The exocytotic event in chromaffin cells revealed by patch amperometry.</a> Nature. 389 (6650), 509-512 (1997).</li><li>He, L., Wu, X. S., Mohan, R., Wu, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+modes+of+fusion+pore+opening+revealed+by+cell-attached+recordings+at+a+synapse.">Two modes of fusion pore opening revealed by cell-attached recordings at a synapse.</a> Nature. 444 (7115), 102-105 (2006).</li><li>Chiang, H. C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Post-fusion+structural+changes+and+their+roles+in+exocytosis+and+endocytosis+of+dense-core+vesicles.">Post-fusion structural changes and their roles in exocytosis and endocytosis of dense-core vesicles.</a> Nature Communications. 5, 3356 (2014).</li><li>Sharma, S., Lindau, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+fusion+pore,+60+years+after+the+first+cartoon.">The fusion pore, 60 years after the first cartoon.</a> Federation of European Biochemical Societies Letters. 592 (21), 3542-3562 (2018).</li><li>Jorgacevski, J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Munc18-1+tuning+of+vesicle+merger+and+fusion+pore+properties.">Munc18-1 tuning of vesicle merger and fusion pore properties.</a> Journal of Neuroscience. 31 (24), 9055-9066 (2011).</li><li>Rituper, B., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vesicle+cholesterol+controls+exocytotic+fusion+pore.">Vesicle cholesterol controls exocytotic fusion pore.</a> Cell Calcium. 101, 102503 (2021).</li><li>Gucek, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Dominant+negative+SNARE+peptides+stabilize+the+fusion+pore+in+a+narrow,+release-unproductive+state.">Dominant negative SNARE peptides stabilize the fusion pore in a narrow, release-unproductive state.</a> Cellular and Molecular Life Sciences. 73 (19), 3719-3731 (2016).</li><li>Grabner, C. P., Moser, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Individual+synaptic+vesicles+mediate+stimulated+exocytosis+from+cochlear+inner+hair+cells.">Individual synaptic vesicles mediate stimulated exocytosis from cochlear inner hair cells.</a> Proceedings of the National Academy of Sciences of the United States of America. 115 (50), 12811-12816 (2018).</li><li>Wen, P. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Actin+dynamics+provides+membrane+tension+to+merge+fusing+vesicles+into+the+plasma+membrane.">Actin dynamics provides membrane tension to merge fusing vesicles into the plasma membrane.</a> Nature Communications. 7, 12604 (2016).</li><li>Shin, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualization+of+Membrane+Pore+in+Live+Cells+Reveals+a+Dynamic-Pore+Theory+Governing+Fusion+and+Endocytosis.">Visualization of Membrane Pore in Live Cells Reveals a Dynamic-Pore Theory Governing Fusion and Endocytosis.</a> Cell. 173 (4), 934-945 (2018).</li><li>Shin, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vesicle+Shrinking+and+Enlargement+Play+Opposing+Roles+in+the+Release+of+Exocytotic+Contents.">Vesicle Shrinking and Enlargement Play Opposing Roles in the Release of Exocytotic Contents.</a> Cell Reports. 30 (2), 421-431 (2020).</li><li>Ge, L., Shin, W., Wu, L. -. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Visualizing+sequential+compound+fusion+and+kiss-and-run+in+live+excitable+cells.">Visualizing sequential compound fusion and kiss-and-run in live excitable cells.</a> bioRxiv. , (2021).</li><li>Zhang, Q., Li, Y., Tsien, R. W. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+dynamic+control+of+kiss-and-run+and+vesicular+reuse+probed+with+single+nanoparticles.">The dynamic control of kiss-and-run and vesicular reuse probed with single nanoparticles.</a> Science. 323 (5920), 1448-1453 (2009).</li><li>He, L., Wu, X. S., Mohan, R., Wu, L. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Two+modes+of+fusion+pore+opening+revealed+by+cell-attached+recordings+at+a+synapse.">Two modes of fusion pore opening revealed by cell-attached recordings at a synapse.</a> Nature. 444 (7115), 102-105 (2006).</li><li>Androutsellis-Theotokis, A., Rubin de Celis, M. F., Ehrhart-Bornstein, M., Bornstein, S. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Common+features+between+chromaffin+and+neural+progenitor+cells.">Common features between chromaffin and neural progenitor cells.</a> Molecular Psychiatry. 17 (4), 351 (2012).</li><li>Bornstein, S. R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Chromaffin+cells:+the+peripheral+brain.">Chromaffin cells: the peripheral brain.</a> Molecular Psychiatry. 17 (4), 354-358 (2012).</li><li>Park, Y., Kim, K. T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Short-term+plasticity+of+small+synaptic+vesicle+(SSV)+and+large+dense-core+vesicle+(LDCV)+exocytosis.">Short-term plasticity of small synaptic vesicle (SSV) and large dense-core vesicle (LDCV) exocytosis.</a> Cellular Signalling. 21 (10), 1465-1470 (2009).</li><li>Thahouly, T., Niedergang, F., Vitale, N., Gasman, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Bovine+Chromaffin+Cells:+Culture+and+Fluorescence+Assay+for+Secretion.">Bovine Chromaffin Cells: Culture and Fluorescence Assay for Secretion.</a> Exocytosis and Endocytosis. Methods in Molecular Biology. 2233, (2021).</li><li>Shin, W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Preformed+Omega-profile+closure+and+kiss-and-run+mediate+endocytosis+and+diverse+endocytic+modes+in+neuroendocrine+chromaffin+cells.">Preformed Omega-profile closure and kiss-and-run mediate endocytosis and diverse endocytic modes in neuroendocrine chromaffin cells.</a> Neuron. 109 (19), 3119-3134 (2021).</li><li>O'Connor, D. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Primary+culture+of+bovine+chromaffin+cells.">Primary culture of bovine chromaffin cells.</a> Nature Protocols. 2 (5), 1248-1253 (2007).</li><li>Wu, X. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Membrane+Tension+Inhibits+Rapid+and+Slow+Endocytosis+in+Secretory+Cells.">Membrane Tension Inhibits Rapid and Slow Endocytosis in Secretory Cells.</a> Biophysical Journal. 113 (11), 2406-2414 (2017).</li><li>Revelo, N. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+new+probe+for+super-resolution+imaging+of+membranes+elucidates+trafficking+pathways.">A new probe for super-resolution imaging of membranes elucidates trafficking pathways.</a> Journal of Cell Biology. 205 (4), 591-606 (2014).</li><li>Gao, J., Liao, J., Yang, G. -. Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=CAAX-box+protein,+prenylation+process+and+carcinogenesis.">CAAX-box protein, prenylation process and carcinogenesis.</a> American journal of translational research. 1 (3), 312-325 (2009).</li><li>Schermelleh, L., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Super-resolution+microscopy+demystified.">Super-resolution microscopy demystified.</a> Nature Cell Biology. 21 (1), 72-84 (2019).</li><li>Ceccarelli, B., Hurlbut, W. P., Mauro, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Depletion+of+vesicles+from+frog+neuromuscular+junctions+by+prolonged+tetanic+stimulation.">Depletion of vesicles from frog neuromuscular junctions by prolonged tetanic stimulation.</a> Journal of Cell Biology. 54 (1), 30-38 (1972).</li><li>Rust, M. J., Bates, M., Zhuang, X. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Sub-diffraction-limit+imaging+by+stochastic+optical+reconstruction+microscopy+(STORM).">Sub-diffraction-limit imaging by stochastic optical reconstruction microscopy (STORM).</a> Nature Methods. 3 (10), 793-795 (2006).</li><li>Betzig, E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+intracellular+fluorescent+proteins+at+nanometer+resolution.">Imaging intracellular fluorescent proteins at nanometer resolution.</a> Science. 313 (5793), 1642-1645 (2006).</li><li>Fish, K. N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Total+internal+reflection+fluorescence+(TIRF)+microscopy.">Total internal reflection fluorescence (TIRF) microscopy.</a> Current Protocols in Cytometry. , 18 (2009).</li><li>Schmidt, R., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=MINFLUX+nanometer-scale+3D+imaging+and+microsecond-range+tracking+on+a+common+fluorescence+microscope.">MINFLUX nanometer-scale 3D imaging and microsecond-range tracking on a common fluorescence microscope.</a> Nature Communications. 12 (1), 1478 (2021).</li></ol>

