Blebbistatin is a recently discovered myosin II inhibitor. It is rapidly becoming a compound of choice to reduce motion artifacts during cardiac optical mapping, as well as to study cell motility and cell invasion. Although blebbistatin has a number of advantages over other electromechanical uncouplers, many of its properties have yet to be addressed. Here we describe several methodological issues associated with the use of blebbistatin, including its spectral properties, reversibility, and its effect on tissue metabolic state. We show that if precautions are not taken, perfusion with blebbistatin may result in blebbistatin precipitate that accumulates in the vasculature. Although such precipitate is fluorescent, it is not detectable within wavelength bands that are typically used for transmembrane voltage fluorescence imaging (i.e., emission wavelengths >600 nm). Therefore, blockage of the microcirculation by blebbistatin may cause data misinterpretation in studies that use voltage-sensitive dyes. Blebbistatin may also impact imaging of green fluorophores due to the spectral shift it causes in endogenous tissue fluorescence. 3D excitation–emission matrices of blebbistatin in precipitate form and in various solutions (DMSO, water, and 1 % aqueous albumin) revealed significant changes in the fluorescence of this molecule in different environments. Finally, we examined the reversibility of blebbistatin’s uncoupling effect on cardiac contraction. Our findings provide important new information about the properties of this myosin II inhibitor, which will aid in the proper design and interpretation of studies that use this compound.

This study characterizes a powerful and clinically relevant new model for studies of cardiac arrhythmias generated by increasing the activity of sympathetic nerve terminals and the resulting activation of myocyte β-adrenergic receptors.

Background: Phthalates are common plasticizers present in medical-grade plastics and other everyday products. They can also act as endocrine-disrupting chemicals and have been linked to the rise in metabolic disorders. However, the effect of phthalates on cardiac metabolism remains largely unknown.Objectives: We examined the effect of di(2-ethylhexyl)phthalate (DEHP) on the metabolic profile of cardiomyocytes because alterations in metabolic processes can lead to cell dysfunction.Methods: Neonatal rat cardiomyocytes were treated with DEHP at a concentration and duration comparable to clinical exposure (50–100 μg/mL, 72 hr). We assessed the effect of DEHP on gene expression using microarray analysis. Physiological responses were examined via fatty acid utilization, oxygen consumption, mitochondrial mass, and Western blot analysis.Results: Exposure to DEHP led to up-regulation of genes associated with fatty acid transport, esterification, mitochondrial import, and β-oxidation. The functional outcome was an increase in myocyte fatty acid–substrate utilization, oxygen consumption, mitochondrial mass, PPARα (peroxisome proliferator-activated receptor α) protein expression, and extracellular acidosis. Treatment with a PPARα agonist (Wy-14643) only partially mimicked the effects observed in DEHP-treated cells.Conclusions: Data suggest that DEHP exposure results in metabolic remodeling of cardiomyocytes, whereby cardiac cells increase their dependence on fatty acids for energy production. This fuel switch may be regulated at both the gene expression and posttranscription levels. Our findings have important clinical implications because chronic dependence on fatty acids is associated with an accumulation in lipid intermediates, lactate, protons, and reactive oxygen species. This dependence can sensitize the heart to ischemic injury and ventricular dysfunction.

Background: Bisphenol A (BPA) is used to produce polycarbonate plastics and epoxy resins that are widely used in everyday products, such as food and beverage containers, toys, and medical devices. Human biomonitoring studies have suggested that a large proportion of the population may be exposed to BPA. Recent epidemiological studies have reported correlations between increased urinary BPA concentrations and cardiovascular disease, yet the direct effects of BPA on the heart are unknown.Objectives: The goal of our study was to measure the effect of BPA (0.1–100 μM) on cardiac impulse propagation ex vivo using excised whole hearts from adult female rats.Methods: We measured atrial and ventricular activation times during sinus and paced rhythms using epicardial electrodes and optical mapping of transmembrane potential in excised rat hearts exposed to BPA via perfusate media. Atrioventricular activation intervals and epicardial conduction velocities were computed using recorded activation times.Results: Cardiac BPA exposure resulted in prolonged PR segment and decreased epicardial conduction velocity (0.1–100 μM BPA), prolonged action potential duration (1–100 μM BPA), and delayed atrioventricular conduction (10–100 μM BPA). These effects were observed after acute exposure (≤ 15 min), underscoring the potential detrimental effects of continuous BPA exposure. The highest BPA concentration used (100 μM) resulted in prolonged QRS intervals and dropped ventricular beats, and eventually resulted in complete heart block.Conclusions: Our results show that acute BPA exposure slowed electrical conduction in excised hearts from female rats. These findings emphasize the importance of examining BPA’s effect on heart electrophysiology and determining whether chronic in vivo exposure can cause or exacerbate conduction abnormalities in patients with preexisting heart conditions and in other high-risk populations.Citation: Posnack NG, Jaimes R III, Asfour H, Swift LM, Wengrowski AM, Sarvazyan N, Kay MW. 2014. Bisphenol A exposure and cardiac electrical conduction in excised rat hearts. Environ Health Perspect 122:384–390; http://dx.doi.org/10.1289/ehp.1206157