This work was supported by funding from American Heart Association 12BGIA12040477, NC State University Chancellor&#8217;s Faculty Excellence Program, and National Natural Science Foundation of China H020381370216.

The following protocol is designed for the isolation of cardiomyocytes from one litter of neonatal rat pups (10-14 pups). If litter size is significantly different, the procedure may have to be scaled to compensate. The pups should be around 48&#177;6 hr old. All procedures herein have been approved by the North Carolina State University Institutional Animal Care and Usage Committee (IACUC).
1. Cell Isolation Preparation
NOTE: Perform the following steps the day befor...

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The authors have nothing to disclose.

This protocol allows for the NRCMs to be isolated, cryopreserved, and thawed. Thawing the cells is a crucial portion of the procedure. A series of DMSO dilutions is used to slowly remove DMSO from the cells14. It is important that the extraction of DMSO be performed quickly as the cells are particularly sensitive to dying immediately after thawing. If more or less cells are required for thawing, the volumes of the DMSO solutions can be scaled as needed.
One challenge to NRCM isolati...

Cell culture of cardiomyocytes is a critical tool in modern cardiac research. Neonatal rat cardiomyocytes (NRCMs) are commonly used since the isolation and culture is easier than that of adult rat cardiomyocytes1. The NRCM method still has several limitations including a long isolation procedure and limited cell proliferation in the dish. There are numerous protocols for the isolation of NRCMs with most generally requiring 4-48 hr of work2&#8211;6. In addition, the cells are frequently isolated from 1 to 2-day old rat pups2,4&#8211;7; the timing of the birth can be unpredictable and conflict with other work in the lab. The isolations can be inefficient and wasteful if only a small amount of cells are needed for experiments. Most efforts on improving the workflow focus on reducing the isolation time, yet this does not solve the problems of timing the birth of the pups.
As alternatives, many labs utilize cardiomyocytes derived from embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs). However, the reprogramming and/or differentiation process can be very time consuming and costly as well. There can be other problems when using these cells as in vitro myocyte models. Both ESC- and iPSC- derived cardiomyocytes have been shown to exhibit differences in electrophysiology from primary cardiomyocytes8&#8211;10.
Dissociated NRCMs are capable of being stored for several days using refrigeration11, yet this does allow for long term storage. Liquid nitrogen is typically used to preserve cells for a greater period of time, but requires a cryoprotectant such as dimethyl sulfoxide (DMSO). Previous research has shown that the ideal concentration between 5-10% DMSO in the freezing media allows for cryopreservation of NRCMs, yet even then the viability remains low12. Although DMSO helps protect the cells during freezing, it can be toxic to cells at concentrations above 1.5%13. Previous studies have shown that slowly removing DMSO from the cells, may improve cell viability14.
We sought to improve the efficiency of NRCM cell-based assays by cryopreserving the cells following isolation. This allows for the cells to be thawed and used when necessary, reducing the frequency of isolations and consumption of animals. Using this method, we show that it is possible to cryopreserve NRCMs and thaw them for use at a later time. After thawing the cells maintain an acceptable viability and produce NRCM cultures that are positive for &#945;-sarcomeric actinin (&#945;-SA) and contract spontaneously.

