Name: monitoring the effect of osmotic stress on secretory vesicles and exocytosis
Uploaded: 2018-02-19T13:30:00
Description: Watch this Scientific Journal Video about Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis at JoVE.com

The authors would like to thank the Swedish Research Council (349-2007-8680) for funding and Dalsj&#246;fors K&#246;tt AB (Dalsj&#246;fors, Sweden) for donation of bovine adrenal glands.

1. Cell Culture of Bovine Chromaffin Cells Isolated by Enzymatic Digestion from Adrenal Glands
<ol>
	<li>To isolate chromaffin cells collected from bovine adrenal glands, sterilize cells with 70% ethanol solution. Trim away fat and connective tissue using a scalpel. To remove blood, rinse the adrenal veins using Locke&#39;s solution (NaCl 154 mM, KCl 5.6 mM, NaHCO3 3.6 mM, hydroxyethyl piperazineethanesulfonic acid (HEPES) 5.6 mM at pH 7.4) that has been thermostated to 37 &#176;C.</li>
	<li>To digest the tissue, infla...

<ol>
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D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Role+of+Mg2++ion-activated+ATPase+and+a+pH+gradient+in+the+storage+of+catecholamines+in+synaptic+vesicles.">Role of Mg2+ ion-activated ATPase and a pH gradient in the storage of catecholamines in synaptic vesicles.</a> Biochemistry. 17 (13), 2517-2523 (1978).</li><li>Terland, O., Flatmark, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Ascorbate+as+a+natural+constituent+of+chromaffin+granules+from+the+bovine+adrenal+medulla.">Ascorbate as a natural constituent of chromaffin granules from the bovine adrenal medulla.</a> FEBS letters. 59 (1), 52-56 (1975).</li><li>Camacho, M., Machado, J. D., Montesinos, M. S., Criado, M., Borges, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Intragranular+pH+rapidly+modulates+exocytosis+in+adrenal+chromaffin+cells.">Intragranular pH rapidly modulates exocytosis in adrenal chromaffin cells.</a> J Neurochem. 96 (2), 324-334 (2006).</li><li>Jankowski, J. A., Schroeder, T. J., Ciolkowski, E. L., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+characteristics+of+quantal+secretion+of+catecholamines+from+adrenal+medullary+cells.">Temporal characteristics of quantal secretion of catecholamines from adrenal medullary cells.</a> J Biol Chem. 268 (20), 14694-14700 (1993).</li><li>Daniels, A., Williams, R., Wright, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=The+character+of+the+stored+molecules+in+chromaffin+granules+of+the+adrenal+medulla:+a+nuclear+magnetic+resonance+study.">The character of the stored molecules in chromaffin granules of the adrenal medulla: a nuclear magnetic resonance study.</a> Neurosci. 3 (6), 573-585 (1978).</li><li>Borges, R., Travis, E. R., Hochstetler, S. E., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+external+osmotic+pressure+on+vesicular+secretion+from+bovine+adrenal+medullary+cells.">Effects of external osmotic pressure on vesicular secretion from bovine adrenal medullary cells.</a> J Biol Chem. 272 (13), 8325-8331 (1997).</li><li>Troyer, K. P., Mundorf, M. L., Fries, H. E., Wightman, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Separating+vesicle+fusion+and+exocytosis+in+hypertonic+conditions.">Separating vesicle fusion and exocytosis in hypertonic conditions.</a> Ann NY Acad Sci. 971 (1), 251-253 (2002).</li><li>Brodwick, M. S., Curran, M., Edwards, C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Effects+of+osmotic+stress+on+mast+cell+vesicles+of+the+beige+mouse.">Effects of osmotic stress on mast cell vesicles of the beige mouse.