We acknowledge the support provided by the workshops and the animal facility of the Institute of Neurophysiology. This work was supported by Walter und Marga Boll- Stiftung, K&#246;ln Fortune and Deutsche Stiftung f&#252;r Herzforschung.

Animal handling has to be conform to guidelines of the local animal welfare committee and to the Directive 2010/63/EU of the European Parliament.
1. Prepare Solutions
<ol>
	<li>Prepare Tyrode&#39;s solution without Ca2+ (composition in mM): NaCl 136, KCl 5.4, NaH2PO4 0.33, MgCl2 1, glucose 10, HEPES 5, 2,3-butanedione monoxime (BDM) 30. Adjust pH to 7.4 with NaOH at 4 &#176;C.</li>
	<li>Prepare Tyrode&#39;s solution with Ca2+ (composition in mM): NaCl 136, KCl 5.4, NaH2PO4 0.33, MgCl2 1, glucose 10, HEPES 5, BDM 30, CaCl2 0.9. Adjust pH to 7.4 with NaOH at 4 &#176;C.</li>
	<li>Prepare 4% low-melt agarose: Put 0.6 g low-melt agarose in 15 mL Tyrode&#39;s solution without Ca2+. Heat the mixture in a microwave oven two times at 750 W for 10-15 s until the agarose is dissolved. Keep the solution at a constant temperature of 37 &#176;C and stir continuously.</li>
	<li>Keep Dulbecco&#39;s Modified Eagle Medium (DMEM) without serum at 37 &#176;C bubbled with carbogen (5% CO2, 95% O2).</li>
</ol>
2. Prepare the Microtome
<ol>
	<li>Switch on the microtome.</li>
	<li>Fill the outer microtome chamber with ice.</li>
	<li>Fill the inner microtome chamber with ice cold Tyrode&#39;s solution without Ca2+ and continuously oxygenate the solution with 100% O2.</li>
	<li>Place a steel blade into the blade-holder of the microtome.</li>
</ol>
3. Mouse Heart Isolation
<ol>
	<li>Inject 2,500 U Heparin subcutaneously. Wait 15 min.</li>
	<li>Sacrifice the animal by cervical dislocation.</li>
	<li>Open the chest by sternotomy.</li>
	<li>Carefully dissect the pericardium using small scissors and a forceps #5.</li>
	<li>Insert a cannula into the ascending aorta and perfuse the coronary arteries in situ with ice cold Tyrode&#39;s solution without Ca2+ until remaining blood is removed.</li>
	<li>Gently resect the heart with a forceps and scissors and transfer the heart in ice cold Tyrode&#39;s solution rode without Ca2+.</li>
	<li>Separate the atria from the ventricles with a scalpel or scissors.</li>
</ol>
4. Embedding of the Ventricles in 4% Low-melt Agarose
<ol>
	<li>Place the ventricles with the apex facing upwards in the agarose mold (Figure 1). Place the pin in the middle of the mold in the left ventricular chamber.</li>
	<li>Fill the mold with 4% low-melt agarose at 37 &#176;C, until the heart is completely covered.</li>
	<li>Place the mold on ice for faster hardening of the agarose preventing floating of the tissue.</li>
	<li>Remove the agarose block containing the ventricles from the mold with a scalpel.</li>
	<li>Turn the block upside down and fill ventricular chambers and the gap on the backside of the agarose block, which is left by the pin of the molt, with 4% low-melt agarose using a syringe with a 20 G needle.</li>
	<li>Trim the agarose block with a scalpel to achieve a flat bottom of the block and upright position of the cardiac apex.</li>
</ol>
5. Slicing the Ventricular Tissue
<ol>
	<li>Fix the block on the specimen holder of the microtome with a drop of cyanoacrylate glue. Face the cardiac apex upwards.</li>
	<li>Place the specimen holder into the inner specimen chamber of the microtome, which is filled with ice cold Tyrode without Ca2+. Completely cover the agarose block with Tyrode&#39;s solution.</li>
	<li>Prepare short-axis slices at a thickness of 150-400 &#181;m, depending on the further application (for sharp electrode recordings 150-200 &#181;m), keep vibration frequency of the blade at 60-70 Hz and move the blade forward as slowly as possible.</li>
	<li>Use a fine brush to carefully remove the remaining agarose from the slices.</li>
	<li>Gently transfer slices with a Pasteur pipette into the Tyrode&#39;s solution with 0.9 mM Ca2+ aerated with 100% O2 and store them for at least 30 min on ice to recover from the slicing procedure.</li>
	<li>Afterwards, keep slices for 30 min in DMEM at 37 &#176;C, aerated with carbogen, to wash out BDM before further use.</li>
</ol>
6. Preparing the Sharp Electrode Setup
<ol>
	<li>For pre-heating, switch on all electric devices 30 min before the recordings start.</li>
	<li>Put a 3 cm cell culture dish on the heating plate placed on the inverted microscope.</li>
	<li>Place the custom-made ring electrode (Figure 2) in the dish and connect grounding wires of the pre-amplifier and the stimulation electrode.</li>
	<li>Connect the flexible tubes of the perfusion system to the dish.</li>
	<li>Fill the reservoir of the perfusion system with DMEM, aerated with carbogen.</li>
	<li>Switch on the perfusion pump and set the perfusion rate to 2-3 mL/min.</li>
	<li>Adjust the temperature of DMEM in the dish to 37 &#176;C by regulating the flow heater and the heating plate.</li>
</ol>
7. Action Potential Recordings
<ol>
	<li>Place a ventricular slice into the DMEM filled dish.</li>
	<li>Check the structural integrity and viability (based on contractile function) of the tissue with the inverted microscope.</li>
	<li>Fill a recording glass electrode with 3 M KCL.</li>
	<li>Fill a stimulation electrode with DMEM.</li>
	<li>Place the recording electrode and the stimulation electrode on the electrode holders.</li>
	<li>Place the stimulation electrode carefully on the slice and switch on the electric stimulator. Start with a stimulation frequency of 1-2 Hz.</li>
	<li>Move the recording electrode with the micromanipulator over the intended recording position.</li>
	<li>Slowly lower the recording electrode until the tip touches the tissue.</li>
	<li>Apply a short rectangular electric pulse through the recording electrode to penetrate the cell membrane.</li>
	<li>Carefully reposition the recording electrode until a stable signal is ensured.</li>
	<li>Start recording of action potentials.</li>
</ol>