<table border="0" cellpadding="0" cellspacing="0">
	<tbody>
		<tr>
			<td>IMDM (+25mM HEPES +L-glutamine)</td>
			<td>Gibco</td>
			<td>12440-046</td>
			<td>With added 25mM HEPES and L-glutamine</td>
		</tr>
		<tr>
			<td>L-glutamine</td>
			<td>Gibco</td>
			<td>25030-081</td>
			<td></td>
		</tr>
		<tr>
			<td>FBS</td>
			<td>Hyclone</td>
			<td>SH30070.03</td>
			<td></td>
		</tr>
		<tr>
			<td>Gentamicin</td>
			<td>Gibco</td>
			<td>15710-064</td>
			<td></td>
		</tr>
		<tr>
			<td>2-Mercaptoethanol</td>
			<td>Gibco</td>
			<td>21985-023</td>
			<td></td>
		</tr>
		<tr>
			<td>HBSS (+Ca +Mg)</td>
			<td>Corning</td>
			<td>21-020-CV</td>
			<td>With added calcium and magnesium, pH 7.1-7.4</td>
		</tr>
		<tr>
			<td>Trypsin 0.25%</td>
			<td>Gibco</td>
			<td>25300-056</td>
			<td></td>
		</tr>
		<tr>
			<td>Trypsin 0.05%</td>
			<td>Gibco</td>
			<td>25300-054</td>
			<td></td>
		</tr>
		<tr>
			<td>Cryostor CS5</td>
			<td>BioLife Solutions</td>
			<td>205102</td>
			<td>Freezing media</td>
		</tr>
		<tr>
			<td>Cryogenic Vial</td>
			<td>Corning</td>
			<td>430659</td>
			<td></td>
		</tr>
		<tr>
			<td>Collagenase</td>
			<td>Sigma</td>
			<td>C1889-50MG</td>
			<td></td>
		</tr>
		<tr>
			<td>40&#956;m Cell Strainer</td>
			<td>Greiner Bio-One</td>
			<td>542040</td>
			<td></td>
		</tr>
		<tr>
			<td>Sterilizing Vacuum Filter (0.22&#956;m)</td>
			<td>Corning</td>
			<td>431118</td>
			<td></td>
		</tr>
		<tr>
			<td>50mL Conical</td>
			<td>Corning</td>
			<td>430828</td>
			<td></td>
		</tr>
		<tr>
			<td>15mL Conical</td>
			<td>Corning</td>
			<td>430790</td>
			<td></td>
		</tr>
		<tr>
			<td>trypan blue</td>
			<td>Cellgro</td>
			<td>25-900-CI</td>
			<td></td>
		</tr>
		<tr>
			<td>Mr Frosty Freezing Container</td>
			<td>ThermoScientific</td>
			<td>5100-0001</td>
			<td></td>
		</tr>
		<tr>
			<td>Millicell EZ&#160;SLIDES</td>
			<td>Millipore</td>
			<td>PEZGS0416</td>
			<td></td>
		</tr>
		<tr>
			<td>&#945;-sarcomeric actinin antibody</td>
			<td>Sigma</td>
			<td>A7811</td>
			<td></td>
		</tr>
		<tr>
			<td>Fibronectin</td>
			<td>Corning</td>
			<td>356008</td>
			<td></td>
		</tr>
		<tr>
			<td>Bromodeoxyuridine</td>
			<td>BD Biosciences</td>
			<td>51-7581KZ</td>
			<td></td>
		</tr>
	</tbody>
</table>

isolation and cryopreservation of neonatal rat cardiomyocytes

Cell culture has become increasingly important in cardiac research, but due to the limited proliferation of cardiomyocytes, culturing cardiomyocytes is difficult and time consuming. The most commonly used cells are neonatal rat cardiomyocytes (NRCMs), which require isolation every time cells are needed. The birth of the rats can be unpredictable. Cryopreservation is proposed to allow for cells to be stored until needed, yet freezing/thawing methods for primary cardiomyocytes are challenging due to the sensitivity of the cells. Using the proper cryoprotectant, dimethyl sulfoxide (DMSO), cryopreservation was achieved. By slowly extracting the DMSO while thawing the cells, cultures were obtained with viable NRCMs. NRCM phenotype was verified using immunocytochemistry staining for &#945;-sarcomeric actinin. In addition, cells also showed spontaneous contraction after several days in culture. Cell viability after thawing was acceptable at 40-60%. In spite of this, the methods outlined allow one to easily cryopreserve and thaw NRCMs. This gives researchers a greater amount of flexibility in planning experiments as well as reducing the use of animals.

Following the isolation of the neonatal rat cardiomyocytes, the cells are frozen down to liquid nitrogen, and can be stored for at least several months. Typically upon thawing, the viability determined by Trypan Blue analysis will be between 40-60%. Though this is lower than other cell types, with proper seeding and culture the cells will proliferate (Figure 1). In order to verify contractility, the cells can be imaged using a phase contrast microscopy. The cells should begin to spontaneously contract wi...

Watch this Scientific Journal Video about Isolation and Cryopreservation of Neonatal Rat Cardiomyocytes at JoVE.com

Isolation and Cryopreservation of Neonatal Rat Cardiomyocytes

The isolation of neonatal rat cardiomyocytes is a time consuming and unpredictable procedure. This study describes methods for cryopreservation and thawing of neonatal rat cardiomyocytes that allows for more efficient use of cells. The thawed NRCMs can be used for various experiments without the need for performing isolations each time.

Cell culture has become increasingly important in cardiac research, but due to the limited proliferation of cardiomyocytes, culturing cardiomyocytes is ...

isolation-and-cryopreservation-of-neonatal-rat-cardiomyocytes

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Developmental Biology

12.4K vistas.  College of Veterinary Medicine, North Carolina State University. The isolation of neonatal rat cardiomyocytes is a time consuming and unpredictable procedure. This study describes methods for cryopreservation and thawing of neonatal rat cardiomyocytes that allows for more efficient use of cells. The thawed NRCMs can be used for various experiments without the need for performing isolations each time.