</a> J Membrane Biol. 126 (2), 159-169 (1992).</li><li>Amatore, C., Arbault, S., Bonifas, I., Lemaitre, F., Verchier, Y. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Vesicular+exocytosis+under+hypotonic+conditions+shows+two+distinct+populations+of+dense+core+vesicles+in+bovine+chromaffin+cells.">Vesicular exocytosis under hypotonic conditions shows two distinct populations of dense core vesicles in bovine chromaffin cells.</a> Chem Phys Chem. 8 (4), 578-585 (2007).</li><li>Hampton, R. Y., Holz, 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=Effects+of+changes+in+osmolality+on+the+stability+and+function+of+cultured+chromaffin+cells+and+the+possible+role+of+osmotic+forces+in+exocytosis.">Effects of changes in osmolality on the stability and function of cultured chromaffin cells and the possible role of osmotic forces in exocytosis.</a> J Cell Biol. 96 (4), 1082-1088 (1983).</li><li>Troyer, K. P., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Temporal+separation+of+vesicle+release+from+vesicle+fusion+during+exocytosis.">Temporal separation of vesicle release from vesicle fusion during exocytosis.</a> J Biol Chem. 277 (32), 29101-29107 (2002).</li><li>Pihel, K., Travis, E. R., Borges, R., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Exocytotic+release+from+individual+granules+exhibits+similar+properties+at+mast+and+chromaffin+cells.">Exocytotic release from individual granules exhibits similar properties at mast and chromaffin cells.</a> Biophys J. 71 (3), 1633 (1996).</li><li>Jankowski, J. A., Finnegan, J. M., Wightman, R. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Extracellular+ionic+composition+alters+kinetics+of+vesicular+release+of+catecholamines+and+quantal+size+during+exocytosis+at+adrenal+medullary+cells.">Extracellular ionic composition alters kinetics of vesicular release of catecholamines and quantal size during exocytosis at adrenal medullary cells.</a> J Neurochem. 63 (5), 1739-1747 (1994).</li><li>Leszczyszyn, D. 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=Nicotinic+receptor-mediated+catecholamine+secretion+from+individual+chromaffin+cells.+Chemical+evidence+for+exocytosis.">Nicotinic receptor-mediated catecholamine secretion from individual chromaffin cells. Chemical evidence for exocytosis.</a> J Biol Chem. 265 (25), 14736-14737 (1990).</li><li>Wightman, 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=Temporally+resolved+catecholamine+spikes+correspond+to+single+vesicle+release+from+individual+chromaffin+cells.">Temporally resolved catecholamine spikes correspond to single vesicle release from individual chromaffin cells.</a> P Natl Acad Sci. 88 (23), 10754-10758 (1991).</li><li>Fathali, H., Dunevall, J., Majdi, S., Cans, A. -. 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We here present a protocol and the advantages of combining three complementary analytical methods to analyze secretory vesicles and the exocytosis process to gain a better understanding of how a physical force such as osmotic pressure can affect secretory vesicles and the exocytosis process in secretory cells. These methods include carbon fiber microelectrode amperometry, which is an established method for recording exocytosis activity, intracellular electrochemical cytometry, which is used to determine quantal size of v...