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M., Olinga, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Precision-cut+tissue+slices+as+a+tool+to+predict+metabolism+of+novel+drugs.">Precision-cut tissue slices as a tool to predict metabolism of novel drugs.</a> Expert Opin Drug Metab Toxicol. 3, 879-898 (2007).</li><li>Kim, Y. 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=Cardiopulmonary+toxicity+of+peat+wildfire+particulate+matter+and+the+predictive+utility+of+precision+cut+lung+slices.">Cardiopulmonary toxicity of peat wildfire particulate matter and the predictive utility of precision cut lung slices.</a> Part Fibre Toxicol. 11, 29 (2014).</li><li>Nembo, E. 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The authors have nothing to declare.

Ventricular slices enable electrophysiological, pharmacological and mechanical studies with a preserved in vivo like tissue structure and direct access of the measurement technology to all regions of the heart. Physiological action potential properties have been demonstrated in embryonic, neonatal and adult slices 9,10,11. Vitality of the slices, except for the surface layers directly damaged by the slicing procedure, h...

Thin tissue slices have been used frequently in basic science since Yamamot and Mcllwain showed in 1966 that electrical activity of brain slices is maintained in vitro1. Since then, electrophysiological and pharmacological studies have been conducted on slices from brain 2, liver 3, lung 4 and myocardial tissue 5,6,7. First patch-clamp recordings in ventricular slices from neonatal rat hearts were described in 1990 8, but this technique fell into oblivion for some time. More than one decade later, our group established a new method to prepare murine embryonic 9, neonatal 10 and adult 11 heart slices. These viable tissue slices can be used for acute experiments (adult slices can be cultivated for several hours) or short-term culture experiments (embryonic and neonatal slices can be cultivated for a few days). Slices show in vivo like electrophysiological characteristics and a homogenous excitation spread as assessed by sharp electrode action potential and micro electrode array recordings 11. Due to their &#34;two-dimensional&#34; morphology, they allow direct access of recording electrodes to all regions of the ventricle, which makes them an interesting tool for electrophysiological investigations and raises new experimental options in comparison to Langendorff-perfused whole hearts. Drug response of the slices to ion channel blockers like verapamil (L-type Ca2+-channel blocker), lidocain (Na+-channel blocker), 4-aminopyridine (unselective voltage dependent K+-channel blocker) and linopirdine (KCNQ K+-channel blocker) 9,11 corresponded to known effects on dissociated cardiomyocytes. Isometric force measurements revealed a positive force frequency relationship and strongly suggested intact contractile function 10. These findings demonstrated that murine ventricular slices are suitable as an in vitro tissue model for physiological and pharmacological studies. Furthermore, ventricular slices of recipient hearts in combination with sharp electrode recordings have proven to be a very helpful tool to characterize electrical and mechanical integration as well as maturation of transplanted fetal 12,13,14 and stem cell-derived 15 cardiomyocytes.
In summary, ventricular slices are a valuable and well-establish multicellular tissue model and should be considered complementary to dissociated cardiomyocytes and Langendorff-perfused hearts in cardiovascular research, with the major advantage of providing an in vivo like tissue structure (in contrast to dissociated cells) as well as direct access of measurement technologies like sharp electrode recordings to all regions of the heart (in contrast to whole heart preparations).