The authors have no conflicts of interest to disclose.

A confocal microscopic imaging method is described to detect the dynamics of fusion pore and transmitter release, as well as three fusion modes, close-fusion, stay-fusion, and shrink-fusion in bovine adrenal chromaffin cells4,24. An electrophysiological method to depolarize the cell and thereby evoke exo- and endocytosis is described. Systematic confocal image processing provides information about different modes of pore behaviors for fusion and fission events.</...

Membrane fusion mediates many biological functions, including synaptic transmission, blood glucose homeostasis, immune response, and viral entry1,2,3. Exocytosis, involving vesicle fusion at the plasma membrane, releases neurotransmitters and hormones to achieve many important functions, such as neuronal network activities. Fusion opens a pore to release vesicular contents, after which the pore may close to retrieve the fusing vesicle, which is termed kiss-and-run1,4. Both irreversible and reversible fusion pore opening can be measured with cell-attached capacitance recordings combined with fusion pore conductance recordings of single vesicle fusion.
This is often interpreted as reflecting full-collapse fusion, involving dilation of the fusion until flattening of the fusing vesicle, and kiss-and-run, involving fusion pore opening and closure, respectively5,6,7,8,9,10,11,12,13. Recent confocal and stimulated emission depletion (STED) imaging studies in chromaffin cells directly observed fusion pore opening and closure (kiss-and-run, also called close-fusion), fusion pore opening that maintains an &#937;-shape with an open pore for a long time, termed stay-fusion, and shrinking of the fusing vesicle until it complete merges with the plasma membrane, which replaces full-collapse fusion for merging fusing vesicles with the plasma membrane4,8,14,15,16,17.
In neurons, fusion pore opening and closure have been detected with imaging showing the release of quantum dots preloaded in vesicles that are larger than the fusion pore and with fusion pore conductance measurements at the release face of nerve terminals5,18,19. Adrenal chromaffin cells are widely used as a model for the study of exo- and endocytosis20,21. Although chromaffin cells contain large dense-core vesicles, whereas synapses contain small synaptic vesicles, the exocytosis and endocytosis proteins in chromaffin cells and synapses are quite analogous10,11,12,20,21,22,23.
Here, a method is described to measure these three fusion modes using a confocal imaging method combined with electrophysiology in bovine adrenal chromaffin cells (Figure 1). This method involves loading of fluorescent false neurotransmitters (FFN511) into vesicles to detect exocytosis; addition of Atto 655 (A655) in the bath solution to fill the fusion-generated &#937;-shape profile, and labeling of the plasma membrane with the PH domain of phospholipase C &#948; (PH), which binds to PtdIns(4,5)P2 at the plasma membrane8,15,24. Fusion pore dynamics can be detected through changes in different fluorescent intensities. Although described for chromaffin cells, the principle of this method described here can be applied widely to many secretory cells well beyond chromaffin cells.

