We would like to thank Andreas Dendorfer from the Walter-Brendel-Centre of Experimental Medicine, LMU Munich, for help with the slicing protocol. For providing human myocardial tissue samples we would like to thank Ghazali Minabari and Christian Heim from the Department of Cardiac Surgery, University Hospital Erlangen, Hendrik Milting from the Erich &#38; Hanna Klessmann Institute, Ruhr-University Bochum and Muhannad Alkassar from the Department of Pediatric Cardiology, University Hospital Erlangen. For support with flow cytometry we would like to thank Simon V&#246;lkl and colleagues from the translational research center (TRC), University Hospital Erlangen. We would also like to thank Lorenz McCargo and Celine Gr&#252;ninger from the Institute of Cellular and Molecular Physiology Erlangen for excellent technical support.
This work was supported by the DZHK (German Centre for Cardiovascular Research), by the Interdisciplinary Centre for Clinical Research (IZKF) at the University Hospital of the University of Erlangen-N&#252;rnberg, and the Universit&#228;tsbund Erlangen-N&#252;rnberg.

All experiments with rats were approved by the Animal Care and Use Committee Mittelfranken, Bavaria, Germany. Collection and use of human cardiac tissue samples was approved by the Institutional Review Boards of the University of Erlangen-N&#252;rnberg and the Ruhr-University Bochum. Studies were conducted according to Declaration of Helsinki guidelines. Patients gave their written informed consent prior to tissue collection.
Female Wistar rats (150&#8211;200 g) were commercially obtained, anesthetized by injecting 100 mg/kg of thiopental-sodium intraperitoneally, and euthanized by cervical dislocation followed by thoracotomy and excision of the heart. Human cardiac tissue samples were collected from the left-ventricular apical core during implantation of mechanical assist devices, from septal myectomy, from tetralogy of Fallot corrective surgery, or from the free left-ventricular wall of explanted hearts. The following protocol describes the isolation from human ventricular tissue. The isolation of rat cardiomyocytes was performed accordingly, but with different enzymes (see&#160;Table of Materials). A schematic workflow of the protocol is illustrated in&#160;Figure 1.
1. Preparation of buffers, solutions, and enzymes
<ol>
	<li>Prepare buffers and solutions as listed in Table 1.</li>
	<li>Warm up solutions 1, 2, 3 and the modified Tyrode&#8217;s solution to 37 &#176;C. Store the cutting solution at 4 &#176;C until use. 
	NOTE: For 1&#8211;2 myocardial slices a total of approximately 15 mL, 8 mL, and 5 mL of solutions 1, 2, and 3 are required for the isolation in one 35 mm tissue culture dish. Scale up accordingly for simultaneous myocyte isolations in multiple dishes. Cutting solution can be frozen and kept at -20 &#730;C for several months.</li>
	<li>Weigh 1 mg of proteinase XXIV (see Table of Materials) into a prechilled 15 mL centrifuge tube and store on ice until use. This is for processing one sample. Scale up the amount accordingly. Do not mix the proteinase and collagenase.</li>
	<li>Weigh 8 mg of collagenase CLSI (see Table of Materials) into a prechilled 15 mL centrifuge tube and store on ice until use. This is for processing one sample. Scale up the amount accordingly. Do not mix the proteinase and collagenase. 
	CAUTION: Wear a face mask or work under a fume hood to avoid inhalation of enzyme powder. 
	NOTE: Enzyme activity may vary in different lots. Therefore, the optimal concentration may differ and should be determined with each newly purchased enzyme16.</li>
</ol>
2. Storage and transport of myocardial tissue
<ol>
	<li>Store and transport human cardiac samples in cooled, 4 &#730;C cutting solution (Table 1).</li>
	<li>Use the same solution for further tissue processing and vibratome slicing. 
	NOTE: Biopsies and surgical heart samples should be transferred immediately to the cutting solution at 4 &#176;C and can then be stored or transported at 4 &#176;C for a maximum of 36 h before the application of this protocol.</li>
</ol>
3. Processing and slicing of the tissue
NOTE: The protocol for tissue slicing follows Fischer et al.15.
<ol>
	<li>Trimming of the tissue block 
	CAUTION: Human cardiac tissue is potentially infectious. Always use protective wear and follow safety regulations of your institution. Carefully handle used blades and discard in safety containers.
	<ol>
		<li>Place the specimen into a 100 mm tissue culture dish filled with 20 mL cold cutting solution and keep on a cooled, 4 &#176;C plate.</li>