<table><tbody><tr><td>Leica VT 1000s</td><td>Leica Microsystems, Wetzlar, Germany</td><td></td><td>Microtome with vibrating blade.</td></tr><tr><td>Stainless Steel Blades</td><td>Campden Instruments, Loughborough, England</td><td>7550-1-SS</td><td></td></tr><tr><td>Pasteur pipettes</td><td>Sigma-Aldrich, St. Louise, USA</td><td>Z627992</td><td></td></tr><tr><td>Fine brush, &lt;em&gt;e.g.&lt;/em&gt; size 6 (4/32&quot;)</td><td>VWR, International, Radnor, USA</td><td>149-2125</td><td></td></tr><tr><td>Preparation table</td><td></td><td></td><td>self made</td></tr><tr><td>Molt for embedding ventricles in agarose</td><td></td><td></td><td>self made</td></tr><tr><td>1 mL Syringe</td><td>Becton, Dickinson; Franklin Lakes, USA</td><td>300013</td><td></td></tr><tr><td>27 G x 3/4`` Needles</td><td>Braun, Melsungen, Germany</td><td>4657705</td><td></td></tr><tr><td>20 G 11/2`` Needles</td><td>4657519</td><td></td><td></td></tr><tr><td>Small scissor</td><td>WPI, Sarasota, USA</td><td>501263</td><td></td></tr><tr><td>Tweezers #5, 0.1 x 0.06 mm tip</td><td>WPI, Sarasota, USA</td><td>500342</td><td></td></tr><tr><td>Oxygen gas (medical grade O&lt;sub&gt;2&lt;/sub&gt;)</td><td>Linde, Munich, Germany</td><td></td><td></td></tr><tr><td>Carbogen gas (95 % O&lt;sub&gt;2&lt;/sub&gt;, 5 % CO&lt;sub&gt;2&lt;/sub&gt;)</td><td>Linde, Munich, Germany</td><td></td><td></td></tr><tr><td>NaCl</td><td>Sigma-Aldrich, St. Louise, USA</td><td>7647-14-5</td><td></td></tr><tr><td>KCl</td><td>Sigma-Aldrich, St. Louise, USA</td><td>746436</td><td></td></tr><tr><td>CaCl&lt;sub&gt;2&lt;/sub&gt;</td><td>Sigma-Aldrich, St. Louise, USA</td><td>746495</td><td></td></tr><tr><td>KH&lt;sub&gt;2&lt;/sub&gt;PO&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich, St. Louise, USA</td><td>NIST200B</td><td></td></tr><tr><td>HEPES</td><td>Sigma-Aldrich, St. Louise, USA</td><td>51558</td><td></td></tr><tr><td>NaHCO&lt;sub&gt;3&lt;/sub&gt;</td><td>Sigma-Aldrich, St. Louise, USA</td><td>S5761</td><td></td></tr><tr><td>D(+)-Glucose</td><td>Sigma-Aldrich, St. Louise, USA</td><td>G8270</td><td></td></tr><tr><td>MgSO&lt;sub&gt;4&lt;/sub&gt;</td><td>Sigma-Aldrich, St. Louise, USA</td><td>M7506</td><td></td></tr><tr><td>NaOH</td><td>Sigma-Aldrich, St. Louise, USA</td><td>S8045</td><td></td></tr><tr><td>Cyanoacrylate glue</td><td>Henkel, D&amp;uuml;sseldorf, Germany</td><td></td><td></td></tr><tr><td>Low-melt Agarose</td><td>Roth, Karlsruhe, Germany</td><td>6351.2</td><td></td></tr><tr><td>Heparin-sodium-25000 I.E./5 mL</td><td>Ratiopharm, Ulm, Germany</td><td></td><td></td></tr><tr><td>Dulbecco&#039;s Modified Eagle Medium (DMEM), high glucose, GlutaMAX</td><td>ThermoScientific, Waltham, USA</td><td>10566016</td><td></td></tr><tr><td>SEC-10LX Amplifier</td><td>npi electronic GmbH, Tamm, Germany</td><td>SEC-10LX</td><td></td></tr><tr><td>EPC 9</td><td>HEKA Elektronik GmbH, Lambrecht, Germany</td><td></td><td></td></tr><tr><td>Zeiss Axiovert 200</td><td>Zeiss, Oberkochen, Germany</td><td></td><td></td></tr><tr><td>Low magnification Micromanipulator</td><td>Narashige, Tokyo, Japan</td><td>Nm-3</td><td></td></tr><tr><td>High magnification, three-axis micromanipulator</td><td>Narashige, Tokyo, Japan</td><td>MHW-3</td><td></td></tr><tr><td>Peristaltic perfusion pump</td><td>Multi Channel Systems, Reutlingen, Germany</td><td>PPS2</td><td></td></tr><tr><td>2-channel temperature controller</td><td>Multi Channel Systems, Reutlingen, Germany</td><td>TCO02</td><td></td></tr><tr><td>Square pulse stimulator</td><td>Natus Europe GmbH, Planegg, Germany</td><td>Grass SD9</td><td></td></tr><tr><td>Glass capillaries</td><td>WPI, Sarasota, USA</td><td>1B150F-1</td><td></td></tr></tbody></table>