<table><tbody><tr><td>Adenosine 5&#039;-triphosphate magnesium salt</td><td>Sigma</td><td>A9187-500MG</td><td>ATP for preparing internal solution</td></tr><tr><td>Atto 655</td><td>ATTO-TEC GmbH</td><td>AD 655-21</td><td>Atto dye to label bath solution</td></tr><tr><td>Basic Nucleofector for Primary Neurons</td><td>Lonza</td><td>VSPI-1003</td><td>Electroporation transfection buffer along with kit</td></tr><tr><td>Boroscilicate capillary glass pipette</td><td>Warner Instruments</td><td>64-0795</td><td>Standard wall with filament OD=2.0 mm ID=1.16 mm Length=7.5 cm</td></tr><tr><td>Bovine serum albumin</td><td>Sigma</td><td>A2153-50G</td><td>Reagent for gland digestion</td></tr><tr><td>Calcium Chloride 2 M</td><td>Quality Biological</td><td>351-130-721</td><td>Reagent for preparing bath solution</td></tr><tr><td>Cell Strainers, 100 &amp;micro;m</td><td>Falcon</td><td>352360</td><td>Material for filtering chromaffin cell suspension</td></tr><tr><td>Cesium hydroxide solution</td><td>Sigma</td><td>232041</td><td>Reagent for preparing internal solution and Cs-glutamate/Cs-EGTA stock buffer</td></tr><tr><td>Collagenase P</td><td>Sigma</td><td>11213873001</td><td>Enzyme for gland digestion</td></tr><tr><td>Coverslip</td><td>Neuvitro</td><td>GG-14-Laminin</td><td>GG-14-Laminin, 14 mm dia.#1 thick 60 pieces Laminin coated German coverslips</td></tr><tr><td>D-(+)-Glucose</td><td>Sigma</td><td>G8270-1KG</td><td>Reagent for preparing Locke&amp;rsquo;s solution and bath solution</td></tr><tr><td>DMEM</td><td>ThermoFisher Scientific</td><td>11885092</td><td>Reagent for preparing culture medium</td></tr><tr><td>EGTA</td><td>Sigma</td><td>324626-25GM</td><td>Reagent for preparing Cs-EGTA stock buffer for bath solution</td></tr><tr><td>Electroporation and Nucleofector</td><td>Amaxa Biosystems</td><td>Nucleofector II</td><td>Transfect plasmids into cells</td></tr><tr><td>Fetal bovine serum</td><td>ThermoFisher Scientific</td><td>10082147</td><td>Reagent for preparing culture medium</td></tr><tr><td>FFN511</td><td>Abcam</td><td>ab120331</td><td>Fluorescent false neurotransmitter to label vesicles</td></tr><tr><td>Guanosine 5&#039;-triphosphate sodium salt hydrate</td><td>Sigma</td><td>G8877-250MG</td><td>GTP for preparing internal solution</td></tr><tr><td>HEPES</td><td>Sigma</td><td>H3375-500G</td><td>Reagent for preparing Locke&amp;rsquo;s solution</td></tr><tr><td>Igor Pro</td><td>WaveMetrics</td><td>Igor pro</td><td>Software for patch-clamp analysis and imaging data presentation</td></tr><tr><td>Leica Application Suite X software</td><td>Leica</td><td>LAS X software</td><td>Confocal software for imaging data collection and analysis</td></tr><tr><td>Leica TCS SP5 Confocal Laser Scanning Microscope</td><td>Leica</td><td>Leica TCS SP5</td><td>Confocal microscope for imaging data collection</td></tr><tr><td>L-Glutamic acid</td><td>Sigma</td><td>49449-100G</td><td>Reagent for preparing Cs-glutamate stock buffer for bath solution</td></tr><tr><td>Lock-in amplifier</td><td>Heka</td><td>Lock-in</td><td>Software for capacitance recording</td></tr><tr><td>Magnesium Chloride 1 M</td><td>Quality Biological</td><td>351-033-721EA</td><td>Reagent for preparing internal solution and bath solution</td></tr><tr><td>Metallized Hemacytometer Hausser Bright-Line</td><td>Hausser Scientific</td><td>3120</td><td>Counting chamber</td></tr><tr><td>Microforge</td><td>Narishige</td><td>MF-830</td><td>Polish pipettes to enhance the formation and stability of giga-ohm seals</td></tr><tr><td>Millex-GP Syringe Filter Unit, 0.22 &amp;micro;m</td><td>Millipore</td><td>SLGPR33RB</td><td>Material for glands wash and digestion</td></tr><tr><td>mNG(mNeonGreen)</td><td>Allele Biotechnology</td><td>ABP-FP-MNEONSB</td><td>Template for PH-mNeonGreen construction</td></tr><tr><td>Nylon mesh filtering screen 100 micron</td><td>EIKO filtering co</td><td>03-100/32</td><td>Material for filtering medulla suspension</td></tr><tr><td>Patch clamp EPC-10</td><td>Heka</td><td>EPC-10</td><td>Amplifier for patch-clamp data collection</td></tr><tr><td>PH-EGFP</td><td>Addgene</td><td>Plasmid #51407</td><td>Backbone for PH-mNeonGreen construction</td></tr><tr><td>Pipette puller</td><td>Sutter Instrument</td><td>P-97</td><td>Make pipettes for patch-clamp recording</td></tr><tr><td>Potassium Chloride</td><td>Sigma</td><td>P5404-500G</td><td>Reagent for preparing Locke&amp;rsquo;s solution and bath solution</td></tr><tr><td>Pulse software</td><td>Heka</td><td>Pulse</td><td>Software for patch-clamp data collection</td></tr><tr><td>Recording chamber</td><td>Warner Instruments</td><td>64-1943/QR-40LP</td><td>coverslip chamber, apply patch-clamp pipette on live cells</td></tr><tr><td>Sodium chloride</td><td>Sigma</td><td>S7653-1KG</td><td>Reagent for preparing Locke&amp;rsquo;s solution, bath solution and internal solution</td></tr><tr><td>Sodium hydroxide</td><td>Sigma</td><td>S5881-500G</td><td>Reagent for preparing Locke&amp;rsquo;s solution</td></tr><tr><td>Sodium phosphate dibasic</td><td>Sigma</td><td>S0876-500G</td><td>Reagent for preparing Locke&amp;rsquo;s solution</td></tr><tr><td>Sodium phosphate monobasic</td><td>Sigma</td><td>S8282-500G</td><td>Reagent for preparing Locke&amp;rsquo;s solution</td></tr><tr><td>Stirring hot plate</td><td>Barnsted/Thermolyne</td><td>type 10100</td><td>Heater for pipette coating with wax</td></tr><tr><td>Syringe, 30 mL</td><td>Becton Dickinson</td><td>302832</td><td>Material for glands wash and digestion</td></tr><tr><td>Tetraethylammonium chloride</td><td>Sigma</td><td>T2265-100G</td><td>TEA for preparing bath solution</td></tr><tr><td>Trypsin inhibitor</td><td>Sigma</td><td>T9253-5G</td><td>Reagent for gland digestion</td></tr><tr><td>Type F Immersion liquid</td><td>Leica</td><td>195371-10-9</td><td>Leica confocal mounting oil</td></tr></tbody></table>