		<li>Remove excess fibrotic tissue and epicardial fat with a scalpel. In case of a transmural specimen, remove trabeculae and tissue layers near the endocardium. 
		NOTE: Fibrotic tissue is stiff and appears white. Fat is typically soft and appears white to yellow. Trabeculae and endocardial tissue layers can be identified from their loose tissue composition and a nonaligned fiber orientation compared to myocardium of the epicardial layers</li>
		<li>For optimal vibratome processing, cut rectangular tissue blocks of approximately 8 mm x 8 mm x 8 mm with a scalpel from a larger tissue specimen. For smaller biopsies skip this step and move to agarose embedding.</li>
	</ol>
	</li>
	<li>Embedding cardiac tissue into low-melting-point agarose
	<ol>
		<li>Boil 400 mg of low-melting point agarose in 10 mL of cutting solution in a glass beaker. 
		CAUTION: Wear gloves and safety glasses to avoid burns. Handle hot glassware only with heat protection wear.</li>
		<li>Fill a 10 mL syringe with the hot, dissolved agarose gel. Seal the syringe and allow the agarose to equilibrate in a 37 &#176;C water bath for at least 15 min.</li>
		<li>Use forceps to place the trimmed cardiac specimen or biopsy into a clean 35 mm tissue culture dish with the epicardium facing down and remove excess fluid with a sterile swab.</li>
		<li>Pour the equilibrated agarose (step 3.2.2) over the tissue by emptying the syringe. Secure the tissue against movement with forceps while pouring the agarose. Make sure that the tissue is completely immersed in agarose.</li>
		<li>Immediately place the dish on ice and let the agarose solidify for 10 min.</li>
	</ol>
	</li>
	<li>Slicing the myocardium
	<ol>
		<li>Mount a new&#160;razor blade to the blade holder of the vibratome and calibrate the vibratome by adjusting the z-deflection of the blade if possible. 
		NOTE: This protocol uses a vibratome with an infrared-assisted calibration device to align the blade in a horizontal position with minimal z-deflection (measured deflection &#60;0.1 &#181;m).</li>
		<li>Use a scalpel to excise an agarose-tissue block that fits the specimen holder of the vibratome. To ensure stability, make sure the tissue is still sufficiently immersed in agarose (agarose margins &#8805; 8 mm).</li>
		<li>Fix the agarose block to the specimen holder with a thin layer of cyanoacrylate glue and gentle pressure.</li>
		<li>Place the specimen holder with the tissue into the vibratome bath. Fill the bath with cutting solution and keep at 4&#8211;6 &#176;C throughout the processing with crushed ice, filled in the outer cooling tank of the vibratome.</li>
		<li>Generate 300 &#181;m thick slices with an advancing speed of &#8804;0.1 mm/s, an oscillating frequency of 80 Hz, a lateral amplitude of 1.5 mm, and a blade angle of 15&#176;. When handling the slices, hold the agarose instead of the tissue itself to avoid tissue damage. Store the slices in the cutting solution at 4 &#176;C for a maximum of 2 h, if necessary. 
		NOTE: Cardiomyocytes are oriented in parallel to the epicardium. Therefore, it is important to cut in parallel to the epicardium to avoid excessive myocyte damage. It is recommended to discard the first 1&#8211;3 slices, as only uniform slices of constant thickness should be used for the isolation. For small tissue biopsies, however, only discard the first slice.</li>
		<li>Check cardiomyocyte alignment under a standard light microscope with a magnification of 40-100x.</li>
	</ol>
	</li>
</ol>
4. Tissue digestion
<ol>
	<li>Place the heat plate on the lab shaker and warm it to 37 &#176;C. Start the lab shaker at 65 rpm.</li>
	<li>Dissolve the proteinase (prepared in step 1.3) in 2 mL of solution 1 (step 1.1 and 1.2) and incubate at 37 &#176;C until use. Do not mix the proteinase and collagenase.</li>
	<li>Dissolve the collagenase (prepared in step 1.4) in 2 mL of solution 1 (step 1.1 and 1.2) and incubate at 37 &#176;C until use. Do not mix the proteinase and collagenase. 
	CAUTION: Wear protective eyewear and gloves, because dissolved enzymes can cause skin and eye injuries.</li>
	<li>Add calcium chloride (CaCl2) to the collagenase containing solution (prepared in step 4.3) to a final concentration of 5 &#181;M.</li>
	<li>Use forceps to transfer a tissue slice from the vibratome bath to a clean 60 mm tissue culture dish filled with 5 mL of prechilled cutting solution (step 1.1 and 1.2) and keep on ice.</li>