murine short axis ventricular heart slices for electrophysiological studies

Murine cardiomyocytes have been extensively used for in vitro studies of cardiac physiology and new therapeutic strategies. However, multicellular preparations of dissociated cardiomyocytes are not representative of the complex in vivo structure of cardiomyocytes, non-myocytes and extracellular matrix, which influences both mechanical and electrophysiological properties of the heart. Here we describe a technique to prepare viable ventricular slices of adult mouse hearts with a preserved in vivo like tissue structure, and demonstrate their suitability for electrophysiological recordings. After excision of the heart, ventricles are separated from the atria, perfused with Ca2+-free solution containing 2,3-butanedione monoxime and embedded in a 4% low-melt agarose block. The block is placed on a microtome with a vibrating blade, and tissue slices with a thickness of 150-400 &#181;m are prepared keeping the vibration frequency of the blade at 60-70 Hz and moving the blade forward as slowly as possible. Thickness of the slices depends on the further application. Slices are stored in ice cold Tyrode&#39;s solution with 0.9 mM Ca2+ and 2,3-butanedione monoxime (BDM) for 30 min. Afterwards, slices are transferred to 37 &#176;C DMEM for 30 min to wash out the BDM. Slices can be used for electrophysiological studies with sharp electrodes or micro electrode arrays, for force measurements to analyze contractile function or to investigate the interaction of transplanted stem cell-derived cardiomyocytes and host tissue. For sharp electrode recordings, a slice is placed into a 3 cm cell culture dish on the heating plate of an inverted microscope. The slice is stimulated with a unipolar electrode, and intracellular action potentials of cardiomyocytes within the slice are recorded with a sharp glass electrode.

Myocardial infarction leads to a virtually irreversible loss of cardiomyocytes. Cell replacement therapy using stem cell-derived cardiomyocytes for exogenous cardiac regeneration is a promising therapeutic approach. Electrical integration and maturation of the transplanted cells are crucial for safety and efficiency of cell replacement therapy.
To assess integration and maturation, we transplanted cardiomyocytes derived from ind...

Watch this Scientific Journal Video about Murine Short Axis Ventricular Heart Slices for Electrophysiological Studies at JoVE.com

Murine Short Axis Ventricular Heart Slices for Electrophysiological Studies

Here, we describe the preparation of viable ventricular slices from adult mice and their use for sharp electrode action potential recordings. These multicellular preparations provide a preserved in vivo like tissue structure, which makes them a valuable model for electrophysiological and pharmacological studies in vitro.