confocal microscopy to measure three modes of fusion pore dynamics in adrenal chromaffin cells

Dynamic fusion pore opening and closure mediate exocytosis and endocytosis and determine their kinetics. Here, it is demonstrated in detail how confocal microscopy was used in combination with patch-clamp recording to detect three fusion modes in primary culture bovine adrenal chromaffin cells. The three fusion modes include 1) close-fusion (also called kiss-and-run), involving fusion pore opening and closure, 2) stay-fusion, involving fusion pore opening and maintaining the opened pore, and 3) shrink-fusion, involving shrinkage of the fusion-generated &#937;-shape profile until it merges completely at the plasma membrane.
To detect these fusion modes, the plasma membrane was labeled by overexpressing mNeonGreen attached with the PH domain of phospholipase C &#948; (PH-mNG), which binds to phosphatidylinositol-4,5-bisphosphate (PtdIns(4,5)P2) at the cytosol-facing leaflet of the plasma membrane; vesicles were loaded with the fluorescent false neurotransmitter FFN511 to detect vesicular content release; and Atto 655 was included in the bath solution to detect fusion pore closure. These three fluorescent probes were imaged simultaneously at ~20-90 ms per frame in live chromaffin cells to detect fusion pore opening, content release, fusion pore closure, and fusing vesicle size changes. The analysis method is described to distinguish three fusion modes from these fluorescence measurements. The method described here can, in principle, apply to many secretory cells beyond chromaffin cells.

Following the experimental procedures shown in Figure 1 and Figure 2, chromaffin cells from bovine adrenal glands were transfected with PH-mNG to label the plasma membrane; A655 was added to the bath solution to detect fusion pore closure; and fluorescent false neurotransmitter FFN511 was loaded in vesicles for detection of release. Next, XY-plane confocal timelapse imaging of FFN511, PH-mNG, and A655 was performed every 20-90 ms at the cell bottom (Z-focal plan...

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Confocal Microscopy to Measure Three Modes of Fusion Pore Dynamics in Adrenal Chromaffin Cells

This protocol describes a confocal imaging technique to detect three fusion modes in bovine adrenal chromaffin cells. These fusion modes include 1) close-fusion (also called kiss-and-run), involving fusion pore opening and closure, 2) stay-fusion, involving fusion pore opening and maintaining the opened pore, and 3) shrink-fusion, involving fused vesicle shrinkage.

Dynamic fusion pore opening and closure mediate exocytosis and endocytosis and determine their kinetics. Here, it is demonstrated in detail how confocal ...

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2.1K Views.  National Institute of Neurological Disorders and Stroke. This protocol describes a confocal imaging technique to detect three fusion modes in bovine adrenal chromaffin cells. These fusion modes include 1) close-fusion (also called kiss-and-run), involving fusion pore opening and closure, 2) stay-fusion, involving fusion pore opening and maintaining the opened pore, and 3) shrink-fusion, involving fused vesicle shrinkage. 

Video: Confocal Microscopy to Measure Three Modes of Fusion Pore Dynamics in Adrenal Chromaffin Cells

Methods for Cell-attached Capacitance Measurements in Mouse Adrenal Chromaffin Cell

Neuronal transmission is an integral part of cellular communication within the brain. Depolarization of the presynaptic membrane leads to vesicle fusion known as exocytosis that mediates synaptic transmission. Subsequent retrieval of synaptic vesicles is necessary to generate new neurotransmitter-filled vesicles in a process identified as endocytosis. During exocytosis, fusing vesicle membranes will result in an increase in surface area and subsequent endocytosis results in a decrease in the surface area. Here, our lab demonstrates a basic introduction to cell-attached capacitance recordings of single endocytic events in the mouse adrenal chromaffin cell. This type of electrical recording is useful for high-resolution recordings of exocytosis and endocytosis at the single vesicle level. While this technique can detect both vesicle exocytosis and endocytosis, the focus of our lab is vesicle endocytosis. Moreover, this technique allows us to analyze the kinetics of single endocytic events. Here the methods for mouse adrenal gland tissue dissection, chromaffin cell culture, basic cell-attached techniques, and subsequent examples of individual traces measuring singular endocytic event are described.

After exocytosis, fused plasma membrane is retrieved through a process known as endocytosis. This mechanism reforms new synaptic vesicles for the next round of release. Individual endocytic events are captured and analyzed through the use of the cell-attached capacitance recordings in mouse adrenal chromaffin cells.

Neuronal transmission is an integral part of cellular communication within the brain. Depolarization of the presynaptic membrane leads to vesicle fusion ...