	<li>Carefully remove the agarose from the myocardial tissue with blade or forceps. 
	NOTE: Avoid excess tension and shear stress on the myocardial slices, because they can damage the cardiomyocytes.</li>
	<li>To perform the initial wash, place a clean 35 mm tissue culture dish on the heat plate and fill it with 2 mL of prewarmed (37 &#176;C) solution 1. Transfer 1&#8211;2 myocardial slices to the prepared dish with forceps. Aspirate the solution with a 1 mL pipette and perform the wash steps 2x to remove remnants of cutting solution. 
	NOTE: Do not aspirate the cardiac slices. The solutions and the slices should remain at a constant temperature of 35 &#176;C on the agitated heat plate. Adjust the heat plate temperature if necessary.</li>
	<li>Remove solution 1 from the dish and add 2 mL of the proteinase solution (step 4.2). Incubate for 12 min on the heat plate at 65 rpm.</li>
	<li>Wash 2x with 2 mL of prewarmed solution 1 (37 &#176;C).</li>
	<li>Remove solution 1 from the dish and add 2 mL of collagenase solution (steps 4.3 and 4.4). Incubate at least 30 min on the heat plate at 65 rpm.</li>
	<li>Check for free individual myocytes at 30, 35, 40 min, etc., by placing the dish under a light microscope. Work quickly to avoid significant cooling of the solution. 
	NOTE: The required digestion time may vary depending on the tissue constitution and the degree of fibrosis. As soon as the tissue gets visibly soft and dissociates readily when gently pulled, the optimal digestion time has been reached. If enough tissue is available, several slices can be digested in parallel with varying digestion times.</li>
	<li>When the tissue is digested and individual myocytes are visible (step 4.11), wash 2x with 2 mL of prewarmed solution 2 (37 &#176;C) and fill again with 2 mL.</li>
</ol>
5. Tissue dissociation
<ol>
	<li>Dissociate the digested tissue slices with forceps by carefully pulling the fibers apart.</li>
	<li>Carefully pipette several times with a single-use Pasteur pipette (opening diameter &#62;2 mm). 
	NOTE: The use of forceps and pipetting can induce mechanical stress and cause cardiomyocyte damage. However, it is a crucial step for separation of the cells. Use fine forceps to minimize cell damage and carefully dissociate the slices to smaller pieces.</li>
	<li>Check for the liberated rod-shaped cardiomyocytes under the light microscope.</li>
</ol>
6. Reintroduction of physiological calcium concentration
<ol>
	<li>Slowly increase the calcium concentration from 5 &#181;M to 1.5 mM while agitating at 35 &#176;C on the heat plate. Use 10 mM and 100 mM CaCl2 stock solutions. Recommended steps: 20, 40, 80, 100, 150, 200, 400, 800, 1,200, 1,500 &#181;M. Allow the cells to adapt to the increased calcium levels in 5 min incubation intervals between each step.</li>
	<li>Remove undigested tissue chunks carefully with forceps or filter the cell suspension through a nylon mesh with 180 &#181;m pore size at the end of the calcium increase.</li>
</ol>
7. Removal of mechanical uncoupling agent
<ol>
	<li>Stop agitation and slowly remove one third of the solution (~700 &#181;L) from the top with a 1,000 &#181;L pipette. Avoid aspiration of the cardiomyocytes. 
	NOTE: If undigested tissue was removed, the cardiomyocytes will accumulate in the center of the dish, which facilitates aspiration of cell-free solution. If not, transfer the cell solution to a 15 mL centrifuge tube and allow the cells to sediment for 10 min at 35 &#176;C, then aspirate 700 &#181;L of the supernatant and discard, resuspend the cells, transfer them back to a 35 mm tissue culture dish and proceed with step 7.2.</li>
	<li>Add 700 &#181;L of solution 3 to the cells, resume agitation on the heat plate and incubate for 10 min.</li>
	<li>Repeat steps 7.1 and 7.2.</li>
	<li>Transfer the solution to a 15 mL centrifuge tube and allow the cardiomyocytes to sediment for a minimum of 10 min and a maximum of 30 min at room temperature or spin at 50 x g for 1 min. Remove the supernatant completely and resuspend in modified Tyrode&#8217;s solution or the desired experimentation buffer. 
	NOTE: Cardiomyocytes can be stored in modified Tyrode&#8217;s solution (Table 1) for several hours at 37 &#176;C and 5% CO2 before use.</li>
	<li>Verify the cell quality with a standard light microscope at 40x and 200x magnification. 
	NOTE: Around 30&#8211;50% of the cardiomyocytes should be rod-shaped, smooth without membrane blebs, and display clear cross-striations. Only 5&#8211;10% of the viable cells should show spontaneous contractions.</li>
</ol>

