Abstract 2427: Arrhythmogenic Effects of Transforming Growth Factor-β1 on Hybrid Cardiomyocyte-Myofibroblast Preparations
Introduction: Structural remodeling of the heart is typically accompanied by the appearance of myofibroblasts (MFBs) in the working myocardium. In-vitro, MFBs were shown to induce arrhythmogenic slow conduction and ectopic activity by virtue of acting as a source of depolarizing current for cardiomyocytes following establishment of heterocellular gap junctional coupling. Because differentiation and proliferation of MFBs is primarily controlled by transforming growth factor-β1 (TGF-β1), we investigated whether TGF-β1 might additionally affect MFB arrhythmogenicity.
Methods: Experiments were performed with primary co-cultures of neonatal rat ventricular cardiomyocytes and cardiac MFBs. Conduction velocities (𝛉) in patterned growth strand preparations were assessed optically whereas resting membrane potentials (RMPs) in single cells and hybrid cell pairs were recorded using standard patch clamp techniques. Data are given as mean±S.D. (n=5 to 41).
Results: TGF-β1 applied to pure cardiomyocyte preparations at 2.5 ng/ml for 24 – 48 hrs had minimal effects on RMPs (−77±2 mV vs. −76±2 mV) and 𝛉 (385±39 mm/s vs. 337±50 mm/s). In contrast, TGF-β1 caused a substantial depolarization of single MFBs from −29±6 mV to −20±6 mV. Similarly, TGF-β1 significantly depolarized cardiomyocyte-MFB cell pairs from −61±10 mV to −53±11 mV and reduced α in MFB coated cardiomyocyte strands in a dose dependent manner from 305±38 mm/s to 124±45 mm/s (2.5 ng/ml for 24 hrs; EC50 ~ 0.15 ng/ml). On the other hand, blockade of TGF-β1 receptors with SB-431542 (10 μmol/L; 24 to 48 hrs) in the absence of exogenously added TGF-β1 significantly hyperpolarized single MFBs from −29±6 mV to −55.1±18.1 mV and cardiomyocyte-MFB cell pairs from −61±10 mV to −68.5±8.8 mV. At the multicellular level, exposure of MFB coated cardiomyocyte strands to SB-431542 resulted in an increase of 𝛉 from 305±38 mm/s to 367±32 mm/s, i.e., to levels of pure cardiomyocyte strands.
Conclusions: These results demonstrate that both exogenous and endogenously produced TGF-β1 is of central importance for the ability of MFBs to exert arrhythmogenic effects on cardiomyocytes. In this context, the results might form a mechanistic basis for the recent proposition to use TGF-β1 as a risk stratifier for cardiac arrhythmias.