Murine cardiomyocytes have been extensively used for in vitro studies of cardiac physiology and new therapeutic strategies. However, multicellular ...

murine-short-axis-ventricular-heart-slices-for-electrophysiological

Research

JoVE Journal

Medicine

7.3K Views.  University of Cologne. Here, we describe the preparation of viable ventricular slices from adult mice and their use for sharp electrode action potential recordings. These multicellular preparations provide a preserved in vivo like tissue structure, which makes them a valuable model for electrophysiological and pharmacological studies in vitro.

Video: Murine Short Axis Ventricular Heart Slices for Electrophysiological Studies

Optical Mapping of Action Potentials and Calcium Transients in the Mouse Heart

The mouse heart is a popular model for cardiovascular studies due to the existence of low cost technology for genetic engineering in this species. Cardiovascular physiological phenotyping of the mouse heart can be easily done using fluorescence imaging employing various probes for transmembrane potential (Vm), calcium transients (CaT), and other parameters. Excitation-contraction coupling is characterized by action potential and intracellular calcium dynamics; therefore, it is critically important to map both Vm and CaT simultaneously from the same location on the heart1-4. Simultaneous optical mapping from Langendorff perfused mouse hearts has the potential to elucidate mechanisms underlying heart failure, arrhythmias, metabolic disease, and other heart diseases. Visualization of activation, conduction velocity, action potential duration, and other parameters at a myriad of sites cannot be achieved from cellular level investigation but is well solved by optical mapping1,5,6. In this paper we present the instrumentation setup and experimental conditions for simultaneous optical mapping of Vm and CaT in mouse hearts with high spatio-temporal resolution using state-of-the-art CMOS imaging technology. Consistent optical recordings obtained with this method illustrate that simultaneous optical mapping of Langendorff perfused mouse hearts is both feasible and reliable.

This paper details the dissection procedure, instrumental setup, and experimental conditions during optical mapping of transmembrane potential (Vm) and intracellular calcium transient (CaT) in intact isolated Langendorff perfused mouse hearts.

The mouse heart is a popular model for cardiovascular studies due to the existence of low cost technology for genetic engineering in this species. ...

Bioengineering

Optical Imaging of Isolated Murine Ventricular Myocytes

The ability to isolate adult cardiac myocytes has permitted researchers to study a variety of cardiac pathologies at the single cell level. While advances in calcium sensitive dyes have permitted the robust optical recording of single cell calcium dynamics, recording of robust transmembrane optical voltage signals has remained difficult. Arguably, this is because of the low single to noise ratio, phototoxicity, and photobleaching of traditional potentiometric dyes. Therefore, single cell voltage measurements have long been confined to the patch clamp technique which while the gold standard, is technically demanding and low throughput. However, with the development of novel potentiometric dyes, large, fast optical responses to changes in voltage can be obtained with little to no phototoxicity and photobleaching. This protocol describes in detail how to isolate adult murine myocytes which can be used for cellular shortening, calcium, and optical voltage measurements. Specifically, the protocol describes how to use a ratiometric calcium dye, a single-excitation calcium dye, and a single excitation voltage dye. This approach can be used to assess the cardiotoxicity and arrhythmogenicity of various chemical agents. While phototoxicity is still an issue at the single cell level, methodology is discussed on how to reduce it.

We present the methodology for the isolation of murine myocytes and how to obtain voltage or calcium traces simultaneously with sarcomere shortening traces using fluorescence photometry with simultaneous digital cell geometry measurements.

The ability to isolate adult cardiac myocytes has permitted researchers to study a variety of cardiac pathologies at the single cell level. While advances ...

Preclinical Cardiac Electrophysiology Assessment by Dual Voltage and Calcium Optical Mapping of Human Organotypic Cardiac Slices

Human cardiac slice preparations have recently been developed as a platform for human physiology studies and therapy testing to bridge the gap between animal and clinical trials. Numerous animal and cell models have been used to examine the effects of drugs, yet these responses often differ in humans. Human cardiac slices offer an advantage for drug testing in that they are directly derived from viable human hearts. In addition to having preserved multicellular structures, cell-cell coupling, and extracellular matrix environments, human cardiac tissue slices can be used to directly test the effect of innumerable drugs on adult human cardiac physiology. What distinguishes this model from other heart preparations, such as whole hearts or wedges, is that slices can be subjected to longer-term culture. As such, cardiac slices allow for studying the acute as well as chronic effects of drugs. Furthermore, the ability to collect several hundred to a thousand slices from a single heart makes this a high-throughput model to test several drugs at varying concentrations and combinations with other drugs at the same time. Slices can be prepared from any given region of the heart. In this protocol, we describe the preparation of left ventricular slices by isolating tissue cubes from the left ventricular free wall and sectioning them into slices using a high precision vibrating microtome. These slices can then either be subjected to acute experiments to measure baseline cardiac electrophysiological function or cultured for chronic drug studies. This protocol also describes dual optical mapping of cardiac slices for simultaneous recordings of transmembrane potentials and intracellular calcium dynamics to determine the effects of the drugs being investigated.

