Name: impact of intracardiac neurons on cardiac electrophysiology and arrhythmogenesis in an ex vivo langendorff system
Uploaded: 2018-05-22T14:00:00
Description: Watch this Scientific Journal Video about Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System at JoVE.com

The authors would like to thank Hartwig Wieboldt for his excellent technical assistance, and the UKE Microscopy Imaging Facility (Umif) of the University Medical Center Hamburg-Eppendorf for providing microscopes and support. This research was funded bythe F&#246;rderverein des Universit&#228;ren Herzzentrums Hamburg e.V. and by the DZHK (German Centre for Cardiovascular Research) [FKZ 81Z4710141].

All procedures involving animals were approved by the local authorities of the State of Hamburg, the University of Hamburg Animal Care and Use Committees.
1. Preparation of the Langendorff Apparatus
NOTE: A commercially available Langendorff perfusion system is used.
<ol>
	<li>Prepare a modified Krebs-Henseleit solution (119 mM of sodium chloride, 25 mM of sodium bicarbonate, 4.6 mM of potassium chloride, 1.2 mM of potassium phosphate monobasic, 1.1 mM of magnesiu...

<ol>
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In this manuscript, the well-known Langendorff ex vivo heart perfusion system is presented as a tool to study the impact of intracardiac neurons on cardiac electrophysiology and arrhythmogenesis by using different mapping and stimulation techniques including endocardial and epicardial approaches.
Several parts of the protocol are crucial for the setup. First, it is important to use a preparation technique in which the atrial fat pads stay intact or are removed quickly without injuring...

The Langendorff ex vivo heart perfusion system continues to be a relevant tool for performing a broad spectrum of physiological, biochemical, morphological, and pharmacological studies in centrally denervated hearts1,2,3,4,5 since its invention in the late 19th century6. To date, this system is still widely used for various topics (e.g., ischemia reperfusion) or to study cardiac pharmacological effects7,8, and is a basic tool in cardiovascular research. The longevity of this method results from several advantages (e.g., measurements are performed without the influence of the central nervous system or other organs, systemic circulation, or circulating hormones). If needed, pharmaceuticals can be added in a controlled manner to the perfusion buffer or applied to specific structures directly. Experiments are reproducible, and a relatively high number of experiments can be performed in a short period of time. The (in part) open nature of the setup can make temperature regulation difficult and needs to be taken into account. Although the Langendorff system is also used in larger species9, smaller animals are primarily used as the experimental setup is less complex, and a greater biological variability (e.g., transgenic mouse models) can be used.
In the experimental setup of this protocol, the influence of the intracardiac autonomic nervous system on basic electrophysiological parameters, ventricular arrhythmogenesis, epicardial conduction, and cyclic adenosine monophosphate (cAMP) dynamics is evaluated. A large number of intracardiac ganglia, which are mainly located in the atrial fat pads and are now well known to control cardiac electrophysiology independent from central neural control, are either left intact or manually removed with careful mechanical dissection. A pharmacological modulation of the autonomic nervous system is performed either globally by adding pharmaceuticals to the perfusion buffer or locally by targeted modulation of the atrial ganglia. After the experiments, the hearts are well suited for an immunohistological assessment as all blood cells have been removed due to the continuous perfusion, which can increase the quality of staining.
The overall goal of the described techniques is to offer novel perspectives for detailed studies regarding the impact of the autonomic nervous system on cardiac electrophysiology and arrhythmogenesis in the mouse heart. A reason to use this technique is that it is possible to study and alter the autonomic nervous system without the impact of the central nervous system. One major advantage is the easy employment of pharmacological experiments, in which potential pro- or antiarrhythmic properties of old and new agents can be tested. In addition, transgenic and knockout mouse models of various cardiac diseases are available to investigate the mechanisms underlying arrhythmias, heart failure, or metabolic diseases. This approach has enhanced our understanding of how the autonomic nervous system on the atrial level can impact ventricular cardiac electrophysiology and the induction of arrhythmias.