Chromaffin cells in adrenal glands are neuroendocrine cells that release neurotransmitter molecules into the blood stream. This occurs through a cellular process that involves the docking and fusion of neurotransmitter-filled vesicles, resulting in content release from vesicles to the extracellular space in a process called exocytosis. The neurotransmitters (adrenaline and noradrenaline) in chromaffin cells are actively transported by membrane proteins into large dense core vesicles (LDCVs) and stored at high concentrations (~0.5-1 M)1,2. Accumulation of neurotransmitters inside the LDCVs is accomplished by the affinity of catecholamine molecules to the intravesicular dense core protein matrix comprised of chromogranin proteins (~169 mg/mL)3,4,5,6, and an intravesicular cocktail solution containing key components for catecholamine loading and storage into the vesicle such as ATP (125-300 mM)7, Ca2+ (50-100 &#181;M in the solution and ~40 mM bound to the protein matrix)8, Mg2+ (5 mM)9, ascorbate (10-30 mM)10, and a pH of ~5.511,12. The LDCVs maintain an iso-osmotic condition with the cell cytoplasm (310 mOsm/kg)13, even though the theoretical solute concentration inside the vesicles sum up to more than 750 mM. The composition of the intravesicular components is not only essential for the loading and storage of catecholamines, but also for aggregation of solutes to the dense core protein matrix. This significantly reduces the osmolarity of the vesicles is significantly reduced and can affect the amount catecholamine that is released during exocytosis5,6.
Studies on the effect of extracellular osmotic pressure on the exocytosis process by amperometric recording have reported that high extracellular osmotic pressure inhibits exocytosis activity and reduces the number of neurotransmitters secreted from single vesicle compartments4,14,15,16,17,18,19. The explanations of these observations have speculated on the possible enhancement of macromolecular crowding in the cell cytoplasm inhibiting vesicle fusion events, and an alteration in membrane biophysical properties affecting the number of neurotransmitters released during exocytosis. These thoughts assumed that high extracellular osmotic stress does not affect the vesicle quantal size, which defines the number of neurotransmitter molecules stored in a vesicle compartment at prior stage of triggered exocytosis14,15,17,19,20,21. In amperometric measurements of exocytosis release in single cells, a carbon fiber disc microelectrode is placed in close contact with the cell surface, creating an experimental set up mimicking the synapse configuration, where the amperometric electrode serves as a postsynaptic detector (Figure 1)22,23. By stimulating a cell to exocytosis, one can induce neurotransmitter-filled vesicles to fuse with the cell plasma membrane and release part or the full vesicle content into the extracellular space. These neurotransmitter molecules released at the surface of the electrode can be detected electrochemically if the neurotransmitters are electroactive (e.g., catecholamines) by applying a redox potential of +700 mV vs a Ag/AgCl reference electrode. Consequently, a series of current spikes mark the detection of individual exocytosis events. From the current versus time trace in an amperometric recording, the area under each single amperometric spike represents the charge detected per exocytosis event and can be converted to the mole of neurotransmitters released, using the Faraday equation. Hence, the amperometric recordings provide quantitative information on the amount neurotransmitters expelled from single exocytosis events and report on the frequency of exocytosis events, but do not present quantitative information on the secretory vesicles content before vesicle fusion and neurotransmitter release has been initiated.
Therefore, to get a better understanding of how secretory vesicles in the cell cytoplasm respond to extracellular osmotic stress before the cell is triggered to undergo exocytosis, other complementary analytical methods can be used to enrich this information. For instance, to investigate if osmotic stress alters vesicle volume, transmission electron microscopy (TEM) imaging analysis can be used to measure the vesicle size of cells after chemical fixation. To examine if osmotic stress affects vesicle quantal size, a recently developed amperometric technique called intracellular electrochemical cytometry, can be applied for quantification of vesicle neurotransmitter content at secretory vesicles in their native state when still residing in the cytoplasm of live cells26. In the intracellular electrochemical cytometry technique, a nanotip cylindrical carbon fiber electrode is gently inserted into the cytoplasm of live cells and, by applying a +700 mV potential to this electrode (vs a Ag/AgCl reference electrode), the catecholamine content in vesicles can be quantified by the detection of a redox current spike from single vesicles colliding, adsorbing, and subsequently stochastically rupturing at the electrode surface and thereby releasing their contents against the electrode surface26. Hence, in the amperometric current versus time trace, each single vesicle rupturing event can result in a current transient and, by integrating the area of each current spike, the vesicle quantal size can be calculated using Faraday&#180;s law.
Therefore, by linking the quantitative information gained from vesicle size measurements using TEM imaging together with vesicle quantal size analysis, as recorded by intracellular electrochemical cytometry, vesicle neurotransmitter concentration can also be determined. This allows vesicle characterization when cells are exposed to different osmotic conditions and provides a better view on how vesicles may respond to extracellular osmotic stress at the stage prior to exocytosis. The results from combining these methods have shown that in the presence of extracellular high osmotic pressure, vesicles shrink and adjust their quantal size and comparing the quantitative information on the relative changes from these measurements shows that while shrinking, vesicles adjust their contents and size to maintain a constant neurotransmitter concentration24. Thus, this understanding is valuable in connecting to the observations made on neurotransmitter release in cells exposed to osmotic stress. In these protocols, we describe the use of these three complementary methodologies that allow the characterization of how secretory vesicles in their native environment respond to extracellular osmolality and the effects of this response on the exocytosis process. In addition to our previous observations regarding the effect of high osmotic pressure on exocytosis24, we present additional experiments that describe cell recovery after osmotic shock and the effect of multiple barium stimulations in chromaffin cells.