This protocol describes the procedure for sectioning and culturing human cardiac slices for preclinical drug testing and details the use of optical mapping for recording transmembrane voltage and intracellular calcium signals simultaneously from these slices.

Human cardiac slice preparations have recently been developed as a platform for human physiology studies and therapy testing to bridge the gap between ...

Electrophysiological Assessment of Murine Atria with High-Resolution Optical Mapping

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and electrophysiological phenotype in the atria. That encourages us to utilize a genetically-engineered mouse model to elucidate the mechanism of AF. However, it is difficult to evaluate the electrophysiological properties in murine atria due to their small size. This protocol describes the electrophysiological evaluation of atria using an optical mapping system with a high temporal and spatial resolution in Langendorff perfused murine hearts. The optical mapping system is assembled with dual high-speed complementary metal oxide semiconductor cameras and high magnification objective lenses, to detect the fluorescence of a voltage-sensitive dye and Ca2+ indicator. To focus on the assessment of murine atria, optical mapping is performed with an area of 2 mm &#215; 2 mm or 10 mm x 10 mm, with a 100 &#215; 100 resolution (20 &#181;m/pixel or 100 &#181;m/pixel) and sampling rate of up to 10 kHz (0.1 ms) at maximum. A 1-French size quadripolar electrode pacing catheter is placed into the right atrium through the superior vena cava avoiding any mechanical damage to the atrium, and pacing stimulation is delivered through the catheter. An electrophysiological study is performed with programmed stimulation including constant pacing, burst pacing, and up to triple extrastimuli pacing. Under a spontaneous or pacing rhythm, the optical mapping recorded the action potential duration, activation map, conduction velocity, and Ca2+ transient individually in the right and left atria. In addition, the programmed stimulation also determines the inducibility of atrial tachyarrhythmias. Precise activation mapping is performed to identify the propagation of the excitation in the atrium during an induced atrial tachyarrhythmia. Optical mapping with a specialized setting enables a thorough electrophysiological evaluation of the atrium in murine pathological models.

This protocol describes the electrophysiological evaluation of murine atria utilizing an optical mapping system with a high temporal and spatial resolution, including dual recordings of the membrane voltage and Ca2+ transient under programmed stimulation through a specialized electrode catheter.

Recent genome-wide association studies targeting atrial fibrillation (AF) have indicated a strong association between the genotype and ...

Isolation and Kv Channel Recordings in Murine Atrial and Ventricular Cardiomyocytes

KCNE genes encode for a small family of Kv channel ancillary subunits that form heteromeric complexes with Kv channel alpha subunits to modify their functional properties. Mutations in KCNE genes have been found in patients with cardiac arrhythmias such as the long QT syndrome and/or atrial fibrillation. However, the precise molecular pathophysiology that leads to these diseases remains elusive. In previous studies the electrophysiological properties of the disease causing mutations in these genes have mostly been studied in heterologous expression systems and we cannot be sure if the reported effects can directly be translated into native cardiomyocytes. In our laboratory we therefore use a different approach. We directly study the effects of KCNE gene deletion in isolated cardiomyocytes from knockout mice by cellular electrophysiology - a unique technique that we describe in this issue of the Journal of Visualized Experiments. The hearts from genetically engineered KCNE mice are rapidly excised and mounted onto a Langendorff apparatus by aortic cannulation. Free Ca2+ in the myocardium is bound by EGTA, and dissociation of cardiac myocytes is then achieved by retrograde perfusion of the coronary arteries with a specialized low Ca2+ buffer containing collagenase. Atria, free right ventricular wall and the left ventricle can then be separated by microsurgical techniques. Calcium is then slowly added back to isolated cardiomyocytes in a multiple step comprising washing procedure. Atrial and ventricular cardiomyocytes of healthy appearance with no spontaneous contractions are then immediately subjected to electrophysiological analyses by patch clamp technique or other biochemical analyses within the first 6 hours following isolation.