<table>
	<tbody>
		<tr>
			<td>Sodium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>S3014</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Sodium hydrogencarbonate</td>
			<td>Sigma-Aldrich</td>
			<td>401676</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Potassium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>P5405</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Potassium phosphate monobasic</td>
			<td>Sigma-Aldrich</td>
			<td>P5655</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Magnesium sulfate heptahydrate</td>
			<td>Sigma-Aldrich</td>
			<td>M1880</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Calcium chloride dihydrate</td>
			<td>Sigma-Aldrich</td>
			<td>C7902</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Sigma-Aldrich</td>
			<td>G5767</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Sodium pyruvate bioXtra</td>
			<td>Sigma-Aldrich</td>
			<td>P8574</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Carbogen (95% O2 / 5% CO2)</td>
			<td colspan="2">SOL-Group, TMG Technische und Medizinische Gas GmbH, Krefeld, Gersthofen, Germany</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Sterile filter steritop-GP 0.22</td>
			<td>EMD Millipore</td>
			<td>SCGPT05RE</td>
			<td>Modified Krebs-Henleit solution</td>
		</tr>
		<tr>
			<td>Atropine sulfate</td>
			<td>Sigma-Aldrich</td>
			<td>A0257</td>
			<td>Neuromodulation</td>
		</tr>
		<tr>
			<td>Hexamethonium chloride</td>
			<td>Sigma-Aldrich</td>
			<td>H2138</td>
			<td>Neuromodulation</td>
		</tr>
		<tr>
			<td>Nicotine free base 98-100%</td>
			<td>Sigma-Aldrich</td>
			<td>N3876</td>
			<td>Neuromodulation</td>
		</tr>
		<tr>
			<td>Formalin solution neutral buffered 10%</td>
			<td>Sigma-Aldrich</td>
			<td>HT501128</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Tris(hydroxymethyl)aminomethane</td>
			<td>Sigma-Aldrich</td>
			<td>252859</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Methanol</td>
			<td>Sigma-Aldrich</td>
			<td>34860</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Hydrogen peroxide solution 30% (w/w) in H2O</td>
			<td>Merck, KGA, Darmstadt, Germany</td>
			<td>H1009</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Dimethyl sulfoxide</td>
			<td>Merck, KGA, Darmstadt, Germany</td>
			<td>D8418</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Phosphate-buffered saline tablets</td>
			<td>Gibco / Invitrogen</td>
			<td>18912-014</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Triton-x-100</td>
			<td>Sigma-Aldrich</td>
			<td>T8787</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Albumin bovine fraction V</td>
			<td>Biomol, Hamburg, Germany</td>
			<td>11924.03</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Chicken anti neurofilament</td>
			<td>EMD Millipore</td>
			<td>AB5539</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Rabbit anti tyrosine hydroxylase</td>
			<td>EMD Millipore</td>
			<td>AB152</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Goat anti choline acetyltransferase</td>
			<td>EMD Millipore</td>
			<td>AP144P</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Donkey &#945; rabbit IgG Alexa 488</td>
			<td>Thermo Fisher Scientific</td>
			<td>A21206</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Donkey &#945; goat IgG Alexa 568</td>
			<td>Thermo Fisher Scientific</td>
			<td>A11057</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Donkey &#945; chicken IgY Alexa 647</td>
			<td>Merck, KGA, Darmstadt, Germany</td>
			<td>AP194SA6</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Biotin-conjugated donkey &#945; rabbit igG</td>
			<td>R&#38;D Systems</td>
			<td>AP182B</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Biotin-conjugated donkey &#945; goat igG</td>
			<td>R&#38;D Systems</td>
			<td>AP192P</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Biotin-conjugated goat &#945; chicken igY</td>
			<td>R&#38;D Systems</td>
			<td>BAD010</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>Vectashield mounting medium</td>
			<td>Vector laboratories, Burlingame, CA, USA</td>
			<td>H-1000</td>
			<td>Immunohistochemistry</td>
		</tr>
		<tr>
			<td>Vectastain ABC kit</td>
