鼠心肌细胞的分离及生理分析
Summary
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.
Abstract
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.
Introduction
Cardiomyocytes provide the contractile force for the heart. Each myocyte contains organized cytoskeletal and contractile elements essential to contraction. The heart not only contains cardiomyocytes but also fibroblasts, connective tissue, and modified myocytes such as Purkinje fibers. Changes in any or all of these cell types can be seen in heart failure, making determination of the ultimate cause of heart dysfunction difficult. Decreased ventricular contractility of a failing heart is preceded by varying degrees of fibrous tissue build-up and hypertrophy and dysfunction of the cardiomyocytes1. Arrhythmias can be caused by dysfunction in the conducting cells2, fibrosis interrupting cardiac conduction3, or changes in the expression of ion channels in cardiomyocytes1,4. Indeed, these problems often co-exist in a complicated fashion.
Isolating and studying cardiomyocytes allows one to examine contractile and electrical dysfunction of individual myocytes in the context of overall heart function. Techniques to isolate individual cardiac myocytes were developed over 40 years ago in an effort to better study physiology of this ‘workhorse’ cell of the heart. Isolation techniques have been improved to increase yield and quality of cells, with the vital development of coronary perfusion via cannulation of the aorta, first performed in 19705. This article describes cardiomyocyte isolation followed by measurement of contractility and calcium transients using ratiometric fluorescence and cell dimensioning data acquisition software. In both genetic and environmental models of heart disease, utilizing this protocol provides key information about cell contractility, sarcomeric contractility and relaxation, calcium transients, and cytoskeletal disruption. This system is often used to test the effect of drugs on isolated cardiomyocytes6,7. We employ the system to compare contractility and calcium transients of cardiomyocytes between wild type mice and mice with a mutation leading to dilated cardiomyopathy.
Studying individual cardiac myocytes has numerous advantages over other commonly used methods to study cardiac anatomy and physiology. Echocardiography and electrocardiography provide information about the contractile function and electrical conduction of the heart overall. Neither of these methods explains the cause or nature of the dysfunction below the level of the whole organ. Measuring contractility of individual cardiomyocytes using edge-detection and sarcomere length algorithms can demonstrate that changes within the contractile cell of the heart are present within global heart dysfunction. Measuring calcium transients demonstrates the influence of changes in ion flux at a cellular level to contractile dysfunction or arrhythmias.
In addition to complementing whole organ studies, this protocol provides cells easily stained for sub-cellular components. It is possible to see cytoskeletal changes by staining tissue sections of the whole heart; however, one is only able to visualize a cross section of cells. A whole cardiomyocyte is thicker than the typical tissue section, and given the arrangement and length of the cardiomyocytes, it is difficult to see whole cells in a single section. Isolated cardiomyocytes can be fixed immediately and stained for a variety of cytoskeletal elements and ion channels. Confocal images can be compiled into full thickness z-stacks of the cell. Additionally, staining isolated cardiac myocytes allows for staining of components that are impossible to visualize in sections, such as the membrane invaginations known as t-tubules.
Cultured cell lines of cardiac myocytes do exist, some of which have similar transcriptional profiles and phenotypic features to cardiac myocytes. Some, such as the HL-1 cell line, even retain some sarcomeric organization and rudimentary contractile ability8. Despite these qualities, cultured cells lack the “box car” shape and t-tubule structure of cardiomyocytes and have less sarcomeric organization. These components are essential to the function of cardiomyocytes in vivo. In addition, using cultured cells allows genetic manipulation but not in vivo physiologic manipulation. Isolated cardiomyocytes retain their cellular organization long enough to study but are still easily imaged and even transduced9.
Isolated cardiomyocytes are extremely versatile, providing a substrate to identically analyze cells from varied experimental conditions. Isolation and physiological analysis of myocytes have been used by countless labs for a variety of experiments including studying the effect of drugs6,7 or small molecules10, environmental stressors11, infection12, illness13, or genetic mutation14,15 on contractility and/or calcium transients and studying the regulation of contractility and calcium release within a cardiomyocyte15-17. With the application of any of these stressors, changes in heart function could be due to any combination of changes in the cardiomyocytes themselves and changes in the surrounding environment of the heart, such as scarring, changes in conductivity, or changes to the extracellular matrix. This is an ideal protocol for answering research questions regarding individual myocyte structure and function in the context of heart failure from any cause.