The authors have nothing to disclose.

Although the isolation of living cardiomyocytes was established more than 40 years ago and is still a prerequisite for many experimental approaches in cardiac research, it remains a difficult technique with unpredictable outcomes. Cardiomyocyte isolation via perfusion of the coronary arteries with enzyme solution is commonly used for hearts of small animals and yields large numbers of viable cells. However, this requires a relatively complex system and expertise. Furthermore, most human tissue samples are not suited for ...

A seminal technique that has paved the way to important insights into cardiomyocyte physiology is the isolation of living ventricular cardiomyocytes from intact hearts1. Isolated cardiomyocytes can be used to study normal cellular structure and function, or the consequences of in vivo experiments; for example, to assess changes in cellular electrophysiology or excitation-contraction coupling in animal models of cardiac disease. Additionally, isolated cardiomyocytes can be used for cell culture, pharmacological interventions, gene transfer, tissue engineering, and many other applications. Therefore, efficient methods for cardiomyocyte isolation are of fundamental value to basic and translational cardiac research.
Cardiomyocytes from small mammals, such as rodents, and from larger mammals, such as pigs or dogs, are commonly isolated by coronary perfusion of the heart with solutions containing crude collagenases and/or proteases. This has been described as the &#8220;gold standard&#8221; method for cardiomyocyte isolation, resulting in yields of up to 70% of viable cells2. The approach has also been used with human hearts, resulting in acceptable cardiomyocyte yields3,4,5. However, because coronary perfusion is only feasible if the intact heart or a large myocardial wedge containing a coronary artery branch is available, most human cardiac specimens are not suited for this approach due to their small size and a lack of appropriate vasculature. Therefore, the isolation of human cardiomyocytes is challenging.
Human myocardial specimens mostly consist of tissue chunks of variable size (approximately 0.5 x 0.5 x 0.5 cm to 2 x 2 x 2 cm), obtained through endomyocardial biopsies6, septal myectomies7, VAD implantations8, or from explanted hearts9. The most common procedures for cardiomyocyte isolation start with mincing the tissue using scissors or a scalpel. Cell-to-cell contacts are then disrupted by immersion in calcium-free or low-calcium buffers. This is followed by multiple digestion steps with crude enzyme extracts or purified enzymes like proteases (e.g., trypsin), collagenase, hyaluronidase, or elastase, resulting in a disintegration of the extracellular matrix and liberation of cardiomyocytes. In a final, critical step, a physiological calcium concentration has to be carefully restored, or cellular damage can occur due to the calcium-paradox10,11,12. This isolation approach is convenient but usually inefficient. For instance, one study found that nearly 1 g of myocardial tissue was required to obtain a sufficient number of cardiomyocytes suitable for subsequent experiments13. A possible reason for low yields is the relatively harsh method of mincing the tissue. This may particularly damage cardiomyocytes located at the chunk edges&#160;although these myocytes are most likely to be released by enzymatic digestion.
Another aspect that may influence isolation efficiency and quality of cells obtained from human specimens is the duration of tissue ischemia. Most protocols mention short transportation times to the laboratory as a prerequisite for good&#160;results. This restricts the study of human ventricular cardiomyocytes to laboratories with nearby cardiac surgery facilities. Together, these restrictions hamper the verification of important findings from animal models in human cardiomyocytes. Improved isolation protocols that allow for high cardiomyocyte yields from small amounts of tissue, preferably without serious damage after extended transportation times, are therefore desirable.
Described here is an isolation protocol based on the enzymatic digestion of thin myocardial tissue slices generated with a vibratome14,15. We demonstrate that isolation from tissue slices is much more efficient than that from tissue chunks minced with scissors. The described method not only allows for high yields of viable human cardiomyocytes from small amounts of myocardial tissue but is also applicable to specimens stored or transported in cold cardioplegic solution for up to 36 h.