Isolation, Fixation, and Immunofluorescence Imaging of Mouse Adrenal Glands

Immunofluorescence is a well-established technique for detection of antigens in tissues with the employment of fluorochrome-conjugated antibodies and has a broad spectrum of applications. Detection of antigens allows for characterization and identification of multiple cell types. Located above the kidneys and encapsulated by a layer of mesenchymal cells, the adrenal gland is an endocrine organ composed by two different tissues with different embryological origins, the mesonephric intermediate mesoderm-derived outer cortex and the neural crest-derived inner medulla. The adrenal cortex secretes steroids (i.e., mineralocorticoids, glucocorticoids, sex hormones), whereas the adrenal medulla produces catecholamines (i.e., adrenaline, noradrenaline). While conducting adrenal research, it is important to be able to distinguish unique cells with different functions. Here we provide a protocol developed in our laboratory that describes a series of sequential steps required for obtaining immunofluorescence staining to characterize the cell types of the adrenal gland. We focus first on the dissection of the mouse adrenal glands, the microscopic removal of periadrenal fat followed by the fixation, processing and paraffin embedding of the tissue. We then describe sectioning of the tissue blocks with a rotary microtome. Lastly, we detail a protocol for immunofluorescent staining of adrenal glands that we have developed to minimize both non-specific antibody binding and autofluorescence in order to achieve an optimal signal.

Here we present a method to isolate adrenal glands from mice, fix the tissues, section them, and perform immunofluorescence staining.

Immunofluorescence is a well-established technique for detection of antigens in tissues with the employment of fluorochrome-conjugated antibodies and has ...

Immunology and Infection

Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis

Amperometry recording of cells subjected to osmotic shock show that secretory cells respond to this physical stress by reducing the exocytosis activity and the amount of neurotransmitter released from vesicles in single exocytosis events. It has been suggested that the reduction in neurotransmitters expelled is due to alterations in membrane biophysical properties when cells shrink in response to osmotic stress and with assumptions made that secretory vesicles in the cell cytoplasm are not affected by extracellular osmotic stress. Amperometry recording of exocytosis monitors what is released from cells the moment a vesicle fuses with the plasma membrane, but does not provide information on the vesicle content before the vesicle fusion is triggered. Therefore, by combining amperometry recording with other complementary analytical methods that are capable of characterizing the secretory vesicles before exocytosis at cells is triggered offers a broader overview for examining how secretory vesicles and the exocytosis process are affected by osmotic shock. We here describe how complementing amperometry recording with intracellular electrochemical cytometry and transmission electron microscopy (TEM) imaging can be used to characterize alterations in secretory vesicles size and neurotransmitter content at chromaffin cells in relation to exocytosis activity before and after exposure to osmotic stress. By linking the quantitative information gained from experiments using all three analytical methods, conclusions were previously made that secretory vesicles respond to extracellular osmotic stress by shrinking in size and reducing the vesicle quantal size to maintain a constant vesicle neurotransmitter concentration. Hence, this gives some clarification regarding why vesicles, in response to osmotic stress, reduce the amount neurotransmitters released during exocytosis release. The amperometric recordings here indicate this is a reversible process and that vesicle after osmotic shock are refilled with neurotransmitters when placed cells are reverted into an isotonic environment.

Osmotic stress affects exocytosis and the amount of neurotransmitter released during this process. We demonstrate how combining electrochemical methods together with transmission electron microscopy can be used to study the effect of extracellular osmotic pressure on exocytosis activity, vesicle quantal size, and the amount of neurotransmitter released during exocytosis.

Amperometry recording of cells subjected to osmotic shock show that secretory cells respond to this physical stress by reducing the exocytosis activity ...

A Faster, High Resolution, mtPA-GFP-based Mitochondrial Fusion Assay Acquiring Kinetic Data of Multiple Cells in Parallel Using Confocal Microscopy

