Abstract
Ca2+ activated non-selective (CAN) cation channels have been described in cardiomyocytes since the advent of the patch clamp technique. It has been hypothesized that this type of ion channel contributes to the triggering of cardiac arrhythmias. TRPM4 is to date the only molecular candidate for a CAN cation channel in cardiomyocytes. Its significance for arrhythmogenesis in living animals remains, however, unclear. In this study, we have tested whether increased expression of wild-type (WT) TRPM4 augments the risk of arrhythmias in living mice. Overexpression of WT TRPM4 was achieved via tail vein injection of adeno-associated viral vector serotype 9 (AAV9) particles, which have been described to be relatively cardiac specific in mice. Subsequently, we performed ECG-measurements in freely moving mice to determine their in vivo cardiac phenotype. Though cardiac muscle was transduced with TRPM4 viral particles, the majority of viral particles accumulated in the liver. We did not observe any difference in arrhythmic incidents during baseline conditions. Instead, WT mice that overexpress TRPM4 were more vulnerable to develop premature ventricular ectopic beats during exercise-induced β-adrenergic stress. Conduction abnormalities were rare and not more frequent in transduced mice compare to WT mice. Taken together, we provide evidence that overexpression of TRPM4 increases the susceptibility of living mice to stress-induced arrhythmias.
Highlights
The Transient Receptor Potential Melastatin member 4 (TRPM4) is a Ca2+ activated nonselective (CAN) cation channel (Launay et al, 2002; Nilius et al, 2003)
Woodchuck Hepatitis Virus Posttranscriptional Regulatory Element (WPRE) was retained giving a total size of 5645 bp (Figure 1A), while in the other transfer construct, the WPRE was removed resulting in a smaller size of 5093 bp (Figure 1B)
Both plasmid constructs were transfected into HEK293T cells to verify protein expression and were confirmed to produce functional TRPM4 channels by patch clamp
Summary
The Transient Receptor Potential Melastatin member 4 (TRPM4) is a Ca2+ activated nonselective (CAN) cation channel (Launay et al, 2002; Nilius et al, 2003). The role of CAN channels in the heart muscle is somewhat illustrious Considering that these channels are active when the intracellular Ca2+ concentration is increased, they might contribute to action potential (AP) duration and Na+ influx during the AP. We and others have previously shown that TRPM4 is expressed and functionally active in cardiomyocytes (Demion et al, 2007; Abriel et al, 2012; Kruse and Pongs, 2014; Mathar et al, 2014). Following up on the concept of Kruse et al (2009), we tested whether overexpression of TRPM4 per se predisposes living mice to heart rhythm abnormalities. To this end, we used tail-vein injection of adeno-associated viral vector serotype 9 (AAV9) particles encoding TRMP4. Among all available AAV-serotypes, AAV9 has the best cardiotropic properties (Wright et al, 2001; Vandendriessche et al, 2007; Zincarelli et al, 2008)
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