<table>
	<tbody>
		<tr>
			<td>Chemicals</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>2,3-butanedionemonoxime</td>
			<td>Carl Roth</td>
			<td>3494.1</td>
			<td>Purity&#62;99%</td>
		</tr>
		<tr>
			<td>Bovine serum albumin</td>
			<td>Carl Roth</td>
			<td>163.2</td>
			<td></td>
		</tr>
		<tr>
			<td>CaCl2</td>
			<td>Carl Roth</td>
			<td>5239.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Creatine monohydrate</td>
			<td>Alfa Aesar</td>
			<td>B250009</td>
			<td></td>
		</tr>
		<tr>
			<td>Glucose</td>
			<td>Merck</td>
			<td>50-99-7</td>
			<td></td>
		</tr>
		<tr>
			<td>HEPES</td>
			<td>Carl Roth</td>
			<td>9105.3</td>
			<td></td>
		</tr>
		<tr>
			<td>KCl</td>
			<td>Carl Roth</td>
			<td>P017.1</td>
			<td></td>
		</tr>
		<tr>
			<td>KH2PO4</td>
			<td>Carl Roth</td>
			<td>3904.2</td>
			<td></td>
		</tr>
		<tr>
			<td>L-glutamic acid</td>
			<td>Fluka Biochemica</td>
			<td>49450</td>
			<td></td>
		</tr>
		<tr>
			<td>Low melting-point agarose</td>
			<td>Carl Roth</td>
			<td>6351.5</td>
			<td></td>
		</tr>
		<tr>
			<td>MgCl2 x 6H2O</td>
			<td>Carl Roth</td>
			<td>A537.1</td>
			<td></td>
		</tr>
		<tr>
			<td>MgSO4</td>
			<td>Sigma Aldrich</td>
			<td>M-7506</td>
			<td></td>
		</tr>
		<tr>
			<td>NaCl</td>
			<td>Carl Roth</td>
			<td>9265.1</td>
			<td></td>
		</tr>
		<tr>
			<td>NaHCO3</td>
			<td>Carl Roth</td>
			<td>8551.2</td>
			<td></td>
		</tr>
		<tr>
			<td>Paraformaldehyde</td>
			<td>Sigma Aldrich</td>
			<td>P6148</td>
			<td></td>
		</tr>
		<tr>
			<td>Taurine</td>
			<td>Sigma Aldrich</td>
			<td>T8691</td>
			<td></td>
		</tr>
		<tr>
			<td>Dyes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Di-8-ANEPPS</td>
			<td>Thermo Fisher Scientific</td>
			<td>D3167</td>
			<td></td>
		</tr>
		<tr>
			<td>Fluo-4 AM</td>
			<td>Thermo Fisher Scientific</td>
			<td>F14201</td>
			<td></td>
		</tr>
		<tr>
			<td>FluoVolt</td>
			<td>Thermo Fisher Scientific</td>
			<td>F10488</td>
			<td></td>
		</tr>
		<tr>
			<td>Enzymes</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase CLS type I</td>
			<td>Worthington</td>
			<td>LS004196</td>
			<td>Used for human tissue at 4 mg/mL 
			(activity: 280 U/mg)</td>
		</tr>
		<tr>
			<td>Collagenase CLS type II</td>
			<td>Worthington</td>
			<td>LS004176</td>
			<td>Used for rat tissue at 1.5 mg/mL 
			(activity 330 U/mg)</td>
		</tr>
		<tr>
			<td>Protease XIV</td>
			<td>Sigma Aldrich</td>
			<td>P8038</td>
			<td>Used for rat tissue at 0.5 mg/mL 
			(activity &#8805; 3.5 U/mg)</td>
		</tr>
		<tr>
			<td>Proteinase XXIV</td>
			<td>Sigma Aldrich</td>
			<td>P5147</td>
			<td>Used for human tissue at 0.5 mg/mL 
			(activity: 7-14 U/mg)</td>
		</tr>
		<tr>
			<td>Material</td>
			<td></td>
			<td></td>
			<td></td>
		</tr>
		<tr>
			<td>Cell analyzer (LSR Fortessa)</td>
			<td>BD Bioscience</td>
			<td>649225</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge tube, 15 mL</td>
			<td>Corning</td>
			<td>430790</td>
			<td></td>
		</tr>
		<tr>
			<td>Centrifuge tube, 50 mL</td>
			<td>Corning</td>
			<td>430829</td>
			<td></td>
		</tr>
		<tr>
			<td>Compact shaker</td>
			<td>Edmund B&#252;hler</td>
			<td>KS-15 B control</td>
			<td>Agitation direction: horizontal</td>
		</tr>
		<tr>
			<td>Disposable plastic pasteur-pipettes</td>
			<td>Carl Roth</td>
			<td>EA65.1</td>
			<td>For cell trituration use only pipettes with an inner tip diameter &#8805;2 mm</td>
		</tr>
		<tr>
			<td>Forceps</td>
			<td>FST</td>
			<td>11271-30</td>
			<td></td>
		</tr>
		<tr>
			<td>Heatblock</td>
			<td>VWR</td>
			<td>BARN88880030</td>
			<td></td>
		</tr>
		<tr>
			<td>Nylon net filter, 180 &#181;m</td>
			<td>Merck</td>
			<td>NY8H04700</td>
			<td></td>
		</tr>
		<tr>
			<td>TC Dish 100, Standard</td>
			<td>Sarstedt</td>
			<td>83.3902</td>
			<td></td>
		</tr>
		<tr>
			<td>TC Dish 35, Standard</td>
			<td>Sarstedt</td>
			<td>83.3900</td>
			<td></td>
		</tr>
		<tr>
			<td>TC Dish 60, Standard</td>
			<td>Sarstedt</td>
			<td>83.3901</td>
			<td></td>
		</tr>
		<tr>
			<td>Vibratome (VT1200S)</td>
			<td>Leica</td>
			<td>1491200S001</td>
			<td>Includes VibroCheck for infrared-assisted correction of z-deflection</td>
		</tr>
	</tbody>
</table>

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.

To verify isolation efficiency, the protocol was used with rat myocardium and the resulting number of viable myocytes was compared with the numbers obtained by isolation via coronary perfusion and by isolation from small tissue chunks (chunk isolation, Figure 2). Chunk isolation and isolation from tissue slices were performed from the same hearts. For the isolation via coronary perfusion, however, the whole heart was used. Coronary perfusion yielded predominantly rod-shaped and cross-striate...

Watch this Scientific Journal Video about Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices at JoVE.com

Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices

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 ...

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10.1K Views.  Friedrich-Alexander University Erlangen-Nürnberg. 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 (

Video: Isolation of Human Ventricular Cardiomyocytes from Vibratome-Cut Myocardial Slices

Isolation of Stem Cells from Human Pancreatic Cancer Xenografts

Cancer stem cells (CSCs) have been identified in a growing number of malignancies and are functionally defined by their ability to undergo self-renewal and produce differentiated progeny1. These properties allow CSCs to recapitulate the original tumor when injected into immunocompromised mice. CSCs within an epithelial malignancy were first described in breast cancer and found to display specific cell surface antigen expression (CD44+CD24low/-)2. Since then, CSCs have been identified in an increasing number of other human malignancies using CD44 and CD24 as well as a number of other surface antigens. Physiologic properties, including aldehyde dehydrogenase (ALDH) activity, have also been used to isolate CSCs from malignant tissues3-5.
Recently, we and others identified CSCs from pancreatic adenocarcinoma based on
ALDH activity and the expression of the cell surface antigens CD44 and CD24, and CD1336-8. These highly tumorigenic populations may or may not be overlapping and display other functions. We found that ALDH+ and CD44+CD24+ pancreatic CSCs are similarly tumorigenic, but ALDH+ cells are relatively more invasive8. In this protocol we describe a method to isolate viable pancreatic CSCs from low-passage human
xenografts9. Xenografted tumors are harvested from mice and made into a single-cell suspension. Tissue debris and dead cells are separated from live cells and then stained using antibodies against CD44 and CD24 and using the ALDEFLUOR reagent,
a fluorescent substrate of ALDH10. CSCs are then isolated by fluorescence activated cell sorting. Isolated CSCs can then be used for analytical or functional assays requiring viable cells.