Mitochondrial fusion plays an essential role in mitochondrial calcium homeostasis, bioenergetics, autophagy and quality control. Fusion is quantified in living cells by photo-conversion of matrix targeted photoactivatable GFP (mtPAGFP) in a subset of mitochondria. The rate at which the photoconverted molecules equilibrate across the entire mitochondrial population is used as a measure of fusion activity. Thus far measurements were performed using a single cell time lapse approach, quantifying the equilibration in one cell over an hour. Here, we scale up and automate a previously published live cell method based on using mtPAGFP and a low concentration of TMRE (15 nm). This method involves photoactivating a small portion of the mitochondrial network, collecting highly resolved stacks of confocal sections every 15 min for 1 hour, and quantifying the change in signal intensity. Depending on several factors such as ease of finding PAGFP expressing cells, and the signal of the photoactivated regions, it is possible to collect around 10 cells within the 15 min intervals. This provides a significant improvement in the time efficiency of this assay while maintaining the highly resolved subcellular quantification as well as the kinetic parameters necessary to capture the detail of mitochondrial behavior in its native cytoarchitectural environment.
Mitochondrial dynamics play a role in many cellular processes including respiration, calcium regulation, and apoptosis1,2,3,13. The structure of the mitochondrial network affects the function of mitochondria, and the way they interact with the rest of the cell. Undergoing constant division and fusion, mitochondrial networks attain various shapes ranging from highly fused networks, to being more fragmented. Interestingly, Alzheimer's disease, Parkinson's disease, Charcot Marie Tooth 2A, and dominant optic atrophy have been correlated with altered mitochondrial morphology, namely fragmented networks4,10,13. Often times, upon fragmentation, mitochondria become depolarized, and upon accumulation this leads to impaired cell function18. Mitochondrial fission has been shown to signal a cell to progress toward apoptosis. It can also provide a mechanism by which to separate depolarized and inactive mitochondria to keep the bulk of the network robust14. Fusion of mitochondria, on the other hand, leads to sharing of matrix proteins, solutes, mtDNA and the electrochemical gradient, and also seems to prevent progression to apoptosis9. How fission and fusion of mitochondria affects cell homeostasis and ultimately the functioning of the organism needs further understanding, and therefore the continuous development and optimization of how to gather information on these phenomena is necessary.
Existing mitochondrial fusion assays have revealed various insights into mitochondrial physiology, each having its own advantages. The hybrid PEG fusion assay7, mixes two populations of differently labeled cells (mtRFP and mtYFP), and analyzes the amount of mixing and colocalization of fluorophores in fused, multinucleated, cells. Although this method has yielded valuable information, not all cell types can fuse, and the conditions under which fusion is stimulated involves the use of toxic drugs that likely affect the normal fusion process. More recently, a cell free technique has been devised, using isolated mitochondria to observe fusion events based on a luciferase assay1,5. Two human cell lines are targeted with either the amino or a carboxy terminal part of Renilla luciferase along with a leucine zipper to ensure dimerization upon mixing. Mitochondria are isolated from each cell line, and fused. The fusion reaction can occur without the cytosol under physiological conditions in the presence of energy, appropriate temperature and inner mitochondrial membrane potential. Interestingly, the cytosol was found to modulate the extent of fusion, demonstrating that cell signaling regulates the fusion process 4,5. This assay will be very useful for high throughput screening to identify components of the fusion machinery and also pharmacological compounds that may affect mitochondrial dynamics. However, more detailed whole cell mitochondrial assays will be needed to complement this in vitro assay to observe these events within a cellular environment.
A technique for monitoring whole-cell mitochondrial dynamics has been in use for some time and is based on a mitochondrially-targeted photoactivatable GFP (mtPAGFP)6,11. Upon expression of the mtPAGFP, a small portion of the mitochondrial network is photoactivated (10-20%), and the spread of the signal to the rest of the mitochondrial network is recorded every 15 minutes for 1 hour using time lapse confocal imaging. Each fusion event leads to a dilution of signal intensity, enabling quantification of the fusion rate. Although fusion and fission are continuously occurring in cells, this technique only monitors fusion as fission does not lead to a dilution of the PAGFP signal6. Co-labeling with low levels of TMRE (7-15 nM in INS1 cells) allows quantification of the membrane potential of mitochondria. When mitochondria are hyperpolarized they uptake more TMRE, and when they depolarize they lose the TMRE dye. Mitochondria that depolarize no longer have a sufficient membrane potential and tend not to fuse as efficiently if at all. Therefore, active fusing mitochondria can be tracked with these low levels of TMRE9,15. Accumulation of depolarized mitochondria that lack a TMRE signal may be a sign of phototoxicity or cell death. Higher concentrations of TMRE render mitochondria very sensitive to laser light, and therefore great care must be taken to avoid overlabeling with TMRE. If the effect of depolarization of mitochondria is the topic of interest, a technique using slightly higher levels of TMRE and more intense laser light can be used to depolarize mitochondria in a controlled fashion (Mitra and Lippincott-Schwartz, 2010). To ensure that toxicity due to TMRE is not an issue, we suggest exposing loaded cells (3-15 nM TMRE) to the imaging parameters that will be used in the assay (perhaps 7 stacks of 6 optical sections in a row), and assessing cell health after 2 hours. If the mitochondria appear too fragmented and cells are dying, other mitochondrial markers, such as dsRED or Mitotracker red could be used instead of TMRE.
The mtPAGFP method has revealed details about mitochondrial network behavior that could not be visualized using other methods. For example, we now know that mitochondrial fusion can be full or transient, where matrix content can mix without changing the overall network morphology. Additionally, we know that the probability of fusion is independent of contact duration and organelle dimension, is influenced by organelle motility, membrane potential and history of previous fusion activity8,15,16,17.
In this manuscript, we describe a methodology for scaling up the previously published protocol using mtPAGFP and 15nM TMRE8 in order to examine multiple cells at a time and improve the time efficiency of data collection without sacrificing the subcellular resolution. This has been made possible by the use of an automated microscope stage, and programmable image acquisition software. Zen software from Zeiss allows the user to mark and track several designated cells expressing mtPAGFP. Each of these cells can be photoactivated in a particular region of interest, and stacks of confocal slices can be monitored for mtPAGFP signal as well as TMRE at specified intervals. Other confocal systems could be used to perform this protocol provided there is an automated stage that is programmable, an incubator with CO2, and a means by which to photoactivate the PAGFP; either a multiphoton laser, or a 405 nm diode laser.

Mitochondrial fusion was measured by tracking the equilibration of photoconverted matrix-targeted GFP across the mitochondrial network over time. Thus far, only one cell could be subjected to an hour long kinetic analysis at a time. We present a method that simultaneously measures multiple cells, thereby speeding up the data collection process.

Mitochondrial fusion plays an essential role in mitochondrial calcium homeostasis, bioenergetics, autophagy and quality control. Fusion is quantified in ...

Biology

An Analytical Tool that Quantifies Cellular Morphology Changes from Three-dimensional Fluorescence Images

The most common software analysis tools available for measuring fluorescence images are for two-dimensional (2D) data that rely on manual settings for inclusion and exclusion of data points, and computer-aided pattern recognition to support the interpretation and findings of the analysis. It has become increasingly important to be able to measure fluorescence images constructed from three-dimensional (3D) datasets in order to be able to capture the complexity of cellular dynamics and understand the basis of cellular plasticity within biological systems. Sophisticated microscopy instruments have permitted the visualization of 3D fluorescence images through the acquisition of multispectral fluorescence images and powerful analytical software that reconstructs the images from confocal stacks that then provide a 3D representation of the collected 2D images. Advanced design-based stereology methods have progressed from the approximation and assumptions of the original model-based stereology1 even in complex tissue sections2. Despite these scientific advances in microscopy, a need remains for an automated analytic method that fully exploits the intrinsic 3D data to allow for the analysis and quantification of the complex changes in cell morphology, protein localization and receptor trafficking. 
Current techniques available to quantify fluorescence images include Meta-Morph (Molecular Devices, Sunnyvale, CA) and Image J (NIH) which provide manual analysis. Imaris (Andor Technology, Belfast, Northern Ireland) software provides the feature MeasurementPro, which allows the manual creation of measurement points that can be placed in a volume image or drawn on a series of 2D slices to create a 3D object. This method is useful for single-click point measurements to measure a line distance between two objects or to create a polygon that encloses a region of interest, but it is difficult to apply to complex cellular network structures. Filament Tracer (Andor) allows automatic detection of the 3D neuronal filament-like however, this module has been developed to measure defined structures such as neurons, which are comprised of dendrites, axons and spines (tree-like structure). This module has been ingeniously utilized to make morphological measurements to non-neuronal cells3, however, the output data provide information of an extended cellular network by using a software that depends on a defined cell shape rather than being an amorphous-shaped cellular model. To overcome the issue of analyzing amorphous-shaped cells and making the software more suitable to a biological application, Imaris developed Imaris Cell. This was a scientific project with the Eidgen&ouml;ssische Technische Hochschule, which has been developed to calculate the relationship between cells and organelles. While the software enables the detection of biological constraints, by forcing one nucleus per cell and using cell membranes to segment cells, it cannot be utilized to analyze fluorescence data that are not continuous because ideally it builds cell surface without void spaces. To our knowledge, at present no user-modifiable automated approach that provides morphometric information from 3D fluorescence images has been developed that achieves cellular spatial information of an undefined shape (Figure 1). 
We have developed an analytical platform using the Imaris core software module and Imaris XT interfaced to MATLAB (Mat Works, Inc.). These tools allow the 3D measurement of cells without a pre-defined shape and with inconsistent fluorescence network components. Furthermore, this method will allow researchers who have extended expertise in biological systems, but not familiarity to computer applications, to perform quantification of morphological changes in cell dynamics.