Kv channel dysfunction is associated with cardiac arrhythmias. In order to study the molecular mechanisms that lead to such arrhythmias we utilize a systematic protocol for isolation of atrial and ventricular cardiomyocytes from Kv channel ancillary subunit knockout mice. Isolated cardiomyocytes can then immediately be used for cellular electrophysiological studies, biochemical or immunofluorescence (IF) assays.

KCNE genes encode for a small family of Kv channel ancillary subunits that form heteromeric complexes with Kv channel alpha subunits to modify their ...

Biology

Optocardiography and Electrophysiology Studies of Ex Vivo Langendorff-perfused Hearts

Small animal models are most commonly used in cardiovascular research due to the availability of genetically modified species and lower cost compared to larger animals. Yet, larger mammals are better suited for translational research questions related to normal cardiac physiology, pathophysiology, and preclinical testing of therapeutic agents. To overcome the technical barriers associated with employing a larger animal model in cardiac research, we describe an approach to measure physiological parameters in an isolated, Langendorff-perfused piglet heart. This approach combines two powerful experimental tools to evaluate the state of the heart: electrophysiology (EP) study and simultaneous optical mapping of transmembrane voltage and intracellular calcium using parameter sensitive dyes (RH237, Rhod2-AM). The described methodologies are well suited for translational studies investigating the cardiac conduction system, alterations in action potential morphology, calcium handling, excitation-contraction coupling and the incidence of cardiac alternans or arrhythmias.

The objective of this study was to establish a method for investigating cardiac dynamics using a translational animal model. The described experimental approach incorporates dual-emission optocardiography in conjunction with an electrophysiological study to assess electrical activity in an isolated, intact porcine heart model.

Small animal models are most commonly used in cardiovascular research due to the availability of genetically modified species and lower cost compared to ...

Microelectrode Array Recording of Sinoatrial Node Firing Rate to Identify Intrinsic Cardiac Pacemaking Defects in Mice

The sinoatrial node (SAN), located in the right atrium, contains the pacemaker cells of the heart, and dysfunction of this region can cause tachycardia or bradycardia. Reliable identification of cardiac pacemaking defects requires the measurement of intrinsic heart rates by largely preventing the influence of the autonomic nervous system, which can mask rate deficits. Traditional methods to analyze intrinsic cardiac pacemaker function include drug-induced autonomic blockade to measure in vivo heart rates, isolated heart recordings to measure intrinsic heart rates, and sinoatrial strip or single-cell patch-clamp recordings of sinoatrial pacemaker cells to measure spontaneous action potential firing rates. However, these more traditional techniques can be technically challenging and difficult to perform. Here, we present a new methodology to measure intrinsic cardiac firing rate by performing microelectrode array (MEA) recordings of whole-mount sinoatrial node preparations from mice. MEAs are composed of multiple microelectrodes arranged in a grid-like pattern for recording in vitro extracellular field potentials. The method described herein has the combined advantage of being relatively faster, simpler, and more precise than previous approaches for recording intrinsic heart rates, while also allowing easy pharmacological interrogation.

This protocol aims to describe a new methodology to measure intrinsic cardiac firing rate using microelectrode array recording of the whole sinoatrial node tissue to identify pacemaking defects in mice. Pharmacological agents can also be introduced in this method to study their effects on intrinsic pacemaking.

The sinoatrial node (SAN), located in the right atrium, contains the pacemaker cells of the heart, and dysfunction of this region can cause tachycardia or ...

Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices

The isolation of ventricular cardiac myocytes from animal and human hearts is a fundamental method in cardiac research. Animal cardiomyocytes are commonly isolated by coronary perfusion with digestive enzymes. However, isolating human cardiomyocytes is challenging because human myocardial specimens usually do not allow for coronary perfusion, and alternative isolation protocols result in poor yields of viable cells. In addition, human myocardial specimens are rare and only regularly available at institutions with on-site cardiac surgery. This hampers the translation of findings from animal to human cardiomyocytes. Described here is a reliable protocol that enables efficient isolation of ventricular myocytes from human and animal myocardium. To increase the surface-to-volume ratio while minimizing cell damage, myocardial tissue slices 300 &#181;m thick are generated from myocardial specimens with a vibratome. Tissue slices are then digested with protease and collagenase. Rat myocardium was used to establish the protocol and quantify yields of viable, calcium-tolerant myocytes by flow-cytometric cell counting. Comparison with the commonly used tissue-chunk method showed significantly higher yields of rod-shaped cardiomyocytes (41.5 &#177; 11.9 vs. 7.89 &#177; 3.6%, p &#60; 0.05). The protocol was translated to failing and non-failing human myocardium, where yields were similar as in rat myocardium and, again, markedly higher than with the tissue-chunk method (45.0 &#177; 15.0 vs. 6.87 &#177; 5.23 cells/mg, p &#60; 0.05). Notably, with the protocol presented it is possible to isolate reasonable numbers of viable human cardiomyocytes (9&#8211;200 cells/mg) from minimal amounts of tissue (&#60;50 mg). Thus, the method is applicable to healthy and failing myocardium from both human and animal hearts. Furthermore, it is possible to isolate excitable and contractile myocytes from human tissue specimens stored for up to 36 h in cold cardioplegic solution, rendering the method particularly useful for laboratories at institutions without on-site cardiac surgery.