Cancer stem cells (CSCs) have been identified in a number of malignancies. In this protocol we describe a flow cytometric method utilizing aldehyde dehydrogenase activity and CD44 and CD24 expression to isolate CSCs from human pancreatic adenocarcinoma xenografts. These viable cells can then be used in functional and analytical studies.

Cancer stem cells (CSCs) have been identified in a growing number of malignancies and are functionally defined by their ability to undergo self-renewal ...

Efficient Derivation of Human Cardiac Precursors and Cardiomyocytes from Pluripotent Human Embryonic Stem Cells with Small Molecule Induction

To date, the lack of a suitable human cardiac cell source has been the major setback in regenerating the human myocardium, either by cell-based transplantation or by cardiac tissue engineering1-3. Cardiomyocytes become terminally-differentiated soon after birth and lose their ability to proliferate. There is no evidence that stem/progenitor cells derived from other sources, such as the bone marrow or the cord blood, are able to give rise to the contractile heart muscle cells following transplantation into the heart1-3. The need to regenerate or repair the damaged heart muscle has not been met by adult stem cell therapy, either endogenous or via cell delivery1-3. The genetically stable human embryonic stem cells (hESCs) have unlimited expansion ability and unrestricted plasticity, proffering a pluripotent reservoir for in vitro derivation of large supplies of human somatic cells that are restricted to the lineage in need of repair and regeneration4,5. Due to the prevalence of cardiovascular disease worldwide and acute shortage of donor organs, there is intense interest in developing hESC-based therapies as an alternative approach. However, how to channel the wide differentiation potential of pluripotent hESCs efficiently and predictably to a desired phenotype has been a major challenge for both developmental study and clinical translation. Conventional approaches rely on multi-lineage inclination of pluripotent cells through spontaneous germ layer differentiation, resulting in inefficient and uncontrollable lineage-commitment that is often followed by phenotypic heterogeneity and instability, hence, a high risk of tumorigenicity6-8 (see a schematic in Fig. 1A). In addition, undefined foreign/animal biological supplements and/or feeders that have typically been used for the isolation, expansion, and differentiation of hESCs may make direct use of such cell-specialized grafts in patients problematic9-11. To overcome these obstacles, we have resolved the elements of a defined culture system necessary and sufficient for sustaining the epiblast pluripotence of hESCs, serving as a platform for de novo derivation of clinically-suitable hESCs and effectively directing such hESCs uniformly towards clinically-relevant lineages by small molecules12 (see a schematic in Fig. 1B). After screening a variety of small molecules and growth factors, we found that such defined conditions rendered nicotinamide (NAM) sufficient to induce the specification of cardiomesoderm direct from pluripotent hESCs that further progressed to cardioblasts that generated human beating cardiomyocytes with high efficiency (Fig. 2). We defined conditions for induction of cardioblasts direct from pluripotent hESCs without an intervening multi-lineage embryoid body stage, enabling well-controlled efficient derivation of a large supply of human cardiac cells across the spectrum of developmental stages for cell-based therapeutics.

We have established a protocol for induction of cardioblasts direct from pluripotent human embryonic stem cells maintained under defined conditions with small molecules, which enables derivation of a large supply of human cardiac progenitors and functional cardiomyocytes for cardiovascular repair.

To date, the lack of a suitable human cardiac cell source has been the major setback in regenerating the human myocardium, either by cell-based ...

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 ...

Isolation and Culture of Neonatal Mouse Cardiomyocytes

Cultured neonatal cardiomyocytes have long been used to study myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow for easy investigation and manipulation of biochemical pathways, and their effect on the biomechanical properties of spontaneously beating cardiomyocytes.	
The following 2-day protocol describes the isolation and culture of neonatal mouse cardiomyocytes. We show how to easily dissect hearts from neonates, dissociate the cardiac tissue and enrich cardiomyocytes from the cardiac cell-population. We discuss the usage of different enzyme mixes for cell-dissociation, and their effects on cell-viability. The isolated cardiomyocytes can be subsequently used for a variety of morphological, electrophysiological, biochemical, cell-biological or biomechanical assays. We optimized the protocol for robustness and reproducibility, by using only commercially available solutions and enzyme mixes that show little lot-to-lot variability. We also address common problems associated with the isolation and culture of cardiomyocytes, and offer a variety of options for the optimization of isolation and culture conditions.

Primary mouse cardiomyocyte cultures are one of the pivotal tools for the investigation of myofibrillar organization and function. The following protocol describes the isolation and culture of primary cardiomyocytes from neonatal mouse hearts. The resulting cardiomyocyte cultures may be subsequently used for a variety of biomechanical, biochemical and cell-biological assays.