<table border="0" cellpadding="0" cellspacing="0" style="width:631px;" width="631">
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		<col />
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	</colgroup>
	<tbody>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">NaCl</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">S7653</td>
			<td style="width:167px;"></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">KCl</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">P9333</td>
			<td></td>
		</tr>
		<tr height="27">
			<td height="27" style="height:27px;width:216px;">NaHCO3</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">S5761</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">HEPES</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">H3375</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">MgCl2</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">M-2670</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Glucose</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">G8270</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Collagenase P</td>
			<td style="width:129px;">Roche, Sweden</td>
			<td style="width:119px;">11 213 857 001</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">100-&#181;M Nylon mesh</td>
			<td style="width:129px;">Fisher Sientific</td>
			<td style="width:119px;">08-771-19</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Percoll</td>
			<td style="width:129px;">Sigma Aldrich</td>
			<td style="width:119px;">P1677</td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Collagen IV coated 60 mm plastic dish</td>
			<td style="width:129px;">VWR</td>
			<td style="width:119px;">354416</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Centrifuge</td>
			<td style="width:129px;">Avanti J-20XP</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Borosilicate glass capillary</td>
			<td style="width:129px;">Sutter instrument Co., Novato, CA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Micropipette puller</td>
			<td style="width:129px;">Narishing Inc., Japan</td>
			<td style="width:119px;">PE-21</td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Epoxy solutions (A and B)</td>
			<td style="width:129px;">Epoxy technology, Billerica, MA</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Beveller</td>
			<td style="width:129px;">Narishing Inc.</td>
			<td style="width:119px;">EG-400</td>
			<td></td>
		</tr>
		<tr height="22">
			<td height="22" style="height:22px;width:216px;">Inverted Microscope</td>
			<td style="width:129px;">Olympus</td>
			<td style="width:119px;">IX81</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:216px;">Patch clamp Instrument</td>
			<td style="width:129px;">Molecular Devices, Sunnyvale, CA</td>
			<td style="width:119px;">Axopatch 200B</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:216px;">Micromanipulator</td>
			<td style="width:129px;">Burleigh Instrument Inc., USA</td>
			<td style="width:119px;">PCS-5000</td>
			<td></td>
		</tr>
		<tr height="64">
			<td height="64" style="height:64px;width:216px;">Butane Flame</td>
			<td style="width:129px;">Multiflame AB, H&#228;sselholm, Sweden</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="43">
			<td height="43" style="height:43px;width:216px;">Transmission electron microscopy</td>
			<td style="width:129px;">Omega</td>
			<td style="width:119px;">Leo 912 AB</td>
			<td></td>
		</tr>
	</tbody>
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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.