Although it has countless advantages over other techniques, physiological analysis of isolated cardiomyocytes is not ideal for every research question. Isolation is a terminal procedure, thus cardiomyocytes can only be assessed at one time in the mouse’s life. This can be partially overcome using cohorts and sacrificing individual mice along the course of illness development or by monitoring the mouse to determine whether it has clinically significant heart failure before isolation. Although this protocol can determine whether cardiomyocyte dysfunction has occurred, one cannot draw the conclusion that this dysfunction is the root cause of heart failure without additional experimental information. It is possible that cardiomyocyte dysfunction itself is secondary to other changes in the heart. Despite these challenges, studying cardiomyocytes offers valuable information in determining the nature of dysfunction in the heart, especially when combined with other experiments.
The following protocol is adapted from one provided by Dr. Chee Lim, Vanderbilt University. Although contractility and calcium flux data are highly reproducible and useful in comparing hearts with genetic or environmental manipulation, isolation itself remains a technique dependent protocol, requiring optimization. Minimizing the time between removing the heart from the mouse and perfusing the heart via aortic cannulation is essential for a quality digestion. In addition, digestion time and enzyme concentration can be optimized for the highest quality myocytes. Steps likely requiring optimization, along with suggestions for optimization, are noted below.
Protocol
Representative Results
Discussion
的质量的心肌细胞的分离需要实践和优化的一些水平。该协议包含可大大影响消化的结果的关键步骤。执行和解决方案时，这些应慎重考虑。从拆除的心脏插管灌注的时间应尽量减少，最好不超过五分钟。从鼠标在冰冷的缓冲液去除，并解剖和cannulating的心脏后，在冰冷的缓冲液灌注冲洗，立即的心脏也将增加优质消化的机会。插管本身是关键的一步。插管的尖端必须放在下面主动脉的第一分支?…
Divulgazioni
The authors have nothing to disclose.
Acknowledgements
马克·沃兹尼亚克在细胞与发育生物学录像设备的使用部门。
范德堡大学细胞成像共享资源。
这项工作是由美国心脏协会授予12PRE10950005到ERP系统，美国心脏协会授予11GRNT7690040到DMB，美国国立卫生研究院资助R01 HL037675到DMB的支持。 DMB是格拉迪斯体育斯塔尔曼主席在心血管研究。
Materials
| NaCl | RPI | S23020 | |
| KCl | Sigma | P-3911 | |
| MgCl2 | Sigma | M-8266 | |
| HEPES | EM Science | S320 | |
| NaH2PO4 | Sigma | S5011 | |
| CaCl2 Ÿ 2H2O | Fisher | C79 | |
| D-(+)-Glucose | Sigma | G7528 | |
| 2,3-Butanedione-monoxime (BDM) | Sigma | B-0753 | |
| Taurine | Sigma | T-0625 | |
| Bovine Serum Albumin (BSA) | Sigma | A-7030 | |
| Collagenase B | Roche Diagnostics | 1-088-823 | |
| Collagenase D | Roche Diagnostics | 1-088-882 | |
| Protease XIV | Sigma | P-5147 | |
| Heparin | APP Pharmaceuticals, LLC | 401586D | |
| Isofluorane | Butler Schein | 11695-6776-2 | |
| Fura-2 AM | Teflabs | 103 | |
| DMSO – anhydrous | Sigma | 276855 | |
| IonOptix cell pacing and fluorescent analysis system | IonOptix | ||
| 250 um nylon mesh filter | Sefar America | Lab Pak 03-250/50 | |
| 23G leur-stub adaptor | Becton Dickinson | 1482619E | |
| PE-50 tubing | Becton Dickinson | 427410 |
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