Cultured neonatal cardiomyocytes have long been used to study  myofibrillogenesis and myofibrillar functions. Cultured cardiomyocytes allow  for easy ...

Generation of Human Cardiomyocytes: A Differentiation Protocol from Feeder-free Human Induced Pluripotent Stem Cells

In order to investigate the events driving heart development and to determine the molecular mechanisms leading to myocardial diseases in humans, it is essential first to generate functional human cardiomyocytes (CMs). The use of these cells in drug discovery and toxicology studies would also be highly beneficial, allowing new pharmacological molecules for the treatment of cardiac disorders to be validated pre-clinically on cells of human origin. Of the possible sources of CMs, induced pluripotent stem (iPS) cells are among the most promising, as they can be derived directly from readily accessible patient tissue and possess an intrinsic capacity to give rise to all cell types of the body 1. Several methods have been proposed for differentiating iPS cells into CMs, ranging from the classical embryoid bodies (EBs) aggregation approach to chemically defined protocols 2,3. In this article we propose an EBs-based protocol and show how this method can be employed to efficiently generate functional CM-like cells from feeder-free iPS cells.

Pluripotent stem cells, either embryonic or induced pluripotent stem (iPS) cells, constitute a valuable source of human differentiated cells, including cardiomyocytes. Here, we will focus on cardiac induction of iPS cells, showing how to use them to obtain functional human cardiomyocytes through an embryoid bodies-based protocol.

In order to investigate the events driving heart development and to determine the molecular mechanisms leading to myocardial diseases in humans, it is ...

Isolation of Embryonic Ventricular Endothelial Cells

Cell culture has greatly enhanced our ability to assess individual populations of cells under myriad culture conditions. While immortalized cell lines offer significant advantages for their ease of use, these cell lines are unavailable for all potential cell types. By isolating primary cells from a specific region of interest, particularly from a transgenic mouse, more nuanced studies can be performed. The basic technique involves dissecting the organ or partial organ of interest (e.g. the heart or a specific region of the heart) and dissociating the organ to single cells. These cells are then incubated with magnetic beads conjugated to an antibody that recognizes the cell type of interest. The cells of interest can then be isolated with the use of a magnet, with a short trypsin incubation dissociating the cells from the beads. These isolated cells can then be cultured and analyzed as desired. This technique was originally designed for adult mouse organs but can be easily scaled down for use with embryonic organs, as demonstrated herein. Because our interest is in the developing coronary vasculature, we wanted to study this population of cells during specific embryonic stages. Thus, the original protocol had to be modified to be compatible with the small size of the embryonic ventricles and the low potential yield of endothelial cells at these developmental stages. Utilizing this scaled-down approach, we have assessed coronary plexus remodeling in transgenic embryonic ventricular endothelial cells.

Primary cell culture is a useful technique for analyzing specific populations of cells, particularly from transgenic mouse embryos at specific developmental stages. Herein, embryonic ventricles are dissected and dissociated, and antibody-conjugated beads recognize and separate out the endothelial cells for further analysis.

Cell culture has greatly enhanced our ability to assess individual populations of cells under myriad culture conditions. While immortalized cell lines ...

Isolation and Physiological Analysis of Mouse Cardiomyocytes

Cardiomyocytes, the workhorse cell of the heart, contain exquisitely organized cytoskeletal and contractile elements that generate the contractile force used to pump blood. Individual cardiomyocytes were first isolated over 40 years ago in order to better study the physiology and structure of heart muscle. Techniques have rapidly improved to include enzymatic digestion via coronary perfusion. More recently, analyzing the contractility and calcium flux of isolated myocytes has provided a vital tool in the cellular and sub-cellular analysis of heart failure. Echocardiography and EKGs provide information about the heart at an organ level only. Cardiomyocyte cell culture systems exist, but cells lack physiologically essential structures such as organized sarcomeres and t-tubules required for myocyte function within the heart. In the protocol presented here, cardiomyocytes are isolated via Langendorff perfusion. The heart is removed from the mouse, mounted via the aorta to a cannula, perfused with digestion enzymes, and cells are introduced to increasing calcium concentrations. Edge and sarcomere detection software is used to analyze contractility, and a calcium binding fluorescent dye is used to visualize calcium transients of electrically paced cardiomyocytes; increasing understanding of the role cellular changes play in heart dysfunction. Traditionally used to test drug effects on cardiomyocytes, we employ this system to compare myocytes from WT mice and mice with a mutation that causes dilated cardiomyopathy. This protocol is unique in its comparison of live cells from mice with known heart function and known genetics. Many experimental conditions are reliably compared, including genetic or environmental manipulation, infection, drug treatment, and more. Beyond physiologic data, isolated cardiomyocytes are easily fixed and stained for cytoskeletal elements. Isolating cardiomyocytes via perfusion is an extremely versatile method, useful in studying cellular changes that accompany or lead to heart failure in a variety of experimental conditions.

Individual cardiomyocytes from wild type and mutant mice can be isolated from the heart in order to study their contractility and calcium transients. This allows characterization of the contribution of cellular dysfunction to heart dysfunction from any cause.