We here describe the protocol for how combining TEM imaging together with two electrochemical methodologies, carbon fiber amperometry and intracellular electrochemical cytometry, can provide information that gains a broader view alluding to the effect of extracellular osmotic pressure on secretory vesicles and the exocytosis process. By comparing representative amperometric recordings of exocytosis release at single chromaffin cells using the experimental set up (shown in Figure 1), a signif...

Watch this Scientific Journal Video about Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis at JoVE.com

Monitoring the Effect of Osmotic Stress on Secretory Vesicles and Exocytosis

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 ...

The overall goal of this combined analytical methodology is to provide information on how secretory vesicles in cells respond to a physical force, such as extracellular osmotic pressure, and how adjustments of these organelles further affect the exocytosis process. This method can help answer key questions in the neuroscience field such as, how do secretory vesicles directly respond to changes in the extracellular environment or to drug treatment? The main advantage of this approach is to monitor direct effects on vesicular content at live cells and knowing to distinguish alteration in their reh-chemical-ed release before and after exocytosis is treated.To obtain a flat disk electrode surface, place the electrode in the holder of a microgrinder and bevel each carbon fiber electrode at an angle of 45 degrees. Afterward, mark the capillary for future reference of how to locate the disk electrode surface at a 45 degree angle when placing the electrode near cells for exocytosis measurement. To perform amperometric recording at single cells, mount the freshly beveled and tested carbon fiber disk microelectrode in the electrode holder of the head stage that is used with a potentiostat.Before use, place each carbon fiber microelectrode in a test solution to monitor the study state current using cyclic voltammetry. For a cyclic voltammetry scan, apply a triangle potential waveform from negative 0.2 volts to positive 0.8 volts against a silver-silver chloride reference electrode at 100 milivolts per second to ensure good reaction kinetics. For amperometry recording of exocytosis, place the Petri dish with cultured chromaffin cells in isotonic buffer on an inverted microscope in a Faraday cage.Use a microscope heating stage to maintain a temperature of 37 degrees Celsius during the cell experiments. Next, use a low-noise patch clamp instrument to apply a constant potential of positive 700 millivolts at the working electrode. For recording exocytosis of chromaffin cells, digitalize the signal at 10 kilohertz and apply an internal low-pass Bessel filter at two kilohertz to filter the recorded signal.Note that the oval disk electrode needs to be placed flat on top of the cells and parallel to the surface of the Petri dish. Also, electrodes are beveled the same day as experiments to ensure a clean electrode surface. To stimulate the cell exocytosis, position a glass micropipette filled with five millimolar barium chloride solution at a distance of at least 20 micrometers away from the cell.Then, apply a five seconds injection pulse of five millimolar barium chloride solution on the cell's surface to stimulate the cell exocytosis. Place the stem pipette in the solution and stimulate the cell exocytosis by applying a barium injection pulse while recording the amperometric current transients for approximately three minutes. To compare the exocytotic responses in isotonic conditions to hypertonic conditions, incubate the cells for 10 minutes in hypertonic buffer solution.Thereafter, apply a barium injection pulse to stimulate exocytosis, and perform three minutes of amperometric recording. For the reversible response of cells, incubate the cells again for 10 minutes in an isotonic buffer solution. Stimulate the cells by applying a barium injection pulse and perform three minutes of recording of the exocytotic response.To fabricate the electrodes for vesicular quantal size measurements, prepare a carbon fiber electrode with a diameter of five micrometers. Under a microscope, use a scalpel to cut the carbon fiber that is extending out of the glass tip so that only 30 to 100 micrometers is left. Use a butane flame to prepare a flame-etched tip of the carbon fiber electrode.To achieve an evenly-etched, cylindrical-shaped electrode tip, hold the cylindrical-shaped carbon fiber electrode while rotating it. And place the carbon fiber extending from the glass into the blue edge of the butane flame until the tip of the carbon develops a red color. After flame etching, place the electrode under a microscope to evaluate the electrode tip.The etched electrode tip size should be about 50 to 100 nanometers in diameter. Next, insert the cylindrical nanotip microelectrode into the epoxy solution for three minutes followed by a 15 seconds dipping of the electrode tip into the acetone solution. This allow the epoxy to seal the potential gap space between the carbon fiber and the insulating gas capillary wall.While the acetone clears the epoxy off the etched carbon fiber electrode surface. To cure the epoxy, bake the electrodes in an oven overnight at 100 degrees Celsius. Before use, test the steady state current of each carbon fiber microelectrode using cyclic voltammetry.For experiments, use only electrodes that display a plateau current around 1.5 to 2.5 nanoamperes. For intracellular amperometry measurements, place the cells under the microscope and use the same experimental settings of the potentiostat. Prevent significant physical damage to the cell.Insert the nanotip cylindrical microelectrode into the cell by adding a gentle mechanical force. Just enough to push the electrode through the cell plasma membrane and into the cell cytoplasm using a micromanipulator. After insertion, and with the cell membrane sealed around the cylindrical electrode, start the amperometric recording in-situ at the live cell.At the oxidation potential applied to the electrode, vesicles adsorbed to the electrode surface and stochastically rupture. Hence, there is no need for any kind of stimulus to initiate this process. To determine the osmotic effect on vesicular quantal size, collect the intracellular cytometry measurements from a group of cells that have been incubated in isotonic and in hypertonic buffer using the experimental condition.The effect of extracellular osmolality on exocytosis activity is presented as the frequency of exocytosis events when chromaffin cells are stimulated with barium solution in isotonic, then hypertonic, and finally in isotonic conditions. This data shows an inhibition in exocytosis activity at cells experiencing osmotic stress and a partial recovery can be achieved after cells returned to an isotonic environment. The control experiment shows the frequency of exocytosis events after three consecutive barium stimulations at chromaffin cells in isotonic conditions.This shows that multiple barium stimulation within the time frame used in these experiments are causing a reduction in exocytosis activity by consecutive cell stimulation. After watching this video, you should have a good understanding of how to perform these complimentary analytical methods that allow you to compare how secretory vesicles and the exocytosis process are affected by alterations in the extracellular environment.

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