ARTICLE Cardiac Myocytes’ Dynamic Contractile Behavior Differs Depending on Heart Segment Emerson J. De Souza, 1 Wylie Ahmed, 1 Vincent Chan, 2 Rashid Bashir, 2 Taher Saif 1 1 Department of Mechanical Science and Engineering, University of Illinois at Urbana Champaign, Illinois, 142 MEB MC: 244, 1206 W. Green Street, Urbana, Illinois 61801; telephone: 217-333-0958; fax: 217-244-9980; e-mail: emerson.jose.desouza@gmail.com 2 Department of Micro and Nanotechnology, University of Illinois at Urbana Champaign, Illinois, Urbana, Illinois ABSTRACT: Cardiac myocytes originating from different parts of the heart exhibit varying morphology and ultra- structure. However, the difference in their dynamic behavior is unclear. We examined the contraction of cardiac myocytes originating from the apex, ventricle, and atrium, and found that their dynamic behavior, such as amplitude and frequen- cy of contraction, differs depending on the heart segment of origin. Using video microscopy and high-precision image correlation, we found that: (1) apex myocytes exhibited the highest contraction rate (17 beats/min); (2) ventricular myocytes exhibited the highest contraction amplitude (5.2 micron); and (3) as myocyte contraction synchro- nized, their frequency did not change significantly, but the amplitude of contraction increased in apex and ventricular myocytes. In addition, as myocyte cultures mature they formed contractile filaments, further emphasizing the dif- ference in myocyte dynamics is persistent. These results suggest that the dynamic behavior (in addition to static properties) of myocytes is dependent on their segment of origin. Biotechnol. Bioeng. 2013;110: 628–636. ß 2012 Wiley Periodicals, Inc. KEYWORDS: cardiac tissue engineering; cell transplanta- tion; heart physiology; sarcomere length; myocyte filament Introduction The heart consists of many types of cells and their properties vary depending on their spatial location (e.g., pacemaker, conducting tissues, atrial and ventricular walls, etc.) (Barnett, 2005a; Laske and Iaizzo, 2005; Opie, 2004). It is well known that morphology and structure of cells in the heart differ and this has driven studies of heart shape and size for over a century (Burton, 1957; Kyrieleis, 1963; Thomson, 1896). For instance, the duration of action potentials is different in atrium, ventricle, and Purkinje fibers with values of 150, 250, and 300 ms, respectively (Barnett, 2005b; Laske and Iaizzo, 2005). Right and left apex has been distinguished by increase of its surface area and relative cell alignment during heart looping (Manasek et al., 1972). Electromechanical coupling demonstrated that increased contraction force following an increase in stimulation frequency was significantly higher in atrium than in ventricle (Schwinger, 1993). Pacing at the right ventricular apex adversely affects hemodynamics, while pacing at the left ventricular septum or apex causes best function because pacing from these sites creates a physiological propagation of electrical conduction (Peschar, 2003). Atrial and ventricle myocardium have shown different mechanism of force generation in response to external stretching (Kockska ¨mper et al., 2008). The examples above display the relationship between regions of the heart and heart function at the full organ level (1936; Barnett, 2005b; Burton, 1957; Kockska ¨mper et al., 2008; Kyrieleis, 1963; Manasek et al., 1972; Peschar, 2003; Schwinger, 1993; Thomson, 1896), while studies in the 1950s and 1960s revealed the importance of understanding the individual myocyte behavior for the full organ function (Burton, 1957; Kyrieleis, 1963). The relationship between individual myocytes and the full organ became the motivation to continue investigating different segments of heart tissues (Kockska ¨mper et al., 2008; Legato, 1970; Schwinger, 1993; Sommer and Johnson, 1968), to distin- guish individual myocytes (Manasek et al., 1972; Silver et al., 1983), and to measure the force at the cellular level (Jacot et al., 2010; Linder et al., 2010). In the context of individual myocytes in vitro, the contraction rate and amplitude of myocardial cells became fundamental observables, because they allow the extraction of mechanical and biochemical information between myocytes and their microenviron- ment. Engler et al. (2008) has shown, for example, that Correspondence to: E. J. De Souza Contract grant sponsor: U.S. Army Medical Research & Material Command (USAMRMC) Contract grant sponsor: The Telemedicine & Advanced Technology Research Center (TATRC) Contract grant number: W81XWH0810701 Received 5 March 2012; Revision received 28 August 2012; Accepted 30 August 2012 Accepted manuscript online 5 September 2012; Article first published online 23 October 2012 in Wiley Online Library (http://onlinelibrary.wiley.com/doi/10.1002/bit.24725/abstract) DOI 10.1002/bit.24725 628 Biotechnology and Bioengineering, Vol. 110, No. 2, February, 2013 ß 2012 Wiley Periodicals, Inc.