Abstract
Modern concepts for the treatment of myocardial diseases focus on novel cell therapeutic strategies involving stem cell-derived cardiomyocytes (SCMs). However, functional integration of SCMs requires similar electrophysiological properties as primary cardiomyocytes (PCMs) and the ability to establish intercellular connections with host myocytes in order to contribute to the electrical and mechanical activity of the heart. The aim of this project was to investigate the properties of cardiac conduction in a co-culture approach using SCMs and PCMs in cultured cell strands. Murine embryonic SCMs were pooled with fetal ventricular cells and seeded in predefined proportions on microelectrode arrays to form patterned strands of mixed cells. Conduction velocity (CV) was measured during steady state pacing. SCM excitability was estimated from action potentials measured in single cells using the patch clamp technique. Experiments were complemented with computer simulations of conduction using a detailed model of cellular architecture in mixed cell strands. CV was significantly lower in strands composed purely of SCMs (5.5 ± 1.5 cm/s, n = 11) as compared to PCMs (34.9 ± 2.9 cm/s, n = 21) at similar refractoriness (100% SCMs: 122 ± 25 ms, n = 9; 100% PCMs: 139 ± 67 ms, n = 14). In mixed strands combining both cell types, CV was higher than in pure SCMs strands, but always lower than in 100% PCM strands. Computer simulations demonstrated that both intercellular coupling and electrical excitability limit CV. These data provide evidence that in cultures of murine ventricular cardiomyocytes, SCMs cannot restore CV to control levels resulting in slow conduction, which may lead to reentry circuits and arrhythmias.
Highlights
Stem cell-based therapy represents the new hope for cardiac repair of the injured heart after damage or disease
We have recently shown that stem cell-derived cardiomyocytes (SCMs) exhibit significantly lower levels of connexin 43 (Cx43) both at mRNA and protein levels compared with native primary myocytes, resulting in strongly reduced intercellular coupling of cell pairs (Marcu et al, 2015)
The SCM Proportion in Cultured Strands Matches that Determined at the Time of Seeding Since primary cardiomyocytes (PCMs) and GFP-tagged SCMs may exhibit different viabilities and attach with different strengths on the culture substrate, we first evaluated whether the proportion of PCMs and SCMs corresponded to the proportion that was predefined at the time of seeding
Summary
Stem cell-based therapy represents the new hope for cardiac repair of the injured heart after damage or disease. Major advances have been achieved in this field and provide strong evidence for the high potential of grafted cells to survive and functionally replace diseased cardiomyocytes (Shiba et al, 2012; Chong et al, 2014). Insufficient excitability or defective intercellular coupling may significantly alter electrical conduction and contribute to the development of arrhythmias (Yao et al, 2003; Danik et al, 2004; Liao et al, 2010). Impulse propagation across the myocardium is determined by various parameters that control myocyte excitability, action potential (AP) properties and intercellular resistance (Kléber and Rudy, 2004; Veeraraghavan et al, 2014). The electrical excitability of a cardiomyocyte depends on the sarcolemmal ion channel repertoire and functional expression of fast voltage-dependent Na+ channels, which define the upstroke of the AP (Weidmann, 1955; Berecki et al, 2010). Reduced Na+ current (INa) may significantly alter the AP upstroke and reduce myocyte excitability
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