Presented is a protocol for the isolation of human and animal ventricular cardiomyocytes from vibratome-cut myocardial slices. High yields of calcium-tolerant cells (up to 200 cells/mg) can be obtained from small amounts of tissue (&#60;50 mg). The protocol is applicable to myocardium exposed to cold ischemia for up to 36 h.

The isolation of ventricular cardiac myocytes from animal and human hearts is a fundamental method in cardiac research. Animal cardiomyocytes are commonly ...

Isolation of High Quality Murine Atrial and Ventricular Myocytes for Simultaneous Measurements of Ca2+ Transients and L-Type Calcium Current

Mouse models play a crucial role in arrhythmia research and allow studying key mechanisms of arrhythmogenesis including altered ion channel function and calcium handling. For this purpose, atrial or ventricular cardiomyocytes of high quality are necessary to perform patch-clamp measurements or to explore calcium handling abnormalities. However, the limited yield of high-quality cardiomyocytes obtained by current isolation protocols does not allow both measurements in the same mouse. This article describes a method to isolate high-quality murine atrial and ventricular myocytes via retrograde enzyme-based Langendorff perfusion, for subsequent simultaneous measurements of calcium transients and L-type calcium current from one animal. Mouse hearts are obtained, and the aorta is rapidly cannulated to remove blood. Hearts are then initially perfused with a calcium-free solution (37 &#176;C) to dissociate the tissue at the level of intercalated discs and afterwards with an enzyme solution containing little calcium to disrupt extracellular matrix (37 &#176;C). The digested heart is subsequently dissected into atria and ventricles. Tissue samples are chopped into small pieces and dissolved by carefully pipetting up and down. The enzymatic digestion is stopped, and cells are stepwise reintroduced to physiologic calcium concentrations. After loading with a fluorescent Ca2+-indicator, isolated cardiomyocytes are prepared for simultaneous measurement of calcium currents and transients. Additionally, isolation pitfalls are discussed and patch-clamp protocols and representative traces of L-type calcium currents with simultaneous calcium transient measurements in atrial and ventricular murine myocytes isolated as described above are provided.

Isolation of High Quality Murine Atrial and Ventricular Myocytes for Simultaneous Measurements of Ca2+ Transients and L-Type Calcium Current

Mouse models allow studying key mechanisms of arrhythmogenesis. For this purpose, high quality cardiomyocytes are necessary to perform patch-clamp measurements. Here, a method to isolate murine atrial and ventricular myocytes via retrograde enzyme-based Langendorff perfusion, which allows simultaneous measurements of calcium-transients and L-type calcium current, is described.

Mouse models play a crucial role in arrhythmia research and allow studying key mechanisms of arrhythmogenesis including altered ion channel function and ...

Generation of Porcine Ventricular Slices: A Vibratome-based Technique to Prepare Ultra-thin Slices of Pig Heart Tissue

Source: Ou, Q. et. al., <a href="https://www.jove.com/v/60913">Slicing and Culturing Pig Hearts under Physiological Conditions.</a> J. Vis. Exp. (2020)
This video demonstrates a vibratome-based procedure to generate viable, ultra-thin sections of pig heart. The prepared tissue slices can be cultured and used as model systems for pharmacological testing.

Wytwarzanie plastrów komór świń: technika oparta na wibratomie do przygotowywania ultracienkich plastrów tkanki serca świni

Source: Ou, Q. et. al., Slicing and Culturing Pig Hearts under Physiological Conditions. J. Vis. Exp. (2020)
This video demonstrates a vibratome-based ...