			<td>Vector laboratories, Burlingame, CA, USA</td>
			<td>PK-4000</td>
			<td>Immunohistochemistry</td>
		</tr>
		<tr>
			<td>Steady DAB/Plus</td>
			<td>Abcam plc, Cambridge, UK</td>
			<td>ab103723</td>
			<td>Whole mount staining</td>
		</tr>
		<tr>
			<td>HistoClear</td>
			<td>DiaTec, Bamberg, Germany</td>
			<td>HS2002</td>
			<td>Immunohistochemistry</td>
		</tr>
		<tr>
			<td>BisBenzimide H33342 trihydrochloride (Hoechst)</td>
			<td>Sigma-Aldrich, St. Louis, MO, USA</td>
			<td>B2261</td>
			<td>Immunohistochemistry</td>
		</tr>
		<tr>
			<td>Vectashield HardSet mounting medium</td>
			<td>Vector laboratories, Burlingame, CA, USA</td>
			<td>VEC-H-1400</td>
			<td>Immunohistochemistry</td>
		</tr>
		<tr>
			<td>Perfusion system</td>
			<td>HUGO SACHS ELEKTRONIK - HARVARD APPARATUS GmbH, March-Hugstetten, Germany</td>
			<td>&#160;73-4343</td>
			<td>Langendorff apparatus</td>
		</tr>
		<tr>
			<td>Data acquisition system and corresponding software for catheter and physiological parameter</td>
			<td>Powerlab 8/30 &#38; Labchart, ADInstruments, Dunedin, New Zealand</td>
			<td>PL3508 PowerLab 8/35</td>
			<td>Langendorff setup</td>
		</tr>
		<tr>
			<td>Octapolar catheter</td>
			<td>CIB&#8217;ER Mouse, NuMed Inc., Hopkinton, NY, USA</td>
			<td>custom</td>
			<td>Langendorff setup</td>
		</tr>
		<tr>
			<td>Stimulus generator</td>
			<td>STG4002, Multi Channel Systems, Reutlingen, Germany</td>
			<td>STG4002-160&#181;A</td>
			<td>Stimulation setup</td>
		</tr>
		<tr>
			<td>Stimulation software</td>
			<td>Multi Channel Systems, Reutlingen, Germany</td>
			<td>MC_Stimulus II</td>
			<td>Stimulation setup</td>
		</tr>
		<tr>
			<td>Data acquisition system and corresponding software for epicardial electrograms</td>
			<td>ME128-FAI-MPA-System, Multi Channel Systems, Reutlingen, Germany</td>
			<td>USB-ME128-System</td>
			<td>MEA setup</td>
		</tr>
		<tr>
			<td>Multi-electrode array</td>
			<td>MEA, EcoFlexMEA36, Multi Channel Systems, Reutlingen, Germany</td>
			<td>EcoFlexMEA36</td>
			<td>MEA setup</td>
		</tr>
		<tr>
			<td>Multi-electrode array recording software</td>
			<td>Multi Channel Systems, Reutlingen, Germany</td>
			<td>MC_Rack</td>
			<td>MEA setup</td>
		</tr>
		<tr>
			<td>Spring scissors</td>
			<td>Fine Science Tools GmbH, Heidelberg, Germany</td>
			<td>15003-08</td>
			<td>Heart Preparation</td>
		</tr>
		<tr>
			<td>Strabismus Scissors</td>
			<td>Fine Science Tools GmbH, Heidelberg, Germany</td>
			<td>14575-09</td>
			<td>Heart Preparation</td>
		</tr>
		<tr>
			<td>Mayo Scissors</td>
			<td>Fine Science Tools GmbH, Heidelberg, Germany</td>
			<td>14110-15</td>
			<td>Heart Preparation</td>
		</tr>
		<tr>
			<td>Dumont SS Forceps</td>
			<td>Fine Science Tools GmbH, Heidelberg, Germany</td>
			<td>11203-25</td>
			<td>Heart Preparation</td>
		</tr>
		<tr>
			<td>London Forceps</td>
			<td>Fine Science Tools GmbH, Heidelberg, Germany</td>
			<td>11080-02</td>
			<td>Heart Preparation</td>
		</tr>
		<tr>
			<td>Narrow Pattern Forceps</td>
			<td>Fine Science Tools GmbH, Heidelberg, Germany</td>
			<td>11003-13</td>
			<td>Heart Preparation</td>
		</tr>
		<tr>
			<td>Plastic Wrap</td>
			<td>Parafilm M, Bemis NA, based in Neenah, WI, United States</td>
			<td></td>
			<td>Consumable Materials</td>
		</tr>
		<tr>
			<td>Stereomicroscope</td>
			<td>Leica M165FC; Leica Microsystems GmbH, Wetzlar, Germany</td>
			<td></td>
			<td>FRET</td>
		</tr>
		<tr>
			<td>LED</td>
			<td>CoolLED, Andover, UK</td>
			<td>pE-100</td>
			<td>FRET</td>
		</tr>
		<tr>
			<td>DualView</td>
			<td>Photometrics, Tucson, AZ, USA</td>
			<td>DV2-SYS</td>
			<td>FRET</td>
		</tr>
		<tr>
			<td>DualView filter set</td>
			<td>Photometrics, Tucson, AZ, USA</td>
			<td>05-EM</td>
			<td>FRET</td>
		</tr>
		<tr>
			<td>optiMOS scientific CMOS camera</td>
			<td>Qimaging, Surrey, BC, Canada</td>
			<td>01-OPTIMOS-R-M-16-C</td>
			<td>FRET</td>
		</tr>
		<tr>
			<td>Imaging software &#160;</td>
			<td>Micro-Manager; Vale Lab, University of California San Francisco, CA, USA</td>
			<td></td>
			<td>FRET</td>
		</tr>
		<tr>
			<td>Analysis Software</td>
			<td>Image J software; Public Domain, NIH, USA</td>
			<td></td>
			<td>FRET</td>
		</tr>
	</tbody>
</table>