We developed a software platform that utilizes Imaris Neuroscience, ImarisXT and MATLAB to measure the changes in morphology of an undefined shape taken from three-dimensional confocal fluorescence of single cells. This novel approach can be used to quantify changes in cell shape following receptor activation and therefore represents a possible additional tool for drug discovery.

The most common software analysis tools available for measuring fluorescence images are for two-dimensional (2D) data that rely on manual settings for ...

Ex Vivo Imaging of Cell-specific Calcium Signaling at the Tripartite Synapse of the Mouse Diaphragm

The electrical activity of cells in tissues can be monitored by electrophysiological techniques, but these are usually limited to the analysis of individual cells. Since an increase of intracellular calcium (Ca2+) in the cytosol often occurs because of the electrical activity, or in response to a myriad of other stimuli, this process can be monitored by the imaging of cells loaded with fluorescent calcium-sensitive dyes.&#160; However, it is difficult to image this response in an individual cell type within whole tissue because these dyes are taken up by all cell types within the tissue. In contrast, genetically encoded calcium indicators (GECIs) can be expressed by an individual cell type and fluoresce in response to an increase of intracellular Ca2+, thus permitting the imaging of Ca2+ signaling in entire populations of individual cell types. Here, we apply the use of the GECIs GCaMP3/6 to the mouse neuromuscular junction, a tripartite synapse between motor neurons, skeletal muscle, and terminal/perisynaptic Schwann cells. We demonstrate the utility of this technique in classic ex vivo tissue preparations. Using an optical splitter, we perform dual-wavelength imaging of dynamic Ca2+ signals and a static label of the neuromuscular junction (NMJ) in an approach that could be easily adapted to monitor two cell-specific GECI or genetically encoded voltage indicators (GEVI) simultaneously. Finally, we discuss the routines used to capture spatial maps of fluorescence intensity. Together, these optical, transgenic, and analytic techniques can be employed to study the biological activity of distinct cell subpopulations at the NMJ in a wide variety of contexts.

Ex Vivo Imaging of Cell-specific Calcium Signaling at the Tripartite Synapse of the Mouse Diaphragm

Here we present a protocol to image calcium signaling in populations of individual cell types at the murine neuromuscular junction.

The electrical activity of cells in tissues can be monitored by electrophysiological techniques, but these are usually limited to the analysis of ...

Imaging the Human Immunological Synapse

The purpose of the method is to generate an immunological synapse (IS), an example of cell-to-cell conjugation formed by an antigen-presenting cell (APC) and an effector helper T lymphocyte (Th) cell, and to record the images corresponding to the first stages of the IS formation and the subsequent trafficking events (occurring both in the APC and in the Th cell). These events will eventually lead to polarized secretion at the IS. In this protocol, Jurkat cells challenged with Staphylococcus enterotoxin E (SEE)-pulsed Raji cells as a cell synapse model was used, because of the closeness of this experimental system to the biological reality (Th cell-APC synaptic conjugates). The approach presented here involves cell-to-cell conjugation, time-lapse acquisition, wide-field fluorescence microscopy (WFFM) followed by image processing (post-acquisition deconvolution). This improves the signal-to-noise ratio (SNR) of the images, enhances the temporal resolution, allows the synchronized acquisition of several fluorochromes in emerging synaptic conjugates and decreases fluorescence bleaching. In addition, the protocol is well matched with the end point cell fixation protocols (paraformaldehyde, acetone or methanol), which would allow further immunofluorescence staining and analyses. This protocol is also compatible with laser scanning confocal microscopy (LSCM) and other state-of-the-art microscopy techniques. As a main caveat, only those T cell-APC boundaries (called IS interfaces) that were at the right 90&#176; angle to the focus plane along the Z-axis could be properly imaged and analyzed. Other experimental models exist that simplify imaging in the Z dimension and the following image analyses, but these approaches do not emulate the complex, irregular surface of an APC, and may promote non-physiological interactions in the IS. Thus, the experimental approach used here is suitable to reproduce and to confront some biological complexities occurring at the IS.

This protocol images both the immunological synapse formation and the subsequent polarized secretory traffic towards the immunological synapse. Cellular conjugates were formed between a superantigen-pulsed Raji cell (acting as an antigen-presenting cell) and a Jurkat clone (acting as an effector helper T lymphocyte).

The purpose of the method is to generate an immunological synapse (IS), an example of cell-to-cell conjugation formed by an antigen-presenting cell (APC) ...