Cardiomyocytes, the workhorse cell of the heart, contain exquisitely organized cytoskeletal and contractile elements that generate the contractile force ...

Isolation of Small Noncoding RNAs from Human Serum

The analysis of RNA and its expression is a common feature in many laboratories. Of significance is the emergence of small RNAs like microRNAs, which are found in mammalian cells. These small RNAs are potent gene regulators controlling vital pathways such as growth, development and death and much interest has been directed at their expression in bodily fluids. This is due to their dysregulation in human diseases such as cancer and their potential application as serum biomarkers. However, the analysis of miRNA expression in serum may be problematic. In most cases the amount of serum is limiting and serum contains low amounts of total RNA, of which small RNAs only constitute 0.4-0.5%1. Thus the isolation of sufficient amounts of quality RNA from serum is a major challenge to researchers today. In this technical paper, we demonstrate a method which uses only 400 &#181;l of human serum to obtain sufficient RNA for either DNA arrays or qPCR analysis. The advantages of this method are its simplicity and ability to yield high quality RNA. It requires no specialized columns for purification of small RNAs and utilizes general reagents and hardware found in common laboratories. Our method utilizes a Phase Lock Gel to eliminate phenol contamination while at the same time yielding high quality RNA. We also introduce an additional step to further remove all contaminants during the isolation step. This protocol is very effective in isolating yields of total RNA of up to 100 ng/&#181;l from serum but can also be adapted for other biological tissues.

This protocol describes a method for extracting small RNAs from human serum. We have used this method to isolate microRNAs from cancer serum for use in DNA arrays and also singleplex quantitative PCR. The protocol utilizes phenol and guanidinium thiocyanate reagents with modifications to yield high quality RNA.

The analysis of RNA and its expression is a common feature in many laboratories. Of significance is the emergence of small RNAs like microRNAs, which are ...

Isolation of Myofibroblasts from Mouse and Human Esophagus

Murine and human esophageal myofibroblasts are generated via enzymatic digestion. Neonate (8-12 day old) murine esophagus is harvested, minced, washed, and subjected to enzymatic digestion with collagenase and dispase for 25 min. Human esophageal resection specimens are stripped of muscularis propria and adventitia and the remaining mucosa is minced, and subjected to enzymatic digestion with collagenase and dispase for up to 6 hr. Cultured cells express &#945;-SMA and vimentin and express desmin weakly or not at all. Culture conditions are not conducive to growth of epithelial, hematopoietic, or endothelial cells. Culture purity is further confirmed by flow cytometric evaluation of cell surface marker expression of potential contaminating hematopoietic and endothelial cells. The described technique is straightforward and results in consistent generation of non-hematopoieitc, non-endothelial stromal cells. Limitations of this technique are inherent to the use of primary cultures in molecular biology studies, i.e., the unavoidable variability encountered among cultures established across different mice or humans. Primary cultures however are a more representative reflection of the in vivo state compared to cell lines. These methods also provide investigators the ability to isolate and culture stromal cells from different clinical and experimental conditions, allowing comparisons between groups. Characterized esophageal stromal cells can also be used in functional studies investigating epithelial-stromal interactions in esophageal disorders.

We present a protocol to generate primary cultures of murine and human esophageal stromal cells with a myofibroblast phenotype. Cultured cells have spindle shaped morphology, express &#945;-SMA and vimentin, and lack epithelial, hematopoietic and endothelial cell surface markers. Characterized stromal cells can be used in functional studies of epithelial-stromal interactions.

Murine and human esophageal myofibroblasts are generated via enzymatic digestion. Neonate (8-12 day old) murine esophagus is harvested, minced, washed, ...

Isolation, Culture and Transduction of Adult Mouse Cardiomyocytes

Cultured cardiomyocytes can be used to study cardiomyocyte biology using techniques that are complementary to in vivo systems. For example, the purity and accessibility of in vitro culture enables fine control over biochemical analyses, live imaging, and electrophysiology. Long-term culture of cardiomyocytes offers access to additional experimental approaches that cannot be completed in short term cultures. For example, the in vitro investigation of dedifferentiation, cell cycle re-entry, and cell division has thus far largely been restricted to rat cardiomyocytes, which appear to be more robust in long-term culture. However, the availability of a rich toolset of transgenic mouse lines and well-developed disease models make mouse systems attractive for cardiac research. Although several reports exist of adult mouse cardiomyocyte isolation, few studies demonstrate their long-term culture. Presented here, is a step-by-step method for the isolation and long-term culture of adult mouse cardiomyocytes. First, retrograde Langendorff perfusion is used to efficiently digest the heart with proteases, followed by gravity sedimentation purification. After a period of dedifferentiation following isolation, the cells gradually attach to the culture and can be cultured for weeks. Adenovirus cell lysate is used to efficiently transduce the isolated cardiomyocytes. These methods provide a simple, yet powerful model system to study cardiac biology.

This protocol describes a step-by-step method for the reproducible isolation and long-term culture of adult mouse cardiomyocytes with high yield, purity, and viability.

Cultured cardiomyocytes can be used to study cardiomyocyte biology using techniques that are complementary to in vivo systems. For example, the purity and ...