impact of intracardiac neurons on cardiac electrophysiology and arrhythmogenesis in an ex vivo langendorff system

Since its invention in the late 19th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum of physiological, biochemical, morphological, and pharmacological parameters in centrally denervated hearts. Here, we describe a setup for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cyclic adenosine monophosphate (cAMP) dynamics. The intracardiac autonomic nervous system is modulated by the mechanical dissection of atrial fat pads-in which murine ganglia are located mainly&#8212;or by the usage of global as well as targeted pharmacological interventions. An octapolar electrophysiological catheter is introduced into the right atrium and the right ventricle, and epicardial-placed multi-electrode arrays (MEA) for high-resolution mapping are used to determine cardiac electrophysiology and arrhythmogenesis. F&#246;rster resonance energy transfer (FRET) imaging is performed for the real-time monitoring of cAMP levels in different cardiac regions. Neuromorphology is studied by means of antibody-based staining of whole hearts using neuronal markers to guide the identification and modulation of specific targets of the intracardiac autonomic nervous system in the performed studies. The ex vivo Langendorff setup allows for a high number of reproducible experiments in a short time. Nevertheless, the partly open nature of the setup (e.g., during MEA measurements) makes constant temperature control difficult and should be kept to a minimum. This described method makes it possible to analyze and modulate the intracardiac autonomic nervous system in decentralized hearts.

Figure 1 shows an image of the Langendorff setup including 2 multi-electrode arrays (MEAs). Before the experiment, the intracardiac catheter is positioned close to the cannula to facilitate a quick and easy insertion in the right atrium/right ventricle and to ensure a short time period until the equilibration can start. The lower part of the chamber can be heightened (see the arrows in Figure 1) so that the chamber is fully close...

Watch this Scientific Journal Video about Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System at JoVE.com

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Here, we present a protocol for the modulation of the intracardiac autonomic nervous system and the assessment of its influence on basic electrophysiology, arrhythmogenesis, and cAMP dynamics using an ex vivo Langendorff setup.

Impact of Intracardiac Neurons on Cardiac Electrophysiology and Arrhythmogenesis in an Ex Vivo Langendorff System

Since its invention in the late 19th century, the Langendorff ex vivo heart perfusion system continues to be a relevant tool for studying a broad spectrum ...