Preparation of Pancreatic Acinar Cells for the Purpose of Calcium Imaging, Cell Injury Measurements, and Adenoviral Infection

The pancreatic acinar cell is the main parenchymal cell of the exocrine pancreas and plays a primary role in the secretion of pancreatic enzymes into the pancreatic duct. It is also the site for the initiation of pancreatitis. Here we describe how acinar cells are isolated from whole pancreas tissue and intracellular calcium signals are measured. In addition, we describe the techniques of transfecting these cells with adenoviral constructs, and subsequently measuring the leakage of lactate dehydrogenase, a marker of cell injury, during conditions that induce acinar cell injury in vitro. These techniques provide a powerful tool to characterize acinar cell physiology and pathology.

We describe a reproducible method of preparing mouse pancreatic acinar cells from a mouse for the purpose of examining acinar cell calcium signals and cellular injury with physiologically and pathologically relevant stimuli. A method for adenoviral infection of these cells is also provided.

The pancreatic acinar  cell is the main parenchymal cell of the exocrine pancreas and plays a primary  role in the secretion of pancreatic enzymes into ...

Intravital Microscopy for Imaging Subcellular Structures in Live Mice Expressing Fluorescent Proteins

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, we use the salivary glands of live mice since they provide several advantages. First, they can be easily exposed to enable access to the optics, and stabilized to facilitate the reduction of the motion artifacts due to heartbeat and respiration. This significantly facilitates imaging and tracking small subcellular structures. Second, most of the cell populations of the salivary glands are accessible from the surface of the organ. This permits the use of confocal microscopy that has a higher spatial resolution than other techniques that have been used for in vivo imaging, such as two-photon microscopy. Finally, salivary glands can be easily manipulated pharmacologically and genetically, thus providing a robust system to investigate biological processes at a molecular level.
In this study we focus on a protocol designed to follow the kinetics of the exocytosis of secretory granules in acinar cells and the dynamics of the apical plasma membrane where the secretory granules fuse upon stimulation of the beta-adrenergic receptors. Specifically, we used a transgenic mouse that co-expresses cytosolic GFP and a membrane-targeted peptide fused with the fluorescent protein tandem-Tomato. However, the procedures that we used to stabilize and image the salivary glands can be extended to other mouse models and coupled to other approaches to label in vivo cellular components, enabling the visualization of various subcellular structures, such as endosomes, lysosomes, mitochondria, and the actin cytoskeleton.

Intravital microscopy is a powerful tool that enables imaging various biological processes in live animals. In this article, we present a detailed method for imaging the dynamics of subcellular structures, such as the secretory granules, in the salivary glands of live mice.

Here we describe a procedure to image subcellular structures in live rodents that is based on the use of confocal intravital microscopy. As a model organ, ...

Imaging Plasma Membrane Deformations With pTIRFM

To gain novel insights into the dynamics of exocytosis, our group focuses on the changes in lipid bilayer shape that must be precisely regulated during the fusion of vesicle and plasma membranes. These rapid and localized changes are achieved by dynamic interactions between lipids and specialized proteins that control membrane curvature. The absence of such interactions would not only have devastating consequences for vesicle fusion, but a host of other cellular functions that involve control of membrane shape. In recent years, the identity of a number of proteins with membrane-shaping properties has been determined. What remains missing is a roadmap of when, where, and how they act as fusion and content release progress.
Our understanding of the molecular events that enable membrane remodeling has historically been limited by a lack of analytical methods that are sensitive to membrane curvature or have the temporal resolution to track rapid changes. PTIRFM satisfies both of these criteria. We discuss how pTIRFM is implemented to visualize and interpret rapid, submicron changes in the orientation of chromaffin cell membranes during dense core vesicle (DCV) fusion. The chromaffin cells we use are isolated from bovine adrenal glands. The membrane is stained with a lipophilic carbocyanine dye,1,1&#39;-dioctadecyl-3,3,3&#39;,3&#39;-tetramethylindodicarbocyanine, 4-chlorobenzenesulfonate, or&#160;diD. DiD intercalates in the membrane plane with a &#34;fixed&#34; orientation and is therefore sensitive to the polarization of the evanescent field. The diD-stained cell membrane is sequentially excited with orthogonal polarizations of a 561&#160;nm laser (p-pol, s-pol). A 488&#160;nm laser is used to visualize vesicle constituents and time the moment of fusion. Exocytosis is triggered by locally perfusing cells with a depolarizing KCl solution. Analysis is performed offline using custom-written software to understand how diD emission intensity changes relate to fusion pore dilation.

Polarization-based Total Internal Reflection Fluorescence Microscopy (pTIRFM) enables real-time detection of cell membrane dynamics. This article describes the implementation of pTIRFM for the study of membrane remodeling during regulated exocytosis. The technique is generalizable to other processes in cell biology that directly or indirectly involve changes in membrane shape.

To gain novel insights into the dynamics of exocytosis, our group focuses on the changes in lipid bilayer shape that must be precisely regulated during ...

Confocal Microscopy to Measure Three Modes of Fusion Pore Dynamics in Adrenal Chromaffin Cells

Summary

Explore More Videos

Methods for Cell-attached Capacitance Measurements in Mouse Adrenal Chromaffin Cell

Isolation, Fixation, and Immunofluorescence Imaging of Mouse Adrenal Glands

Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis

A Faster, High Resolution, mtPA-GFP-based Mitochondrial Fusion Assay Acquiring Kinetic Data of Multiple Cells in Parallel Using Confocal Microscopy

An Analytical Tool that Quantifies Cellular Morphology Changes from Three-dimensional Fluorescence Images

Ex Vivo Imaging of Cell-specific Calcium Signaling at the Tripartite Synapse of the Mouse Diaphragm

Imaging the Human Immunological Synapse

Preparation of Pancreatic Acinar Cells for the Purpose of Calcium Imaging, Cell Injury Measurements, and Adenoviral Infection

Intravital Microscopy for Imaging Subcellular Structures in Live Mice Expressing Fluorescent Proteins

Imaging Plasma Membrane Deformations With pTIRFM