The overall goal of this ex vivo Langendorff setup is to analyze and modulate the intracardiac autonomic nervous system and assess its influence on basic electrophysiology, arrhythmogenesis, and cAMP dynamics in decentralized hearts. The main advantage of this technique is that it allows researchers to analyze and modulate the intracardiac nervous system in decentralized hearts. Though this method can provide insight into healthy hearts, we got initial evidence that this approach can also be used to study various forms of structural heart disease.Begin by starting the water bath and placing the perfusion solution including a mixture of 95%oxygen, 5%carbon dioxide in it. Then, adjust the pump rate before attaching the heart, so that no air bubbles are left in the cannula when mounting it to the apparatus. Set the targeted perfusion pressure to 80 millimeters mercury in the general settings, and start recording.Use an electrophysiology catheter with platinum electrodes, an electrode surface of 0.5 by 0.5 millimeters, with an electrode spacing of 0.5 millimeters for the data recording and stimulation with a designated digital stimulus generator. Then, place the catheter close to the area where the heart will be positioned after the attachment to the apparatus. Next, attach the cannula quickly to the Langendorff apparatus, and ensure that there are no bubbles left in the cannula.Switch the perfusion pressure to 80 millimeters mercury, allowing a constant pressure perfusion. Insert the catheter carefully into the right atrium and right ventricle without touching or damaging the heart, and attach the catheter to the cannula with tape. Then, start the stimulation with the prepared cycle length of 100 milliseconds for an initial 20-minute equilibration period.Finally, close the chamber to allow a stable temperature. Begin by applying a programmed stimulation via the distal or proximal electrodes of the catheter at twice the atrial or ventricular pacing threshold to evaluate the electrophysiological parameters. Then, perform a programmed extrastimulation or burst pacing protocols in line with the Lambeth Conventions to evaluate the ventricular arrhythmogenesis.Next, place the multi-electrode array, MEA, in the designated area of the heart, and add the grounding to another part of the heart. Place an epicardial stimulation catheter close to the MEA, and start a constant stimulation. Finally, start recording after the confirmation of good contact of the electrodes by checking the signal quality and amplitude.Using a self-built imaging system around a stereomicroscope, begin by placing the stereomicroscope in front of the heart and adjust it for acuity. Excite the cAMP sensor with a light source, and split the emission light into donor and acceptor channels using a beam-splitter. Take images by using a scientific complementary metal-oxide-semiconductor, sCMOS, camera.Next, start the image acquisition by pushing the Multi-D Acq. Button and set up a time-lapse, which acquires an image every 10 seconds with the appropriate exposure time, depending on the strength of the fluorescent signal. Then, use the previously described and available FRET Online and FRET Online 2 plugins to split the image into two channels, select the regions of interest, and monitor the ratio tracing.During the acquisition, perfuse the heart with modified Krebs-Henseleit solution containing different substances. Then, at the end of the experiment, switch off the acquisition by pushing the Stop button and save the stack of images. Finally, analyze the FRET data offline using a dedicated analysis software that can split images into two identical sections for the donor and acceptor channels and can perform FRET analysis in multiple regions of interest.On these whole-mount stainings, parts of the autonomic nervous system are depicted. An exemplary enlargement of one immunohistochemically stained atrial ganglion demonstrates the predominantly parasympathetic cells in red, compared to less numerous sympathetic cells, which are shown in green. In representative immunohistochemical stainings, neural fibers traverse from the atria via the coronary sinus towards the posterior ventricles with sympathetic predominance.Exemplary fibers are marked by arrowheads. Here, ventricular arrhythmia susceptibility testing via the electrodes in the RV is presented. The induction of a ventricular tachycardia in hearts occurred more frequently after partial atrial denervation.Further, a global as well as local topical application of pharmaceuticals is easily possible in this experimental setup. After perfusion of the adenylyl cyclase activator to increase cAMP levels, nicotine was applied to acutely reduce cAMP levels. While attempting this procedure, it's important to keep procedure time to a minimum and at a comparable length between experiments.After watching this video, you should have a good understanding of how to investigate the impact of the intracardiac autonomic nervous system on cardiac electrophysiology, arrhythmogenesis, and cAMP dynamics in an ex vivo Langendorff setup.

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